libfc: Fix a race in fc_exch_timer_set_locked()

[deliverable/linux.git] / drivers / scsi / libfc / fc_exch.c

/*
 * Copyright(c) 2007 Intel Corporation. All rights reserved.
 * Copyright(c) 2008 Red Hat, Inc.  All rights reserved.
 * Copyright(c) 2008 Mike Christie
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Maintained at www.Open-FCoE.org
 */

/*
 * Fibre Channel exchange and sequence handling.
 */

#include <linux/timer.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/export.h>
#include <linux/log2.h>

#include <scsi/fc/fc_fc2.h>

#include <scsi/libfc.h>
#include <scsi/fc_encode.h>

#include "fc_libfc.h"

u16     fc_cpu_mask;            /* cpu mask for possible cpus */
EXPORT_SYMBOL(fc_cpu_mask);
static u16      fc_cpu_order;   /* 2's power to represent total possible cpus */
static struct kmem_cache *fc_em_cachep;        /* cache for exchanges */
static struct workqueue_struct *fc_exch_workqueue;

/*
 * Structure and function definitions for managing Fibre Channel Exchanges
 * and Sequences.
 *
 * The three primary structures used here are fc_exch_mgr, fc_exch, and fc_seq.
 *
 * fc_exch_mgr holds the exchange state for an N port
 *
 * fc_exch holds state for one exchange and links to its active sequence.
 *
 * fc_seq holds the state for an individual sequence.
 */

/**
 * struct fc_exch_pool - Per cpu exchange pool
 * @next_index:   Next possible free exchange index
 * @total_exches: Total allocated exchanges
 * @lock:         Exch pool lock
 * @ex_list:      List of exchanges
 *
 * This structure manages per cpu exchanges in array of exchange pointers.
 * This array is allocated followed by struct fc_exch_pool memory for
 * assigned range of exchanges to per cpu pool.
 */
struct fc_exch_pool {
        spinlock_t       lock;
        struct list_head ex_list;
        u16              next_index;
        u16              total_exches;

        /* two cache of free slot in exch array */
        u16              left;
        u16              right;
} ____cacheline_aligned_in_smp;

/**
 * struct fc_exch_mgr - The Exchange Manager (EM).
 * @class:          Default class for new sequences
 * @kref:           Reference counter
 * @min_xid:        Minimum exchange ID
 * @max_xid:        Maximum exchange ID
 * @ep_pool:        Reserved exchange pointers
 * @pool_max_index: Max exch array index in exch pool
 * @pool:           Per cpu exch pool
 * @stats:          Statistics structure
 *
 * This structure is the center for creating exchanges and sequences.
 * It manages the allocation of exchange IDs.
 */
struct fc_exch_mgr {
        struct fc_exch_pool __percpu *pool;
        mempool_t       *ep_pool;
        enum fc_class   class;
        struct kref     kref;
        u16             min_xid;
        u16             max_xid;
        u16             pool_max_index;

        struct {
                atomic_t no_free_exch;
                atomic_t no_free_exch_xid;
                atomic_t xid_not_found;
                atomic_t xid_busy;
                atomic_t seq_not_found;
                atomic_t non_bls_resp;
        } stats;
};

/**
 * struct fc_exch_mgr_anchor - primary structure for list of EMs
 * @ema_list: Exchange Manager Anchor list
 * @mp:       Exchange Manager associated with this anchor
 * @match:    Routine to determine if this anchor's EM should be used
 *
 * When walking the list of anchors the match routine will be called
 * for each anchor to determine if that EM should be used. The last
 * anchor in the list will always match to handle any exchanges not
 * handled by other EMs. The non-default EMs would be added to the
 * anchor list by HW that provides offloads.
 */
struct fc_exch_mgr_anchor {
        struct list_head ema_list;
        struct fc_exch_mgr *mp;
        bool (*match)(struct fc_frame *);
};

static void fc_exch_rrq(struct fc_exch *);
static void fc_seq_ls_acc(struct fc_frame *);
static void fc_seq_ls_rjt(struct fc_frame *, enum fc_els_rjt_reason,
                          enum fc_els_rjt_explan);
static void fc_exch_els_rec(struct fc_frame *);
static void fc_exch_els_rrq(struct fc_frame *);

/*
 * Internal implementation notes.
 *
 * The exchange manager is one by default in libfc but LLD may choose
 * to have one per CPU. The sequence manager is one per exchange manager
 * and currently never separated.
 *
 * Section 9.8 in FC-FS-2 specifies:  "The SEQ_ID is a one-byte field
 * assigned by the Sequence Initiator that shall be unique for a specific
 * D_ID and S_ID pair while the Sequence is open."   Note that it isn't
 * qualified by exchange ID, which one might think it would be.
 * In practice this limits the number of open sequences and exchanges to 256
 * per session.  For most targets we could treat this limit as per exchange.
 *
 * The exchange and its sequence are freed when the last sequence is received.
 * It's possible for the remote port to leave an exchange open without
 * sending any sequences.
 *
 * Notes on reference counts:
 *
 * Exchanges are reference counted and exchange gets freed when the reference
 * count becomes zero.
 *
 * Timeouts:
 * Sequences are timed out for E_D_TOV and R_A_TOV.
 *
 * Sequence event handling:
 *
 * The following events may occur on initiator sequences:
 *
 *      Send.
 *          For now, the whole thing is sent.
 *      Receive ACK
 *          This applies only to class F.
 *          The sequence is marked complete.
 *      ULP completion.
 *          The upper layer calls fc_exch_done() when done
 *          with exchange and sequence tuple.
 *      RX-inferred completion.
 *          When we receive the next sequence on the same exchange, we can
 *          retire the previous sequence ID.  (XXX not implemented).
 *      Timeout.
 *          R_A_TOV frees the sequence ID.  If we're waiting for ACK,
 *          E_D_TOV causes abort and calls upper layer response handler
 *          with FC_EX_TIMEOUT error.
 *      Receive RJT
 *          XXX defer.
 *      Send ABTS
 *          On timeout.
 *
 * The following events may occur on recipient sequences:
 *
 *      Receive
 *          Allocate sequence for first frame received.
 *          Hold during receive handler.
 *          Release when final frame received.
 *          Keep status of last N of these for the ELS RES command.  XXX TBD.
 *      Receive ABTS
 *          Deallocate sequence
 *      Send RJT
 *          Deallocate
 *
 * For now, we neglect conditions where only part of a sequence was
 * received or transmitted, or where out-of-order receipt is detected.
 */

/*
 * Locking notes:
 *
 * The EM code run in a per-CPU worker thread.
 *
 * To protect against concurrency between a worker thread code and timers,
 * sequence allocation and deallocation must be locked.
 *  - exchange refcnt can be done atomicly without locks.
 *  - sequence allocation must be locked by exch lock.
 *  - If the EM pool lock and ex_lock must be taken at the same time, then the
 *    EM pool lock must be taken before the ex_lock.
 */

/*
 * opcode names for debugging.
 */
static char *fc_exch_rctl_names[] = FC_RCTL_NAMES_INIT;

/**
 * fc_exch_name_lookup() - Lookup name by opcode
 * @op:        Opcode to be looked up
 * @table:     Opcode/name table
 * @max_index: Index not to be exceeded
 *
 * This routine is used to determine a human-readable string identifying
 * a R_CTL opcode.
 */
static inline const char *fc_exch_name_lookup(unsigned int op, char **table,
                                              unsigned int max_index)
{
        const char *name = NULL;

        if (op < max_index)
                name = table[op];
        if (!name)
                name = "unknown";
        return name;
}

/**
 * fc_exch_rctl_name() - Wrapper routine for fc_exch_name_lookup()
 * @op: The opcode to be looked up
 */
static const char *fc_exch_rctl_name(unsigned int op)
{
        return fc_exch_name_lookup(op, fc_exch_rctl_names,
                                   ARRAY_SIZE(fc_exch_rctl_names));
}

/**
 * fc_exch_hold() - Increment an exchange's reference count
 * @ep: Echange to be held
 */
static inline void fc_exch_hold(struct fc_exch *ep)
{
        atomic_inc(&ep->ex_refcnt);
}

/**
 * fc_exch_setup_hdr() - Initialize a FC header by initializing some fields
 *                       and determine SOF and EOF.
 * @ep:    The exchange to that will use the header
 * @fp:    The frame whose header is to be modified
 * @f_ctl: F_CTL bits that will be used for the frame header
 *
 * The fields initialized by this routine are: fh_ox_id, fh_rx_id,
 * fh_seq_id, fh_seq_cnt and the SOF and EOF.
 */
static void fc_exch_setup_hdr(struct fc_exch *ep, struct fc_frame *fp,
                              u32 f_ctl)
{
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        u16 fill;

        fr_sof(fp) = ep->class;
        if (ep->seq.cnt)
                fr_sof(fp) = fc_sof_normal(ep->class);

        if (f_ctl & FC_FC_END_SEQ) {
                fr_eof(fp) = FC_EOF_T;
                if (fc_sof_needs_ack(ep->class))
                        fr_eof(fp) = FC_EOF_N;
                /*
                 * From F_CTL.
                 * The number of fill bytes to make the length a 4-byte
                 * multiple is the low order 2-bits of the f_ctl.
                 * The fill itself will have been cleared by the frame
                 * allocation.
                 * After this, the length will be even, as expected by
                 * the transport.
                 */
                fill = fr_len(fp) & 3;
                if (fill) {
                        fill = 4 - fill;
                        /* TODO, this may be a problem with fragmented skb */
                        skb_put(fp_skb(fp), fill);
                        hton24(fh->fh_f_ctl, f_ctl | fill);
                }
        } else {
                WARN_ON(fr_len(fp) % 4 != 0);   /* no pad to non last frame */
                fr_eof(fp) = FC_EOF_N;
        }

        /* Initialize remaining fh fields from fc_fill_fc_hdr */
        fh->fh_ox_id = htons(ep->oxid);
        fh->fh_rx_id = htons(ep->rxid);
        fh->fh_seq_id = ep->seq.id;
        fh->fh_seq_cnt = htons(ep->seq.cnt);
}

/**
 * fc_exch_release() - Decrement an exchange's reference count
 * @ep: Exchange to be released
 *
 * If the reference count reaches zero and the exchange is complete,
 * it is freed.
 */
static void fc_exch_release(struct fc_exch *ep)
{
        struct fc_exch_mgr *mp;

        if (atomic_dec_and_test(&ep->ex_refcnt)) {
                mp = ep->em;
                if (ep->destructor)
                        ep->destructor(&ep->seq, ep->arg);
                WARN_ON(!(ep->esb_stat & ESB_ST_COMPLETE));
                mempool_free(ep, mp->ep_pool);
        }
}

/**
 * fc_exch_timer_cancel() - cancel exch timer
 * @ep:         The exchange whose timer to be canceled
 */
static inline void fc_exch_timer_cancel(struct fc_exch *ep)
{
        if (cancel_delayed_work(&ep->timeout_work)) {
                FC_EXCH_DBG(ep, "Exchange timer canceled\n");
                atomic_dec(&ep->ex_refcnt); /* drop hold for timer */
        }
}

/**
 * fc_exch_timer_set_locked() - Start a timer for an exchange w/ the
 *                              the exchange lock held
 * @ep:         The exchange whose timer will start
 * @timer_msec: The timeout period
 *
 * Used for upper level protocols to time out the exchange.
 * The timer is cancelled when it fires or when the exchange completes.
 */
static inline void fc_exch_timer_set_locked(struct fc_exch *ep,
                                            unsigned int timer_msec)
{
        if (ep->state & (FC_EX_RST_CLEANUP | FC_EX_DONE))
                return;

        FC_EXCH_DBG(ep, "Exchange timer armed : %d msecs\n", timer_msec);

        fc_exch_hold(ep);               /* hold for timer */
        if (!queue_delayed_work(fc_exch_workqueue, &ep->timeout_work,
                                msecs_to_jiffies(timer_msec)))
                fc_exch_release(ep);
}

/**
 * fc_exch_timer_set() - Lock the exchange and set the timer
 * @ep:         The exchange whose timer will start
 * @timer_msec: The timeout period
 */
static void fc_exch_timer_set(struct fc_exch *ep, unsigned int timer_msec)
{
        spin_lock_bh(&ep->ex_lock);
        fc_exch_timer_set_locked(ep, timer_msec);
        spin_unlock_bh(&ep->ex_lock);
}

/**
 * fc_exch_done_locked() - Complete an exchange with the exchange lock held
 * @ep: The exchange that is complete
 */
static int fc_exch_done_locked(struct fc_exch *ep)
{
        int rc = 1;

        /*
         * We must check for completion in case there are two threads
         * tyring to complete this. But the rrq code will reuse the
         * ep, and in that case we only clear the resp and set it as
         * complete, so it can be reused by the timer to send the rrq.
         */
        ep->resp = NULL;
        if (ep->state & FC_EX_DONE)
                return rc;
        ep->esb_stat |= ESB_ST_COMPLETE;

        if (!(ep->esb_stat & ESB_ST_REC_QUAL)) {
                ep->state |= FC_EX_DONE;
                fc_exch_timer_cancel(ep);
                rc = 0;
        }
        return rc;
}

/**
 * fc_exch_ptr_get() - Return an exchange from an exchange pool
 * @pool:  Exchange Pool to get an exchange from
 * @index: Index of the exchange within the pool
 *
 * Use the index to get an exchange from within an exchange pool. exches
 * will point to an array of exchange pointers. The index will select
 * the exchange within the array.
 */
static inline struct fc_exch *fc_exch_ptr_get(struct fc_exch_pool *pool,
                                              u16 index)
{
        struct fc_exch **exches = (struct fc_exch **)(pool + 1);
        return exches[index];
}

/**
 * fc_exch_ptr_set() - Assign an exchange to a slot in an exchange pool
 * @pool:  The pool to assign the exchange to
 * @index: The index in the pool where the exchange will be assigned
 * @ep:    The exchange to assign to the pool
 */
static inline void fc_exch_ptr_set(struct fc_exch_pool *pool, u16 index,
                                   struct fc_exch *ep)
{
        ((struct fc_exch **)(pool + 1))[index] = ep;
}

/**
 * fc_exch_delete() - Delete an exchange
 * @ep: The exchange to be deleted
 */
static void fc_exch_delete(struct fc_exch *ep)
{
        struct fc_exch_pool *pool;
        u16 index;

        pool = ep->pool;
        spin_lock_bh(&pool->lock);
        WARN_ON(pool->total_exches <= 0);
        pool->total_exches--;

        /* update cache of free slot */
        index = (ep->xid - ep->em->min_xid) >> fc_cpu_order;
        if (pool->left == FC_XID_UNKNOWN)
                pool->left = index;
        else if (pool->right == FC_XID_UNKNOWN)
                pool->right = index;
        else
                pool->next_index = index;

        fc_exch_ptr_set(pool, index, NULL);
        list_del(&ep->ex_list);
        spin_unlock_bh(&pool->lock);
        fc_exch_release(ep);    /* drop hold for exch in mp */
}

static int fc_seq_send_locked(struct fc_lport *lport, struct fc_seq *sp,
                       struct fc_frame *fp)
{
        struct fc_exch *ep;
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        int error;
        u32 f_ctl;
        u8 fh_type = fh->fh_type;

        ep = fc_seq_exch(sp);
        WARN_ON(!(ep->esb_stat & ESB_ST_SEQ_INIT));

        f_ctl = ntoh24(fh->fh_f_ctl);
        fc_exch_setup_hdr(ep, fp, f_ctl);
        fr_encaps(fp) = ep->encaps;

        /*
         * update sequence count if this frame is carrying
         * multiple FC frames when sequence offload is enabled
         * by LLD.
         */
        if (fr_max_payload(fp))
                sp->cnt += DIV_ROUND_UP((fr_len(fp) - sizeof(*fh)),
                                        fr_max_payload(fp));
        else
                sp->cnt++;

        /*
         * Send the frame.
         */
        error = lport->tt.frame_send(lport, fp);

        if (fh_type == FC_TYPE_BLS)
                goto out;

        /*
         * Update the exchange and sequence flags,
         * assuming all frames for the sequence have been sent.
         * We can only be called to send once for each sequence.
         */
        ep->f_ctl = f_ctl & ~FC_FC_FIRST_SEQ;   /* not first seq */
        if (f_ctl & FC_FC_SEQ_INIT)
                ep->esb_stat &= ~ESB_ST_SEQ_INIT;
out:
        return error;
}

/**
 * fc_seq_send() - Send a frame using existing sequence/exchange pair
 * @lport: The local port that the exchange will be sent on
 * @sp:    The sequence to be sent
 * @fp:    The frame to be sent on the exchange
 */
static int fc_seq_send(struct fc_lport *lport, struct fc_seq *sp,
                       struct fc_frame *fp)
{
        struct fc_exch *ep;
        int error;
        ep = fc_seq_exch(sp);
        spin_lock_bh(&ep->ex_lock);
        error = fc_seq_send_locked(lport, sp, fp);
        spin_unlock_bh(&ep->ex_lock);
        return error;
}

/**
 * fc_seq_alloc() - Allocate a sequence for a given exchange
 * @ep:     The exchange to allocate a new sequence for
 * @seq_id: The sequence ID to be used
 *
 * We don't support multiple originated sequences on the same exchange.
 * By implication, any previously originated sequence on this exchange
 * is complete, and we reallocate the same sequence.
 */
static struct fc_seq *fc_seq_alloc(struct fc_exch *ep, u8 seq_id)
{
        struct fc_seq *sp;

        sp = &ep->seq;
        sp->ssb_stat = 0;
        sp->cnt = 0;
        sp->id = seq_id;
        return sp;
}

/**
 * fc_seq_start_next_locked() - Allocate a new sequence on the same
 *                              exchange as the supplied sequence
 * @sp: The sequence/exchange to get a new sequence for
 */
static struct fc_seq *fc_seq_start_next_locked(struct fc_seq *sp)
{
        struct fc_exch *ep = fc_seq_exch(sp);

        sp = fc_seq_alloc(ep, ep->seq_id++);
        FC_EXCH_DBG(ep, "f_ctl %6x seq %2x\n",
                    ep->f_ctl, sp->id);
        return sp;
}

/**
 * fc_seq_start_next() - Lock the exchange and get a new sequence
 *                       for a given sequence/exchange pair
 * @sp: The sequence/exchange to get a new exchange for
 */
static struct fc_seq *fc_seq_start_next(struct fc_seq *sp)
{
        struct fc_exch *ep = fc_seq_exch(sp);

        spin_lock_bh(&ep->ex_lock);
        sp = fc_seq_start_next_locked(sp);
        spin_unlock_bh(&ep->ex_lock);

        return sp;
}

/*
 * Set the response handler for the exchange associated with a sequence.
 */
static void fc_seq_set_resp(struct fc_seq *sp,
                            void (*resp)(struct fc_seq *, struct fc_frame *,
                                         void *),
                            void *arg)
{
        struct fc_exch *ep = fc_seq_exch(sp);

        spin_lock_bh(&ep->ex_lock);
        ep->resp = resp;
        ep->arg = arg;
        spin_unlock_bh(&ep->ex_lock);
}

/**
 * fc_exch_abort_locked() - Abort an exchange
 * @ep: The exchange to be aborted
 * @timer_msec: The period of time to wait before aborting
 *
 * Locking notes:  Called with exch lock held
 *
 * Return value: 0 on success else error code
 */
static int fc_exch_abort_locked(struct fc_exch *ep,
                                unsigned int timer_msec)
{
        struct fc_seq *sp;
        struct fc_frame *fp;
        int error;

        if (ep->esb_stat & (ESB_ST_COMPLETE | ESB_ST_ABNORMAL) ||
            ep->state & (FC_EX_DONE | FC_EX_RST_CLEANUP))
                return -ENXIO;

        /*
         * Send the abort on a new sequence if possible.
         */
        sp = fc_seq_start_next_locked(&ep->seq);
        if (!sp)
                return -ENOMEM;

        ep->esb_stat |= ESB_ST_SEQ_INIT | ESB_ST_ABNORMAL;
        if (timer_msec)
                fc_exch_timer_set_locked(ep, timer_msec);

        /*
         * If not logged into the fabric, don't send ABTS but leave
         * sequence active until next timeout.
         */
        if (!ep->sid)
                return 0;

        /*
         * Send an abort for the sequence that timed out.
         */
        fp = fc_frame_alloc(ep->lp, 0);
        if (fp) {
                fc_fill_fc_hdr(fp, FC_RCTL_BA_ABTS, ep->did, ep->sid,
                               FC_TYPE_BLS, FC_FC_END_SEQ | FC_FC_SEQ_INIT, 0);
                error = fc_seq_send_locked(ep->lp, sp, fp);
        } else
                error = -ENOBUFS;
        return error;
}

/**
 * fc_seq_exch_abort() - Abort an exchange and sequence
 * @req_sp:     The sequence to be aborted
 * @timer_msec: The period of time to wait before aborting
 *
 * Generally called because of a timeout or an abort from the upper layer.
 *
 * Return value: 0 on success else error code
 */
static int fc_seq_exch_abort(const struct fc_seq *req_sp,
                             unsigned int timer_msec)
{
        struct fc_exch *ep;
        int error;

        ep = fc_seq_exch(req_sp);
        spin_lock_bh(&ep->ex_lock);
        error = fc_exch_abort_locked(ep, timer_msec);
        spin_unlock_bh(&ep->ex_lock);
        return error;
}

/**
 * fc_exch_timeout() - Handle exchange timer expiration
 * @work: The work_struct identifying the exchange that timed out
 */
static void fc_exch_timeout(struct work_struct *work)
{
        struct fc_exch *ep = container_of(work, struct fc_exch,
                                          timeout_work.work);
        struct fc_seq *sp = &ep->seq;
        void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
        void *arg;
        u32 e_stat;
        int rc = 1;

        FC_EXCH_DBG(ep, "Exchange timed out\n");

        spin_lock_bh(&ep->ex_lock);
        if (ep->state & (FC_EX_RST_CLEANUP | FC_EX_DONE))
                goto unlock;

        e_stat = ep->esb_stat;
        if (e_stat & ESB_ST_COMPLETE) {
                ep->esb_stat = e_stat & ~ESB_ST_REC_QUAL;
                spin_unlock_bh(&ep->ex_lock);
                if (e_stat & ESB_ST_REC_QUAL)
                        fc_exch_rrq(ep);
                goto done;
        } else {
                resp = ep->resp;
                arg = ep->arg;
                ep->resp = NULL;
                if (e_stat & ESB_ST_ABNORMAL)
                        rc = fc_exch_done_locked(ep);
                spin_unlock_bh(&ep->ex_lock);
                if (!rc)
                        fc_exch_delete(ep);
                if (resp)
                        resp(sp, ERR_PTR(-FC_EX_TIMEOUT), arg);
                fc_seq_exch_abort(sp, 2 * ep->r_a_tov);
                goto done;
        }
unlock:
        spin_unlock_bh(&ep->ex_lock);
done:
        /*
         * This release matches the hold taken when the timer was set.
         */
        fc_exch_release(ep);
}

/**
 * fc_exch_em_alloc() - Allocate an exchange from a specified EM.
 * @lport: The local port that the exchange is for
 * @mp:    The exchange manager that will allocate the exchange
 *
 * Returns pointer to allocated fc_exch with exch lock held.
 */
static struct fc_exch *fc_exch_em_alloc(struct fc_lport *lport,
                                        struct fc_exch_mgr *mp)
{
        struct fc_exch *ep;
        unsigned int cpu;
        u16 index;
        struct fc_exch_pool *pool;

        /* allocate memory for exchange */
        ep = mempool_alloc(mp->ep_pool, GFP_ATOMIC);
        if (!ep) {
                atomic_inc(&mp->stats.no_free_exch);
                goto out;
        }
        memset(ep, 0, sizeof(*ep));

        cpu = get_cpu();
        pool = per_cpu_ptr(mp->pool, cpu);
        spin_lock_bh(&pool->lock);
        put_cpu();

        /* peek cache of free slot */
        if (pool->left != FC_XID_UNKNOWN) {
                index = pool->left;
                pool->left = FC_XID_UNKNOWN;
                goto hit;
        }
        if (pool->right != FC_XID_UNKNOWN) {
                index = pool->right;
                pool->right = FC_XID_UNKNOWN;
                goto hit;
        }

        index = pool->next_index;
        /* allocate new exch from pool */
        while (fc_exch_ptr_get(pool, index)) {
                index = index == mp->pool_max_index ? 0 : index + 1;
                if (index == pool->next_index)
                        goto err;
        }
        pool->next_index = index == mp->pool_max_index ? 0 : index + 1;
hit:
        fc_exch_hold(ep);       /* hold for exch in mp */
        spin_lock_init(&ep->ex_lock);
        /*
         * Hold exch lock for caller to prevent fc_exch_reset()
         * from releasing exch  while fc_exch_alloc() caller is
         * still working on exch.
         */
        spin_lock_bh(&ep->ex_lock);

        fc_exch_ptr_set(pool, index, ep);
        list_add_tail(&ep->ex_list, &pool->ex_list);
        fc_seq_alloc(ep, ep->seq_id++);
        pool->total_exches++;
        spin_unlock_bh(&pool->lock);

        /*
         *  update exchange
         */
        ep->oxid = ep->xid = (index << fc_cpu_order | cpu) + mp->min_xid;
        ep->em = mp;
        ep->pool = pool;
        ep->lp = lport;
        ep->f_ctl = FC_FC_FIRST_SEQ;    /* next seq is first seq */
        ep->rxid = FC_XID_UNKNOWN;
        ep->class = mp->class;
        INIT_DELAYED_WORK(&ep->timeout_work, fc_exch_timeout);
out:
        return ep;
err:
        spin_unlock_bh(&pool->lock);
        atomic_inc(&mp->stats.no_free_exch_xid);
        mempool_free(ep, mp->ep_pool);
        return NULL;
}

/**
 * fc_exch_alloc() - Allocate an exchange from an EM on a
 *                   local port's list of EMs.
 * @lport: The local port that will own the exchange
 * @fp:    The FC frame that the exchange will be for
 *
 * This function walks the list of exchange manager(EM)
 * anchors to select an EM for a new exchange allocation. The
 * EM is selected when a NULL match function pointer is encountered
 * or when a call to a match function returns true.
 */
static inline struct fc_exch *fc_exch_alloc(struct fc_lport *lport,
                                            struct fc_frame *fp)
{
        struct fc_exch_mgr_anchor *ema;

        list_for_each_entry(ema, &lport->ema_list, ema_list)
                if (!ema->match || ema->match(fp))
                        return fc_exch_em_alloc(lport, ema->mp);
        return NULL;
}

/**
 * fc_exch_find() - Lookup and hold an exchange
 * @mp:  The exchange manager to lookup the exchange from
 * @xid: The XID of the exchange to look up
 */
static struct fc_exch *fc_exch_find(struct fc_exch_mgr *mp, u16 xid)
{
        struct fc_exch_pool *pool;
        struct fc_exch *ep = NULL;

        if ((xid >= mp->min_xid) && (xid <= mp->max_xid)) {
                pool = per_cpu_ptr(mp->pool, xid & fc_cpu_mask);
                spin_lock_bh(&pool->lock);
                ep = fc_exch_ptr_get(pool, (xid - mp->min_xid) >> fc_cpu_order);
                if (ep) {
                        WARN_ON(ep->xid != xid);
                        fc_exch_hold(ep);
                }
                spin_unlock_bh(&pool->lock);
        }
        return ep;
}


/**
 * fc_exch_done() - Indicate that an exchange/sequence tuple is complete and
 *                  the memory allocated for the related objects may be freed.
 * @sp: The sequence that has completed
 */
static void fc_exch_done(struct fc_seq *sp)
{
        struct fc_exch *ep = fc_seq_exch(sp);
        int rc;

        spin_lock_bh(&ep->ex_lock);
        rc = fc_exch_done_locked(ep);
        spin_unlock_bh(&ep->ex_lock);
        if (!rc)
                fc_exch_delete(ep);
}

/**
 * fc_exch_resp() - Allocate a new exchange for a response frame
 * @lport: The local port that the exchange was for
 * @mp:    The exchange manager to allocate the exchange from
 * @fp:    The response frame
 *
 * Sets the responder ID in the frame header.
 */
static struct fc_exch *fc_exch_resp(struct fc_lport *lport,
                                    struct fc_exch_mgr *mp,
                                    struct fc_frame *fp)
{
        struct fc_exch *ep;
        struct fc_frame_header *fh;

        ep = fc_exch_alloc(lport, fp);
        if (ep) {
                ep->class = fc_frame_class(fp);

                /*
                 * Set EX_CTX indicating we're responding on this exchange.
                 */
                ep->f_ctl |= FC_FC_EX_CTX;      /* we're responding */
                ep->f_ctl &= ~FC_FC_FIRST_SEQ;  /* not new */
                fh = fc_frame_header_get(fp);
                ep->sid = ntoh24(fh->fh_d_id);
                ep->did = ntoh24(fh->fh_s_id);
                ep->oid = ep->did;

                /*
                 * Allocated exchange has placed the XID in the
                 * originator field. Move it to the responder field,
                 * and set the originator XID from the frame.
                 */
                ep->rxid = ep->xid;
                ep->oxid = ntohs(fh->fh_ox_id);
                ep->esb_stat |= ESB_ST_RESP | ESB_ST_SEQ_INIT;
                if ((ntoh24(fh->fh_f_ctl) & FC_FC_SEQ_INIT) == 0)
                        ep->esb_stat &= ~ESB_ST_SEQ_INIT;

                fc_exch_hold(ep);       /* hold for caller */
                spin_unlock_bh(&ep->ex_lock);   /* lock from fc_exch_alloc */
        }
        return ep;
}

/**
 * fc_seq_lookup_recip() - Find a sequence where the other end
 *                         originated the sequence
 * @lport: The local port that the frame was sent to
 * @mp:    The Exchange Manager to lookup the exchange from
 * @fp:    The frame associated with the sequence we're looking for
 *
 * If fc_pf_rjt_reason is FC_RJT_NONE then this function will have a hold
 * on the ep that should be released by the caller.
 */
static enum fc_pf_rjt_reason fc_seq_lookup_recip(struct fc_lport *lport,
                                                 struct fc_exch_mgr *mp,
                                                 struct fc_frame *fp)
{
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        struct fc_exch *ep = NULL;
        struct fc_seq *sp = NULL;
        enum fc_pf_rjt_reason reject = FC_RJT_NONE;
        u32 f_ctl;
        u16 xid;

        f_ctl = ntoh24(fh->fh_f_ctl);
        WARN_ON((f_ctl & FC_FC_SEQ_CTX) != 0);

        /*
         * Lookup or create the exchange if we will be creating the sequence.
         */
        if (f_ctl & FC_FC_EX_CTX) {
                xid = ntohs(fh->fh_ox_id);      /* we originated exch */
                ep = fc_exch_find(mp, xid);
                if (!ep) {
                        atomic_inc(&mp->stats.xid_not_found);
                        reject = FC_RJT_OX_ID;
                        goto out;
                }
                if (ep->rxid == FC_XID_UNKNOWN)
                        ep->rxid = ntohs(fh->fh_rx_id);
                else if (ep->rxid != ntohs(fh->fh_rx_id)) {
                        reject = FC_RJT_OX_ID;
                        goto rel;
                }
        } else {
                xid = ntohs(fh->fh_rx_id);      /* we are the responder */

                /*
                 * Special case for MDS issuing an ELS TEST with a
                 * bad rxid of 0.
                 * XXX take this out once we do the proper reject.
                 */
                if (xid == 0 && fh->fh_r_ctl == FC_RCTL_ELS_REQ &&
                    fc_frame_payload_op(fp) == ELS_TEST) {
                        fh->fh_rx_id = htons(FC_XID_UNKNOWN);
                        xid = FC_XID_UNKNOWN;
                }

                /*
                 * new sequence - find the exchange
                 */
                ep = fc_exch_find(mp, xid);
                if ((f_ctl & FC_FC_FIRST_SEQ) && fc_sof_is_init(fr_sof(fp))) {
                        if (ep) {
                                atomic_inc(&mp->stats.xid_busy);
                                reject = FC_RJT_RX_ID;
                                goto rel;
                        }
                        ep = fc_exch_resp(lport, mp, fp);
                        if (!ep) {
                                reject = FC_RJT_EXCH_EST;       /* XXX */
                                goto out;
                        }
                        xid = ep->xid;  /* get our XID */
                } else if (!ep) {
                        atomic_inc(&mp->stats.xid_not_found);
                        reject = FC_RJT_RX_ID;  /* XID not found */
                        goto out;
                }
        }

        /*
         * At this point, we have the exchange held.
         * Find or create the sequence.
         */
        if (fc_sof_is_init(fr_sof(fp))) {
                sp = &ep->seq;
                sp->ssb_stat |= SSB_ST_RESP;
                sp->id = fh->fh_seq_id;
        } else {
                sp = &ep->seq;
                if (sp->id != fh->fh_seq_id) {
                        atomic_inc(&mp->stats.seq_not_found);
                        if (f_ctl & FC_FC_END_SEQ) {
                                /*
                                 * Update sequence_id based on incoming last
                                 * frame of sequence exchange. This is needed
                                 * for FC target where DDP has been used
                                 * on target where, stack is indicated only
                                 * about last frame's (payload _header) header.
                                 * Whereas "seq_id" which is part of
                                 * frame_header is allocated by initiator
                                 * which is totally different from "seq_id"
                                 * allocated when XFER_RDY was sent by target.
                                 * To avoid false -ve which results into not
                                 * sending RSP, hence write request on other
                                 * end never finishes.
                                 */
                                spin_lock_bh(&ep->ex_lock);
                                sp->ssb_stat |= SSB_ST_RESP;
                                sp->id = fh->fh_seq_id;
                                spin_unlock_bh(&ep->ex_lock);
                        } else {
                                /* sequence/exch should exist */
                                reject = FC_RJT_SEQ_ID;
                                goto rel;
                        }
                }
        }
        WARN_ON(ep != fc_seq_exch(sp));

        if (f_ctl & FC_FC_SEQ_INIT)
                ep->esb_stat |= ESB_ST_SEQ_INIT;

        fr_seq(fp) = sp;
out:
        return reject;
rel:
        fc_exch_done(&ep->seq);
        fc_exch_release(ep);    /* hold from fc_exch_find/fc_exch_resp */
        return reject;
}

/**
 * fc_seq_lookup_orig() - Find a sequence where this end
 *                        originated the sequence
 * @mp:    The Exchange Manager to lookup the exchange from
 * @fp:    The frame associated with the sequence we're looking for
 *
 * Does not hold the sequence for the caller.
 */
static struct fc_seq *fc_seq_lookup_orig(struct fc_exch_mgr *mp,
                                         struct fc_frame *fp)
{
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        struct fc_exch *ep;
        struct fc_seq *sp = NULL;
        u32 f_ctl;
        u16 xid;

        f_ctl = ntoh24(fh->fh_f_ctl);
        WARN_ON((f_ctl & FC_FC_SEQ_CTX) != FC_FC_SEQ_CTX);
        xid = ntohs((f_ctl & FC_FC_EX_CTX) ? fh->fh_ox_id : fh->fh_rx_id);
        ep = fc_exch_find(mp, xid);
        if (!ep)
                return NULL;
        if (ep->seq.id == fh->fh_seq_id) {
                /*
                 * Save the RX_ID if we didn't previously know it.
                 */
                sp = &ep->seq;
                if ((f_ctl & FC_FC_EX_CTX) != 0 &&
                    ep->rxid == FC_XID_UNKNOWN) {
                        ep->rxid = ntohs(fh->fh_rx_id);
                }
        }
        fc_exch_release(ep);
        return sp;
}

/**
 * fc_exch_set_addr() - Set the source and destination IDs for an exchange
 * @ep:      The exchange to set the addresses for
 * @orig_id: The originator's ID
 * @resp_id: The responder's ID
 *
 * Note this must be done before the first sequence of the exchange is sent.
 */
static void fc_exch_set_addr(struct fc_exch *ep,
                             u32 orig_id, u32 resp_id)
{
        ep->oid = orig_id;
        if (ep->esb_stat & ESB_ST_RESP) {
                ep->sid = resp_id;
                ep->did = orig_id;
        } else {
                ep->sid = orig_id;
                ep->did = resp_id;
        }
}

/**
 * fc_seq_els_rsp_send() - Send an ELS response using information from
 *                         the existing sequence/exchange.
 * @fp:       The received frame
 * @els_cmd:  The ELS command to be sent
 * @els_data: The ELS data to be sent
 *
 * The received frame is not freed.
 */
static void fc_seq_els_rsp_send(struct fc_frame *fp, enum fc_els_cmd els_cmd,
                                struct fc_seq_els_data *els_data)
{
        switch (els_cmd) {
        case ELS_LS_RJT:
                fc_seq_ls_rjt(fp, els_data->reason, els_data->explan);
                break;
        case ELS_LS_ACC:
                fc_seq_ls_acc(fp);
                break;
        case ELS_RRQ:
                fc_exch_els_rrq(fp);
                break;
        case ELS_REC:
                fc_exch_els_rec(fp);
                break;
        default:
                FC_LPORT_DBG(fr_dev(fp), "Invalid ELS CMD:%x\n", els_cmd);
        }
}

/**
 * fc_seq_send_last() - Send a sequence that is the last in the exchange
 * @sp:      The sequence that is to be sent
 * @fp:      The frame that will be sent on the sequence
 * @rctl:    The R_CTL information to be sent
 * @fh_type: The frame header type
 */
static void fc_seq_send_last(struct fc_seq *sp, struct fc_frame *fp,
                             enum fc_rctl rctl, enum fc_fh_type fh_type)
{
        u32 f_ctl;
        struct fc_exch *ep = fc_seq_exch(sp);

        f_ctl = FC_FC_LAST_SEQ | FC_FC_END_SEQ | FC_FC_SEQ_INIT;
        f_ctl |= ep->f_ctl;
        fc_fill_fc_hdr(fp, rctl, ep->did, ep->sid, fh_type, f_ctl, 0);
        fc_seq_send_locked(ep->lp, sp, fp);
}

/**
 * fc_seq_send_ack() - Send an acknowledgement that we've received a frame
 * @sp:    The sequence to send the ACK on
 * @rx_fp: The received frame that is being acknoledged
 *
 * Send ACK_1 (or equiv.) indicating we received something.
 */
static void fc_seq_send_ack(struct fc_seq *sp, const struct fc_frame *rx_fp)
{
        struct fc_frame *fp;
        struct fc_frame_header *rx_fh;
        struct fc_frame_header *fh;
        struct fc_exch *ep = fc_seq_exch(sp);
        struct fc_lport *lport = ep->lp;
        unsigned int f_ctl;

        /*
         * Don't send ACKs for class 3.
         */
        if (fc_sof_needs_ack(fr_sof(rx_fp))) {
                fp = fc_frame_alloc(lport, 0);
                if (!fp)
                        return;

                fh = fc_frame_header_get(fp);
                fh->fh_r_ctl = FC_RCTL_ACK_1;
                fh->fh_type = FC_TYPE_BLS;

                /*
                 * Form f_ctl by inverting EX_CTX and SEQ_CTX (bits 23, 22).
                 * Echo FIRST_SEQ, LAST_SEQ, END_SEQ, END_CONN, SEQ_INIT.
                 * Bits 9-8 are meaningful (retransmitted or unidirectional).
                 * Last ACK uses bits 7-6 (continue sequence),
                 * bits 5-4 are meaningful (what kind of ACK to use).
                 */
                rx_fh = fc_frame_header_get(rx_fp);
                f_ctl = ntoh24(rx_fh->fh_f_ctl);
                f_ctl &= FC_FC_EX_CTX | FC_FC_SEQ_CTX |
                        FC_FC_FIRST_SEQ | FC_FC_LAST_SEQ |
                        FC_FC_END_SEQ | FC_FC_END_CONN | FC_FC_SEQ_INIT |
                        FC_FC_RETX_SEQ | FC_FC_UNI_TX;
                f_ctl ^= FC_FC_EX_CTX | FC_FC_SEQ_CTX;
                hton24(fh->fh_f_ctl, f_ctl);

                fc_exch_setup_hdr(ep, fp, f_ctl);
                fh->fh_seq_id = rx_fh->fh_seq_id;
                fh->fh_seq_cnt = rx_fh->fh_seq_cnt;
                fh->fh_parm_offset = htonl(1);  /* ack single frame */

                fr_sof(fp) = fr_sof(rx_fp);
                if (f_ctl & FC_FC_END_SEQ)
                        fr_eof(fp) = FC_EOF_T;
                else
                        fr_eof(fp) = FC_EOF_N;

                lport->tt.frame_send(lport, fp);
        }
}

/**
 * fc_exch_send_ba_rjt() - Send BLS Reject
 * @rx_fp:  The frame being rejected
 * @reason: The reason the frame is being rejected
 * @explan: The explanation for the rejection
 *
 * This is for rejecting BA_ABTS only.
 */
static void fc_exch_send_ba_rjt(struct fc_frame *rx_fp,
                                enum fc_ba_rjt_reason reason,
                                enum fc_ba_rjt_explan explan)
{
        struct fc_frame *fp;
        struct fc_frame_header *rx_fh;
        struct fc_frame_header *fh;
        struct fc_ba_rjt *rp;
        struct fc_lport *lport;
        unsigned int f_ctl;

        lport = fr_dev(rx_fp);
        fp = fc_frame_alloc(lport, sizeof(*rp));
        if (!fp)
                return;
        fh = fc_frame_header_get(fp);
        rx_fh = fc_frame_header_get(rx_fp);

        memset(fh, 0, sizeof(*fh) + sizeof(*rp));

        rp = fc_frame_payload_get(fp, sizeof(*rp));
        rp->br_reason = reason;
        rp->br_explan = explan;

        /*
         * seq_id, cs_ctl, df_ctl and param/offset are zero.
         */
        memcpy(fh->fh_s_id, rx_fh->fh_d_id, 3);
        memcpy(fh->fh_d_id, rx_fh->fh_s_id, 3);
        fh->fh_ox_id = rx_fh->fh_ox_id;
        fh->fh_rx_id = rx_fh->fh_rx_id;
        fh->fh_seq_cnt = rx_fh->fh_seq_cnt;
        fh->fh_r_ctl = FC_RCTL_BA_RJT;
        fh->fh_type = FC_TYPE_BLS;

        /*
         * Form f_ctl by inverting EX_CTX and SEQ_CTX (bits 23, 22).
         * Echo FIRST_SEQ, LAST_SEQ, END_SEQ, END_CONN, SEQ_INIT.
         * Bits 9-8 are meaningful (retransmitted or unidirectional).
         * Last ACK uses bits 7-6 (continue sequence),
         * bits 5-4 are meaningful (what kind of ACK to use).
         * Always set LAST_SEQ, END_SEQ.
         */
        f_ctl = ntoh24(rx_fh->fh_f_ctl);
        f_ctl &= FC_FC_EX_CTX | FC_FC_SEQ_CTX |
                FC_FC_END_CONN | FC_FC_SEQ_INIT |
                FC_FC_RETX_SEQ | FC_FC_UNI_TX;
        f_ctl ^= FC_FC_EX_CTX | FC_FC_SEQ_CTX;
        f_ctl |= FC_FC_LAST_SEQ | FC_FC_END_SEQ;
        f_ctl &= ~FC_FC_FIRST_SEQ;
        hton24(fh->fh_f_ctl, f_ctl);

        fr_sof(fp) = fc_sof_class(fr_sof(rx_fp));
        fr_eof(fp) = FC_EOF_T;
        if (fc_sof_needs_ack(fr_sof(fp)))
                fr_eof(fp) = FC_EOF_N;

        lport->tt.frame_send(lport, fp);
}

/**
 * fc_exch_recv_abts() - Handle an incoming ABTS
 * @ep:    The exchange the abort was on
 * @rx_fp: The ABTS frame
 *
 * This would be for target mode usually, but could be due to lost
 * FCP transfer ready, confirm or RRQ. We always handle this as an
 * exchange abort, ignoring the parameter.
 */
static void fc_exch_recv_abts(struct fc_exch *ep, struct fc_frame *rx_fp)
{
        struct fc_frame *fp;
        struct fc_ba_acc *ap;
        struct fc_frame_header *fh;
        struct fc_seq *sp;

        if (!ep)
                goto reject;
        spin_lock_bh(&ep->ex_lock);
        if (ep->esb_stat & ESB_ST_COMPLETE) {
                spin_unlock_bh(&ep->ex_lock);
                goto reject;
        }
        if (!(ep->esb_stat & ESB_ST_REC_QUAL))
                fc_exch_hold(ep);               /* hold for REC_QUAL */
        ep->esb_stat |= ESB_ST_ABNORMAL | ESB_ST_REC_QUAL;
        fc_exch_timer_set_locked(ep, ep->r_a_tov);

        fp = fc_frame_alloc(ep->lp, sizeof(*ap));
        if (!fp) {
                spin_unlock_bh(&ep->ex_lock);
                goto free;
        }
        fh = fc_frame_header_get(fp);
        ap = fc_frame_payload_get(fp, sizeof(*ap));
        memset(ap, 0, sizeof(*ap));
        sp = &ep->seq;
        ap->ba_high_seq_cnt = htons(0xffff);
        if (sp->ssb_stat & SSB_ST_RESP) {
                ap->ba_seq_id = sp->id;
                ap->ba_seq_id_val = FC_BA_SEQ_ID_VAL;
                ap->ba_high_seq_cnt = fh->fh_seq_cnt;
                ap->ba_low_seq_cnt = htons(sp->cnt);
        }
        sp = fc_seq_start_next_locked(sp);
        fc_seq_send_last(sp, fp, FC_RCTL_BA_ACC, FC_TYPE_BLS);
        spin_unlock_bh(&ep->ex_lock);
        fc_frame_free(rx_fp);
        return;

reject:
        fc_exch_send_ba_rjt(rx_fp, FC_BA_RJT_UNABLE, FC_BA_RJT_INV_XID);
free:
        fc_frame_free(rx_fp);
}

/**
 * fc_seq_assign() - Assign exchange and sequence for incoming request
 * @lport: The local port that received the request
 * @fp:    The request frame
 *
 * On success, the sequence pointer will be returned and also in fr_seq(@fp).
 * A reference will be held on the exchange/sequence for the caller, which
 * must call fc_seq_release().
 */
static struct fc_seq *fc_seq_assign(struct fc_lport *lport, struct fc_frame *fp)
{
        struct fc_exch_mgr_anchor *ema;

        WARN_ON(lport != fr_dev(fp));
        WARN_ON(fr_seq(fp));
        fr_seq(fp) = NULL;

        list_for_each_entry(ema, &lport->ema_list, ema_list)
                if ((!ema->match || ema->match(fp)) &&
                    fc_seq_lookup_recip(lport, ema->mp, fp) == FC_RJT_NONE)
                        break;
        return fr_seq(fp);
}

/**
 * fc_seq_release() - Release the hold
 * @sp:    The sequence.
 */
static void fc_seq_release(struct fc_seq *sp)
{
        fc_exch_release(fc_seq_exch(sp));
}

/**
 * fc_exch_recv_req() - Handler for an incoming request
 * @lport: The local port that received the request
 * @mp:    The EM that the exchange is on
 * @fp:    The request frame
 *
 * This is used when the other end is originating the exchange
 * and the sequence.
 */
static void fc_exch_recv_req(struct fc_lport *lport, struct fc_exch_mgr *mp,
                             struct fc_frame *fp)
{
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        struct fc_seq *sp = NULL;
        struct fc_exch *ep = NULL;
        enum fc_pf_rjt_reason reject;

        /* We can have the wrong fc_lport at this point with NPIV, which is a
         * problem now that we know a new exchange needs to be allocated
         */
        lport = fc_vport_id_lookup(lport, ntoh24(fh->fh_d_id));
        if (!lport) {
                fc_frame_free(fp);
                return;
        }
        fr_dev(fp) = lport;

        BUG_ON(fr_seq(fp));             /* XXX remove later */

        /*
         * If the RX_ID is 0xffff, don't allocate an exchange.
         * The upper-level protocol may request one later, if needed.
         */
        if (fh->fh_rx_id == htons(FC_XID_UNKNOWN))
                return lport->tt.lport_recv(lport, fp);

        reject = fc_seq_lookup_recip(lport, mp, fp);
        if (reject == FC_RJT_NONE) {
                sp = fr_seq(fp);        /* sequence will be held */
                ep = fc_seq_exch(sp);
                fc_seq_send_ack(sp, fp);
                ep->encaps = fr_encaps(fp);

                /*
                 * Call the receive function.
                 *
                 * The receive function may allocate a new sequence
                 * over the old one, so we shouldn't change the
                 * sequence after this.
                 *
                 * The frame will be freed by the receive function.
                 * If new exch resp handler is valid then call that
                 * first.
                 */
                if (ep->resp)
                        ep->resp(sp, fp, ep->arg);
                else
                        lport->tt.lport_recv(lport, fp);
                fc_exch_release(ep);    /* release from lookup */
        } else {
                FC_LPORT_DBG(lport, "exch/seq lookup failed: reject %x\n",
                             reject);
                fc_frame_free(fp);
        }
}

/**
 * fc_exch_recv_seq_resp() - Handler for an incoming response where the other
 *                           end is the originator of the sequence that is a
 *                           response to our initial exchange
 * @mp: The EM that the exchange is on
 * @fp: The response frame
 */
static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        struct fc_seq *sp;
        struct fc_exch *ep;
        enum fc_sof sof;
        u32 f_ctl;
        void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
        void *ex_resp_arg;
        int rc;

        ep = fc_exch_find(mp, ntohs(fh->fh_ox_id));
        if (!ep) {
                atomic_inc(&mp->stats.xid_not_found);
                goto out;
        }
        if (ep->esb_stat & ESB_ST_COMPLETE) {
                atomic_inc(&mp->stats.xid_not_found);
                goto rel;
        }
        if (ep->rxid == FC_XID_UNKNOWN)
                ep->rxid = ntohs(fh->fh_rx_id);
        if (ep->sid != 0 && ep->sid != ntoh24(fh->fh_d_id)) {
                atomic_inc(&mp->stats.xid_not_found);
                goto rel;
        }
        if (ep->did != ntoh24(fh->fh_s_id) &&
            ep->did != FC_FID_FLOGI) {
                atomic_inc(&mp->stats.xid_not_found);
                goto rel;
        }
        sof = fr_sof(fp);
        sp = &ep->seq;
        if (fc_sof_is_init(sof)) {
                sp->ssb_stat |= SSB_ST_RESP;
                sp->id = fh->fh_seq_id;
        } else if (sp->id != fh->fh_seq_id) {
                atomic_inc(&mp->stats.seq_not_found);
                goto rel;
        }

        f_ctl = ntoh24(fh->fh_f_ctl);
        fr_seq(fp) = sp;
        if (f_ctl & FC_FC_SEQ_INIT)
                ep->esb_stat |= ESB_ST_SEQ_INIT;

        if (fc_sof_needs_ack(sof))
                fc_seq_send_ack(sp, fp);
        resp = ep->resp;
        ex_resp_arg = ep->arg;

        if (fh->fh_type != FC_TYPE_FCP && fr_eof(fp) == FC_EOF_T &&
            (f_ctl & (FC_FC_LAST_SEQ | FC_FC_END_SEQ)) ==
            (FC_FC_LAST_SEQ | FC_FC_END_SEQ)) {
                spin_lock_bh(&ep->ex_lock);
                resp = ep->resp;
                rc = fc_exch_done_locked(ep);
                WARN_ON(fc_seq_exch(sp) != ep);
                spin_unlock_bh(&ep->ex_lock);
                if (!rc)
                        fc_exch_delete(ep);
        }

        /*
         * Call the receive function.
         * The sequence is held (has a refcnt) for us,
         * but not for the receive function.
         *
         * The receive function may allocate a new sequence
         * over the old one, so we shouldn't change the
         * sequence after this.
         *
         * The frame will be freed by the receive function.
         * If new exch resp handler is valid then call that
         * first.
         */
        if (resp)
                resp(sp, fp, ex_resp_arg);
        else
                fc_frame_free(fp);
        fc_exch_release(ep);
        return;
rel:
        fc_exch_release(ep);
out:
        fc_frame_free(fp);
}

/**
 * fc_exch_recv_resp() - Handler for a sequence where other end is
 *                       responding to our sequence
 * @mp: The EM that the exchange is on
 * @fp: The response frame
 */
static void fc_exch_recv_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
        struct fc_seq *sp;

        sp = fc_seq_lookup_orig(mp, fp);        /* doesn't hold sequence */

        if (!sp)
                atomic_inc(&mp->stats.xid_not_found);
        else
                atomic_inc(&mp->stats.non_bls_resp);

        fc_frame_free(fp);
}

/**
 * fc_exch_abts_resp() - Handler for a response to an ABT
 * @ep: The exchange that the frame is on
 * @fp: The response frame
 *
 * This response would be to an ABTS cancelling an exchange or sequence.
 * The response can be either BA_ACC or BA_RJT
 */
static void fc_exch_abts_resp(struct fc_exch *ep, struct fc_frame *fp)
{
        void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
        void *ex_resp_arg;
        struct fc_frame_header *fh;
        struct fc_ba_acc *ap;
        struct fc_seq *sp;
        u16 low;
        u16 high;
        int rc = 1, has_rec = 0;

        fh = fc_frame_header_get(fp);
        FC_EXCH_DBG(ep, "exch: BLS rctl %x - %s\n", fh->fh_r_ctl,
                    fc_exch_rctl_name(fh->fh_r_ctl));

        if (cancel_delayed_work_sync(&ep->timeout_work)) {
                FC_EXCH_DBG(ep, "Exchange timer canceled due to ABTS response\n");
                fc_exch_release(ep);    /* release from pending timer hold */
        }

        spin_lock_bh(&ep->ex_lock);
        switch (fh->fh_r_ctl) {
        case FC_RCTL_BA_ACC:
                ap = fc_frame_payload_get(fp, sizeof(*ap));
                if (!ap)
                        break;

                /*
                 * Decide whether to establish a Recovery Qualifier.
                 * We do this if there is a non-empty SEQ_CNT range and
                 * SEQ_ID is the same as the one we aborted.
                 */
                low = ntohs(ap->ba_low_seq_cnt);
                high = ntohs(ap->ba_high_seq_cnt);
                if ((ep->esb_stat & ESB_ST_REC_QUAL) == 0 &&
                    (ap->ba_seq_id_val != FC_BA_SEQ_ID_VAL ||
                     ap->ba_seq_id == ep->seq_id) && low != high) {
                        ep->esb_stat |= ESB_ST_REC_QUAL;
                        fc_exch_hold(ep);  /* hold for recovery qualifier */
                        has_rec = 1;
                }
                break;
        case FC_RCTL_BA_RJT:
                break;
        default:
                break;
        }

        resp = ep->resp;
        ex_resp_arg = ep->arg;

        /* do we need to do some other checks here. Can we reuse more of
         * fc_exch_recv_seq_resp
         */
        sp = &ep->seq;
        /*
         * do we want to check END_SEQ as well as LAST_SEQ here?
         */
        if (ep->fh_type != FC_TYPE_FCP &&
            ntoh24(fh->fh_f_ctl) & FC_FC_LAST_SEQ)
                rc = fc_exch_done_locked(ep);
        spin_unlock_bh(&ep->ex_lock);
        if (!rc)
                fc_exch_delete(ep);

        if (resp)
                resp(sp, fp, ex_resp_arg);
        else
                fc_frame_free(fp);

        if (has_rec)
                fc_exch_timer_set(ep, ep->r_a_tov);

}

/**
 * fc_exch_recv_bls() - Handler for a BLS sequence
 * @mp: The EM that the exchange is on
 * @fp: The request frame
 *
 * The BLS frame is always a sequence initiated by the remote side.
 * We may be either the originator or recipient of the exchange.
 */
static void fc_exch_recv_bls(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
        struct fc_frame_header *fh;
        struct fc_exch *ep;
        u32 f_ctl;

        fh = fc_frame_header_get(fp);
        f_ctl = ntoh24(fh->fh_f_ctl);
        fr_seq(fp) = NULL;

        ep = fc_exch_find(mp, (f_ctl & FC_FC_EX_CTX) ?
                          ntohs(fh->fh_ox_id) : ntohs(fh->fh_rx_id));
        if (ep && (f_ctl & FC_FC_SEQ_INIT)) {
                spin_lock_bh(&ep->ex_lock);
                ep->esb_stat |= ESB_ST_SEQ_INIT;
                spin_unlock_bh(&ep->ex_lock);
        }
        if (f_ctl & FC_FC_SEQ_CTX) {
                /*
                 * A response to a sequence we initiated.
                 * This should only be ACKs for class 2 or F.
                 */
                switch (fh->fh_r_ctl) {
                case FC_RCTL_ACK_1:
                case FC_RCTL_ACK_0:
                        break;
                default:
                        if (ep)
                                FC_EXCH_DBG(ep, "BLS rctl %x - %s received\n",
                                            fh->fh_r_ctl,
                                            fc_exch_rctl_name(fh->fh_r_ctl));
                        break;
                }
                fc_frame_free(fp);
        } else {
                switch (fh->fh_r_ctl) {
                case FC_RCTL_BA_RJT:
                case FC_RCTL_BA_ACC:
                        if (ep)
                                fc_exch_abts_resp(ep, fp);
                        else
                                fc_frame_free(fp);
                        break;
                case FC_RCTL_BA_ABTS:
                        fc_exch_recv_abts(ep, fp);
                        break;
                default:                        /* ignore junk */
                        fc_frame_free(fp);
                        break;
                }
        }
        if (ep)
                fc_exch_release(ep);    /* release hold taken by fc_exch_find */
}

/**
 * fc_seq_ls_acc() - Accept sequence with LS_ACC
 * @rx_fp: The received frame, not freed here.
 *
 * If this fails due to allocation or transmit congestion, assume the
 * originator will repeat the sequence.
 */
static void fc_seq_ls_acc(struct fc_frame *rx_fp)
{
        struct fc_lport *lport;
        struct fc_els_ls_acc *acc;
        struct fc_frame *fp;

        lport = fr_dev(rx_fp);
        fp = fc_frame_alloc(lport, sizeof(*acc));
        if (!fp)
                return;
        acc = fc_frame_payload_get(fp, sizeof(*acc));
        memset(acc, 0, sizeof(*acc));
        acc->la_cmd = ELS_LS_ACC;
        fc_fill_reply_hdr(fp, rx_fp, FC_RCTL_ELS_REP, 0);
        lport->tt.frame_send(lport, fp);
}

/**
 * fc_seq_ls_rjt() - Reject a sequence with ELS LS_RJT
 * @rx_fp: The received frame, not freed here.
 * @reason: The reason the sequence is being rejected
 * @explan: The explanation for the rejection
 *
 * If this fails due to allocation or transmit congestion, assume the
 * originator will repeat the sequence.
 */
static void fc_seq_ls_rjt(struct fc_frame *rx_fp, enum fc_els_rjt_reason reason,
                          enum fc_els_rjt_explan explan)
{
        struct fc_lport *lport;
        struct fc_els_ls_rjt *rjt;
        struct fc_frame *fp;

        lport = fr_dev(rx_fp);
        fp = fc_frame_alloc(lport, sizeof(*rjt));
        if (!fp)
                return;
        rjt = fc_frame_payload_get(fp, sizeof(*rjt));
        memset(rjt, 0, sizeof(*rjt));
        rjt->er_cmd = ELS_LS_RJT;
        rjt->er_reason = reason;
        rjt->er_explan = explan;
        fc_fill_reply_hdr(fp, rx_fp, FC_RCTL_ELS_REP, 0);
        lport->tt.frame_send(lport, fp);
}

/**
 * fc_exch_reset() - Reset an exchange
 * @ep: The exchange to be reset
 */
static void fc_exch_reset(struct fc_exch *ep)
{
        struct fc_seq *sp;
        void (*resp)(struct fc_seq *, struct fc_frame *, void *);
        void *arg;
        int rc = 1;

        spin_lock_bh(&ep->ex_lock);
        fc_exch_abort_locked(ep, 0);
        ep->state |= FC_EX_RST_CLEANUP;
        fc_exch_timer_cancel(ep);
        resp = ep->resp;
        ep->resp = NULL;
        if (ep->esb_stat & ESB_ST_REC_QUAL)
                atomic_dec(&ep->ex_refcnt);     /* drop hold for rec_qual */
        ep->esb_stat &= ~ESB_ST_REC_QUAL;
        arg = ep->arg;
        sp = &ep->seq;
        rc = fc_exch_done_locked(ep);
        spin_unlock_bh(&ep->ex_lock);
        if (!rc)
                fc_exch_delete(ep);

        if (resp)
                resp(sp, ERR_PTR(-FC_EX_CLOSED), arg);
}

/**
 * fc_exch_pool_reset() - Reset a per cpu exchange pool
 * @lport: The local port that the exchange pool is on
 * @pool:  The exchange pool to be reset
 * @sid:   The source ID
 * @did:   The destination ID
 *
 * Resets a per cpu exches pool, releasing all of its sequences
 * and exchanges. If sid is non-zero then reset only exchanges
 * we sourced from the local port's FID. If did is non-zero then
 * only reset exchanges destined for the local port's FID.
 */
static void fc_exch_pool_reset(struct fc_lport *lport,
                               struct fc_exch_pool *pool,
                               u32 sid, u32 did)
{
        struct fc_exch *ep;
        struct fc_exch *next;

        spin_lock_bh(&pool->lock);
restart:
        list_for_each_entry_safe(ep, next, &pool->ex_list, ex_list) {
                if ((lport == ep->lp) &&
                    (sid == 0 || sid == ep->sid) &&
                    (did == 0 || did == ep->did)) {
                        fc_exch_hold(ep);
                        spin_unlock_bh(&pool->lock);

                        fc_exch_reset(ep);

                        fc_exch_release(ep);
                        spin_lock_bh(&pool->lock);

                        /*
                         * must restart loop incase while lock
                         * was down multiple eps were released.
                         */
                        goto restart;
                }
        }
        pool->next_index = 0;
        pool->left = FC_XID_UNKNOWN;
        pool->right = FC_XID_UNKNOWN;
        spin_unlock_bh(&pool->lock);
}

/**
 * fc_exch_mgr_reset() - Reset all EMs of a local port
 * @lport: The local port whose EMs are to be reset
 * @sid:   The source ID
 * @did:   The destination ID
 *
 * Reset all EMs associated with a given local port. Release all
 * sequences and exchanges. If sid is non-zero then reset only the
 * exchanges sent from the local port's FID. If did is non-zero then
 * reset only exchanges destined for the local port's FID.
 */
void fc_exch_mgr_reset(struct fc_lport *lport, u32 sid, u32 did)
{
        struct fc_exch_mgr_anchor *ema;
        unsigned int cpu;

        list_for_each_entry(ema, &lport->ema_list, ema_list) {
                for_each_possible_cpu(cpu)
                        fc_exch_pool_reset(lport,
                                           per_cpu_ptr(ema->mp->pool, cpu),
                                           sid, did);
        }
}
EXPORT_SYMBOL(fc_exch_mgr_reset);

/**
 * fc_exch_lookup() - find an exchange
 * @lport: The local port
 * @xid: The exchange ID
 *
 * Returns exchange pointer with hold for caller, or NULL if not found.
 */
static struct fc_exch *fc_exch_lookup(struct fc_lport *lport, u32 xid)
{
        struct fc_exch_mgr_anchor *ema;

        list_for_each_entry(ema, &lport->ema_list, ema_list)
                if (ema->mp->min_xid <= xid && xid <= ema->mp->max_xid)
                        return fc_exch_find(ema->mp, xid);
        return NULL;
}

/**
 * fc_exch_els_rec() - Handler for ELS REC (Read Exchange Concise) requests
 * @rfp: The REC frame, not freed here.
 *
 * Note that the requesting port may be different than the S_ID in the request.
 */
static void fc_exch_els_rec(struct fc_frame *rfp)
{
        struct fc_lport *lport;
        struct fc_frame *fp;
        struct fc_exch *ep;
        struct fc_els_rec *rp;
        struct fc_els_rec_acc *acc;
        enum fc_els_rjt_reason reason = ELS_RJT_LOGIC;
        enum fc_els_rjt_explan explan;
        u32 sid;
        u16 rxid;
        u16 oxid;

        lport = fr_dev(rfp);
        rp = fc_frame_payload_get(rfp, sizeof(*rp));
        explan = ELS_EXPL_INV_LEN;
        if (!rp)
                goto reject;
        sid = ntoh24(rp->rec_s_id);
        rxid = ntohs(rp->rec_rx_id);
        oxid = ntohs(rp->rec_ox_id);

        ep = fc_exch_lookup(lport,
                            sid == fc_host_port_id(lport->host) ? oxid : rxid);
        explan = ELS_EXPL_OXID_RXID;
        if (!ep)
                goto reject;
        if (ep->oid != sid || oxid != ep->oxid)
                goto rel;
        if (rxid != FC_XID_UNKNOWN && rxid != ep->rxid)
                goto rel;
        fp = fc_frame_alloc(lport, sizeof(*acc));
        if (!fp)
                goto out;

        acc = fc_frame_payload_get(fp, sizeof(*acc));
        memset(acc, 0, sizeof(*acc));
        acc->reca_cmd = ELS_LS_ACC;
        acc->reca_ox_id = rp->rec_ox_id;
        memcpy(acc->reca_ofid, rp->rec_s_id, 3);
        acc->reca_rx_id = htons(ep->rxid);
        if (ep->sid == ep->oid)
                hton24(acc->reca_rfid, ep->did);
        else
                hton24(acc->reca_rfid, ep->sid);
        acc->reca_fc4value = htonl(ep->seq.rec_data);
        acc->reca_e_stat = htonl(ep->esb_stat & (ESB_ST_RESP |
                                                 ESB_ST_SEQ_INIT |
                                                 ESB_ST_COMPLETE));
        fc_fill_reply_hdr(fp, rfp, FC_RCTL_ELS_REP, 0);
        lport->tt.frame_send(lport, fp);
out:
        fc_exch_release(ep);
        return;

rel:
        fc_exch_release(ep);
reject:
        fc_seq_ls_rjt(rfp, reason, explan);
}

/**
 * fc_exch_rrq_resp() - Handler for RRQ responses
 * @sp:  The sequence that the RRQ is on
 * @fp:  The RRQ frame
 * @arg: The exchange that the RRQ is on
 *
 * TODO: fix error handler.
 */
static void fc_exch_rrq_resp(struct fc_seq *sp, struct fc_frame *fp, void *arg)
{
        struct fc_exch *aborted_ep = arg;
        unsigned int op;

        if (IS_ERR(fp)) {
                int err = PTR_ERR(fp);

                if (err == -FC_EX_CLOSED || err == -FC_EX_TIMEOUT)
                        goto cleanup;
                FC_EXCH_DBG(aborted_ep, "Cannot process RRQ, "
                            "frame error %d\n", err);
                return;
        }

        op = fc_frame_payload_op(fp);
        fc_frame_free(fp);

        switch (op) {
        case ELS_LS_RJT:
                FC_EXCH_DBG(aborted_ep, "LS_RJT for RRQ\n");
                /* fall through */
        case ELS_LS_ACC:
                goto cleanup;
        default:
                FC_EXCH_DBG(aborted_ep, "unexpected response op %x for RRQ\n",
                            op);
                return;
        }

cleanup:
        fc_exch_done(&aborted_ep->seq);
        /* drop hold for rec qual */
        fc_exch_release(aborted_ep);
}


/**
 * fc_exch_seq_send() - Send a frame using a new exchange and sequence
 * @lport:      The local port to send the frame on
 * @fp:         The frame to be sent
 * @resp:       The response handler for this request
 * @destructor: The destructor for the exchange
 * @arg:        The argument to be passed to the response handler
 * @timer_msec: The timeout period for the exchange
 *
 * The frame pointer with some of the header's fields must be
 * filled before calling this routine, those fields are:
 *
 * - routing control
 * - FC port did
 * - FC port sid
 * - FC header type
 * - frame control
 * - parameter or relative offset
 */
static struct fc_seq *fc_exch_seq_send(struct fc_lport *lport,
                                       struct fc_frame *fp,
                                       void (*resp)(struct fc_seq *,
                                                    struct fc_frame *fp,
                                                    void *arg),
                                       void (*destructor)(struct fc_seq *,
                                                          void *),
                                       void *arg, u32 timer_msec)
{
        struct fc_exch *ep;
        struct fc_seq *sp = NULL;
        struct fc_frame_header *fh;
        struct fc_fcp_pkt *fsp = NULL;
        int rc = 1;

        ep = fc_exch_alloc(lport, fp);
        if (!ep) {
                fc_frame_free(fp);
                return NULL;
        }
        ep->esb_stat |= ESB_ST_SEQ_INIT;
        fh = fc_frame_header_get(fp);
        fc_exch_set_addr(ep, ntoh24(fh->fh_s_id), ntoh24(fh->fh_d_id));
        ep->resp = resp;
        ep->destructor = destructor;
        ep->arg = arg;
        ep->r_a_tov = FC_DEF_R_A_TOV;
        ep->lp = lport;
        sp = &ep->seq;

        ep->fh_type = fh->fh_type; /* save for possbile timeout handling */
        ep->f_ctl = ntoh24(fh->fh_f_ctl);
        fc_exch_setup_hdr(ep, fp, ep->f_ctl);
        sp->cnt++;

        if (ep->xid <= lport->lro_xid && fh->fh_r_ctl == FC_RCTL_DD_UNSOL_CMD) {
                fsp = fr_fsp(fp);
                fc_fcp_ddp_setup(fr_fsp(fp), ep->xid);
        }

        if (unlikely(lport->tt.frame_send(lport, fp)))
                goto err;

        if (timer_msec)
                fc_exch_timer_set_locked(ep, timer_msec);
        ep->f_ctl &= ~FC_FC_FIRST_SEQ;  /* not first seq */

        if (ep->f_ctl & FC_FC_SEQ_INIT)
                ep->esb_stat &= ~ESB_ST_SEQ_INIT;
        spin_unlock_bh(&ep->ex_lock);
        return sp;
err:
        if (fsp)
                fc_fcp_ddp_done(fsp);
        rc = fc_exch_done_locked(ep);
        spin_unlock_bh(&ep->ex_lock);
        if (!rc)
                fc_exch_delete(ep);
        return NULL;
}

/**
 * fc_exch_rrq() - Send an ELS RRQ (Reinstate Recovery Qualifier) command
 * @ep: The exchange to send the RRQ on
 *
 * This tells the remote port to stop blocking the use of
 * the exchange and the seq_cnt range.
 */
static void fc_exch_rrq(struct fc_exch *ep)
{
        struct fc_lport *lport;
        struct fc_els_rrq *rrq;
        struct fc_frame *fp;
        u32 did;

        lport = ep->lp;

        fp = fc_frame_alloc(lport, sizeof(*rrq));
        if (!fp)
                goto retry;

        rrq = fc_frame_payload_get(fp, sizeof(*rrq));
        memset(rrq, 0, sizeof(*rrq));
        rrq->rrq_cmd = ELS_RRQ;
        hton24(rrq->rrq_s_id, ep->sid);
        rrq->rrq_ox_id = htons(ep->oxid);
        rrq->rrq_rx_id = htons(ep->rxid);

        did = ep->did;
        if (ep->esb_stat & ESB_ST_RESP)
                did = ep->sid;

        fc_fill_fc_hdr(fp, FC_RCTL_ELS_REQ, did,
                       lport->port_id, FC_TYPE_ELS,
                       FC_FC_FIRST_SEQ | FC_FC_END_SEQ | FC_FC_SEQ_INIT, 0);

        if (fc_exch_seq_send(lport, fp, fc_exch_rrq_resp, NULL, ep,
                             lport->e_d_tov))
                return;

retry:
        spin_lock_bh(&ep->ex_lock);
        if (ep->state & (FC_EX_RST_CLEANUP | FC_EX_DONE)) {
                spin_unlock_bh(&ep->ex_lock);
                /* drop hold for rec qual */
                fc_exch_release(ep);
                return;
        }
        ep->esb_stat |= ESB_ST_REC_QUAL;
        fc_exch_timer_set_locked(ep, ep->r_a_tov);
        spin_unlock_bh(&ep->ex_lock);
}

/**
 * fc_exch_els_rrq() - Handler for ELS RRQ (Reset Recovery Qualifier) requests
 * @fp: The RRQ frame, not freed here.
 */
static void fc_exch_els_rrq(struct fc_frame *fp)
{
        struct fc_lport *lport;
        struct fc_exch *ep = NULL;      /* request or subject exchange */
        struct fc_els_rrq *rp;
        u32 sid;
        u16 xid;
        enum fc_els_rjt_explan explan;

        lport = fr_dev(fp);
        rp = fc_frame_payload_get(fp, sizeof(*rp));
        explan = ELS_EXPL_INV_LEN;
        if (!rp)
                goto reject;

        /*
         * lookup subject exchange.
         */
        sid = ntoh24(rp->rrq_s_id);             /* subject source */
        xid = fc_host_port_id(lport->host) == sid ?
                        ntohs(rp->rrq_ox_id) : ntohs(rp->rrq_rx_id);
        ep = fc_exch_lookup(lport, xid);
        explan = ELS_EXPL_OXID_RXID;
        if (!ep)
                goto reject;
        spin_lock_bh(&ep->ex_lock);
        if (ep->oxid != ntohs(rp->rrq_ox_id))
                goto unlock_reject;
        if (ep->rxid != ntohs(rp->rrq_rx_id) &&
            ep->rxid != FC_XID_UNKNOWN)
                goto unlock_reject;
        explan = ELS_EXPL_SID;
        if (ep->sid != sid)
                goto unlock_reject;

        /*
         * Clear Recovery Qualifier state, and cancel timer if complete.
         */
        if (ep->esb_stat & ESB_ST_REC_QUAL) {
                ep->esb_stat &= ~ESB_ST_REC_QUAL;
                atomic_dec(&ep->ex_refcnt);     /* drop hold for rec qual */
        }
        if (ep->esb_stat & ESB_ST_COMPLETE)
                fc_exch_timer_cancel(ep);

        spin_unlock_bh(&ep->ex_lock);

        /*
         * Send LS_ACC.
         */
        fc_seq_ls_acc(fp);
        goto out;

unlock_reject:
        spin_unlock_bh(&ep->ex_lock);
reject:
        fc_seq_ls_rjt(fp, ELS_RJT_LOGIC, explan);
out:
        if (ep)
                fc_exch_release(ep);    /* drop hold from fc_exch_find */
}

/**
 * fc_exch_update_stats() - update exches stats to lport
 * @lport: The local port to update exchange manager stats
 */
void fc_exch_update_stats(struct fc_lport *lport)
{
        struct fc_host_statistics *st;
        struct fc_exch_mgr_anchor *ema;
        struct fc_exch_mgr *mp;

        st = &lport->host_stats;

        list_for_each_entry(ema, &lport->ema_list, ema_list) {
                mp = ema->mp;
                st->fc_no_free_exch += atomic_read(&mp->stats.no_free_exch);
                st->fc_no_free_exch_xid +=
                                atomic_read(&mp->stats.no_free_exch_xid);
                st->fc_xid_not_found += atomic_read(&mp->stats.xid_not_found);
                st->fc_xid_busy += atomic_read(&mp->stats.xid_busy);
                st->fc_seq_not_found += atomic_read(&mp->stats.seq_not_found);
                st->fc_non_bls_resp += atomic_read(&mp->stats.non_bls_resp);
        }
}
EXPORT_SYMBOL(fc_exch_update_stats);

/**
 * fc_exch_mgr_add() - Add an exchange manager to a local port's list of EMs
 * @lport: The local port to add the exchange manager to
 * @mp:    The exchange manager to be added to the local port
 * @match: The match routine that indicates when this EM should be used
 */
struct fc_exch_mgr_anchor *fc_exch_mgr_add(struct fc_lport *lport,
                                           struct fc_exch_mgr *mp,
                                           bool (*match)(struct fc_frame *))
{
        struct fc_exch_mgr_anchor *ema;

        ema = kmalloc(sizeof(*ema), GFP_ATOMIC);
        if (!ema)
                return ema;

        ema->mp = mp;
        ema->match = match;
        /* add EM anchor to EM anchors list */
        list_add_tail(&ema->ema_list, &lport->ema_list);
        kref_get(&mp->kref);
        return ema;
}
EXPORT_SYMBOL(fc_exch_mgr_add);

/**
 * fc_exch_mgr_destroy() - Destroy an exchange manager
 * @kref: The reference to the EM to be destroyed
 */
static void fc_exch_mgr_destroy(struct kref *kref)
{
        struct fc_exch_mgr *mp = container_of(kref, struct fc_exch_mgr, kref);

        mempool_destroy(mp->ep_pool);
        free_percpu(mp->pool);
        kfree(mp);
}

/**
 * fc_exch_mgr_del() - Delete an EM from a local port's list
 * @ema: The exchange manager anchor identifying the EM to be deleted
 */
void fc_exch_mgr_del(struct fc_exch_mgr_anchor *ema)
{
        /* remove EM anchor from EM anchors list */
        list_del(&ema->ema_list);
        kref_put(&ema->mp->kref, fc_exch_mgr_destroy);
        kfree(ema);
}
EXPORT_SYMBOL(fc_exch_mgr_del);

/**
 * fc_exch_mgr_list_clone() - Share all exchange manager objects
 * @src: Source lport to clone exchange managers from
 * @dst: New lport that takes references to all the exchange managers
 */
int fc_exch_mgr_list_clone(struct fc_lport *src, struct fc_lport *dst)
{
        struct fc_exch_mgr_anchor *ema, *tmp;

        list_for_each_entry(ema, &src->ema_list, ema_list) {
                if (!fc_exch_mgr_add(dst, ema->mp, ema->match))
                        goto err;
        }
        return 0;
err:
        list_for_each_entry_safe(ema, tmp, &dst->ema_list, ema_list)
                fc_exch_mgr_del(ema);
        return -ENOMEM;
}
EXPORT_SYMBOL(fc_exch_mgr_list_clone);

/**
 * fc_exch_mgr_alloc() - Allocate an exchange manager
 * @lport:   The local port that the new EM will be associated with
 * @class:   The default FC class for new exchanges
 * @min_xid: The minimum XID for exchanges from the new EM
 * @max_xid: The maximum XID for exchanges from the new EM
 * @match:   The match routine for the new EM
 */
struct fc_exch_mgr *fc_exch_mgr_alloc(struct fc_lport *lport,
                                      enum fc_class class,
                                      u16 min_xid, u16 max_xid,
                                      bool (*match)(struct fc_frame *))
{
        struct fc_exch_mgr *mp;
        u16 pool_exch_range;
        size_t pool_size;
        unsigned int cpu;
        struct fc_exch_pool *pool;

        if (max_xid <= min_xid || max_xid == FC_XID_UNKNOWN ||
            (min_xid & fc_cpu_mask) != 0) {
                FC_LPORT_DBG(lport, "Invalid min_xid 0x:%x and max_xid 0x:%x\n",
                             min_xid, max_xid);
                return NULL;
        }

        /*
         * allocate memory for EM
         */
        mp = kzalloc(sizeof(struct fc_exch_mgr), GFP_ATOMIC);
        if (!mp)
                return NULL;

        mp->class = class;
        /* adjust em exch xid range for offload */
        mp->min_xid = min_xid;

       /* reduce range so per cpu pool fits into PCPU_MIN_UNIT_SIZE pool */
        pool_exch_range = (PCPU_MIN_UNIT_SIZE - sizeof(*pool)) /
                sizeof(struct fc_exch *);
        if ((max_xid - min_xid + 1) / (fc_cpu_mask + 1) > pool_exch_range) {
                mp->max_xid = pool_exch_range * (fc_cpu_mask + 1) +
                        min_xid - 1;
        } else {
                mp->max_xid = max_xid;
                pool_exch_range = (mp->max_xid - mp->min_xid + 1) /
                        (fc_cpu_mask + 1);
        }

        mp->ep_pool = mempool_create_slab_pool(2, fc_em_cachep);
        if (!mp->ep_pool)
                goto free_mp;

        /*
         * Setup per cpu exch pool with entire exchange id range equally
         * divided across all cpus. The exch pointers array memory is
         * allocated for exch range per pool.
         */
        mp->pool_max_index = pool_exch_range - 1;

        /*
         * Allocate and initialize per cpu exch pool
         */
        pool_size = sizeof(*pool) + pool_exch_range * sizeof(struct fc_exch *);
        mp->pool = __alloc_percpu(pool_size, __alignof__(struct fc_exch_pool));
        if (!mp->pool)
                goto free_mempool;
        for_each_possible_cpu(cpu) {
                pool = per_cpu_ptr(mp->pool, cpu);
                pool->next_index = 0;
                pool->left = FC_XID_UNKNOWN;
                pool->right = FC_XID_UNKNOWN;
                spin_lock_init(&pool->lock);
                INIT_LIST_HEAD(&pool->ex_list);
        }

        kref_init(&mp->kref);
        if (!fc_exch_mgr_add(lport, mp, match)) {
                free_percpu(mp->pool);
                goto free_mempool;
        }

        /*
         * Above kref_init() sets mp->kref to 1 and then
         * call to fc_exch_mgr_add incremented mp->kref again,
         * so adjust that extra increment.
         */
        kref_put(&mp->kref, fc_exch_mgr_destroy);
        return mp;

free_mempool:
        mempool_destroy(mp->ep_pool);
free_mp:
        kfree(mp);
        return NULL;
}
EXPORT_SYMBOL(fc_exch_mgr_alloc);

/**
 * fc_exch_mgr_free() - Free all exchange managers on a local port
 * @lport: The local port whose EMs are to be freed
 */
void fc_exch_mgr_free(struct fc_lport *lport)
{
        struct fc_exch_mgr_anchor *ema, *next;

        flush_workqueue(fc_exch_workqueue);
        list_for_each_entry_safe(ema, next, &lport->ema_list, ema_list)
                fc_exch_mgr_del(ema);
}
EXPORT_SYMBOL(fc_exch_mgr_free);

/**
 * fc_find_ema() - Lookup and return appropriate Exchange Manager Anchor depending
 * upon 'xid'.
 * @f_ctl: f_ctl
 * @lport: The local port the frame was received on
 * @fh: The received frame header
 */
static struct fc_exch_mgr_anchor *fc_find_ema(u32 f_ctl,
                                              struct fc_lport *lport,
                                              struct fc_frame_header *fh)
{
        struct fc_exch_mgr_anchor *ema;
        u16 xid;

        if (f_ctl & FC_FC_EX_CTX)
                xid = ntohs(fh->fh_ox_id);
        else {
                xid = ntohs(fh->fh_rx_id);
                if (xid == FC_XID_UNKNOWN)
                        return list_entry(lport->ema_list.prev,
                                          typeof(*ema), ema_list);
        }

        list_for_each_entry(ema, &lport->ema_list, ema_list) {
                if ((xid >= ema->mp->min_xid) &&
                    (xid <= ema->mp->max_xid))
                        return ema;
        }
        return NULL;
}
/**
 * fc_exch_recv() - Handler for received frames
 * @lport: The local port the frame was received on
 * @fp: The received frame
 */
void fc_exch_recv(struct fc_lport *lport, struct fc_frame *fp)
{
        struct fc_frame_header *fh = fc_frame_header_get(fp);
        struct fc_exch_mgr_anchor *ema;
        u32 f_ctl;

        /* lport lock ? */
        if (!lport || lport->state == LPORT_ST_DISABLED) {
                FC_LPORT_DBG(lport, "Receiving frames for an lport that "
                             "has not been initialized correctly\n");
                fc_frame_free(fp);
                return;
        }

        f_ctl = ntoh24(fh->fh_f_ctl);
        ema = fc_find_ema(f_ctl, lport, fh);
        if (!ema) {
                FC_LPORT_DBG(lport, "Unable to find Exchange Manager Anchor,"
                                    "fc_ctl <0x%x>, xid <0x%x>\n",
                                     f_ctl,
                                     (f_ctl & FC_FC_EX_CTX) ?
                                     ntohs(fh->fh_ox_id) :
                                     ntohs(fh->fh_rx_id));
                fc_frame_free(fp);
                return;
        }

        /*
         * If frame is marked invalid, just drop it.
         */
        switch (fr_eof(fp)) {
        case FC_EOF_T:
                if (f_ctl & FC_FC_END_SEQ)
                        skb_trim(fp_skb(fp), fr_len(fp) - FC_FC_FILL(f_ctl));
                /* fall through */
        case FC_EOF_N:
                if (fh->fh_type == FC_TYPE_BLS)
                        fc_exch_recv_bls(ema->mp, fp);
                else if ((f_ctl & (FC_FC_EX_CTX | FC_FC_SEQ_CTX)) ==
                         FC_FC_EX_CTX)
                        fc_exch_recv_seq_resp(ema->mp, fp);
                else if (f_ctl & FC_FC_SEQ_CTX)
                        fc_exch_recv_resp(ema->mp, fp);
                else    /* no EX_CTX and no SEQ_CTX */
                        fc_exch_recv_req(lport, ema->mp, fp);
                break;
        default:
                FC_LPORT_DBG(lport, "dropping invalid frame (eof %x)",
                             fr_eof(fp));
                fc_frame_free(fp);
        }
}
EXPORT_SYMBOL(fc_exch_recv);

/**
 * fc_exch_init() - Initialize the exchange layer for a local port
 * @lport: The local port to initialize the exchange layer for
 */
int fc_exch_init(struct fc_lport *lport)
{
        if (!lport->tt.seq_start_next)
                lport->tt.seq_start_next = fc_seq_start_next;

        if (!lport->tt.seq_set_resp)
                lport->tt.seq_set_resp = fc_seq_set_resp;

        if (!lport->tt.exch_seq_send)
                lport->tt.exch_seq_send = fc_exch_seq_send;

        if (!lport->tt.seq_send)
                lport->tt.seq_send = fc_seq_send;

        if (!lport->tt.seq_els_rsp_send)
                lport->tt.seq_els_rsp_send = fc_seq_els_rsp_send;

        if (!lport->tt.exch_done)
                lport->tt.exch_done = fc_exch_done;

        if (!lport->tt.exch_mgr_reset)
                lport->tt.exch_mgr_reset = fc_exch_mgr_reset;

        if (!lport->tt.seq_exch_abort)
                lport->tt.seq_exch_abort = fc_seq_exch_abort;

        if (!lport->tt.seq_assign)
                lport->tt.seq_assign = fc_seq_assign;

        if (!lport->tt.seq_release)
                lport->tt.seq_release = fc_seq_release;

        return 0;
}
EXPORT_SYMBOL(fc_exch_init);

/**
 * fc_setup_exch_mgr() - Setup an exchange manager
 */
int fc_setup_exch_mgr(void)
{
        fc_em_cachep = kmem_cache_create("libfc_em", sizeof(struct fc_exch),
                                         0, SLAB_HWCACHE_ALIGN, NULL);
        if (!fc_em_cachep)
                return -ENOMEM;

        /*
         * Initialize fc_cpu_mask and fc_cpu_order. The
         * fc_cpu_mask is set for nr_cpu_ids rounded up
         * to order of 2's * power and order is stored
         * in fc_cpu_order as this is later required in
         * mapping between an exch id and exch array index
         * in per cpu exch pool.
         *
         * This round up is required to align fc_cpu_mask
         * to exchange id's lower bits such that all incoming
         * frames of an exchange gets delivered to the same
         * cpu on which exchange originated by simple bitwise
         * AND operation between fc_cpu_mask and exchange id.
         */
        fc_cpu_order = ilog2(roundup_pow_of_two(nr_cpu_ids));
        fc_cpu_mask = (1 << fc_cpu_order) - 1;

        fc_exch_workqueue = create_singlethread_workqueue("fc_exch_workqueue");
        if (!fc_exch_workqueue)
                goto err;
        return 0;
err:
        kmem_cache_destroy(fc_em_cachep);
        return -ENOMEM;
}

/**
 * fc_destroy_exch_mgr() - Destroy an exchange manager
 */
void fc_destroy_exch_mgr(void)
{
        destroy_workqueue(fc_exch_workqueue);
        kmem_cache_destroy(fc_em_cachep);
}