vfs: document ->d_real()

[deliverable/linux.git] / include / linux / dcache.h

#ifndef __LINUX_DCACHE_H
#define __LINUX_DCACHE_H

#include <linux/atomic.h>
#include <linux/list.h>
#include <linux/rculist.h>
#include <linux/rculist_bl.h>
#include <linux/spinlock.h>
#include <linux/seqlock.h>
#include <linux/cache.h>
#include <linux/rcupdate.h>
#include <linux/lockref.h>
#include <linux/stringhash.h>

struct path;
struct vfsmount;

/*
 * linux/include/linux/dcache.h
 *
 * Dirent cache data structures
 *
 * (C) Copyright 1997 Thomas Schoebel-Theuer,
 * with heavy changes by Linus Torvalds
 */

#define IS_ROOT(x) ((x) == (x)->d_parent)

/* The hash is always the low bits of hash_len */
#ifdef __LITTLE_ENDIAN
 #define HASH_LEN_DECLARE u32 hash; u32 len
 #define bytemask_from_count(cnt)       (~(~0ul << (cnt)*8))
#else
 #define HASH_LEN_DECLARE u32 len; u32 hash
 #define bytemask_from_count(cnt)       (~(~0ul >> (cnt)*8))
#endif

/*
 * "quick string" -- eases parameter passing, but more importantly
 * saves "metadata" about the string (ie length and the hash).
 *
 * hash comes first so it snuggles against d_parent in the
 * dentry.
 */
struct qstr {
        union {
                struct {
                        HASH_LEN_DECLARE;
                };
                u64 hash_len;
        };
        const unsigned char *name;
};

#define QSTR_INIT(n,l) { { { .len = l } }, .name = n }

struct dentry_stat_t {
        long nr_dentry;
        long nr_unused;
        long age_limit;          /* age in seconds */
        long want_pages;         /* pages requested by system */
        long dummy[2];
};
extern struct dentry_stat_t dentry_stat;

/*
 * Try to keep struct dentry aligned on 64 byte cachelines (this will
 * give reasonable cacheline footprint with larger lines without the
 * large memory footprint increase).
 */
#ifdef CONFIG_64BIT
# define DNAME_INLINE_LEN 32 /* 192 bytes */
#else
# ifdef CONFIG_SMP
#  define DNAME_INLINE_LEN 36 /* 128 bytes */
# else
#  define DNAME_INLINE_LEN 40 /* 128 bytes */
# endif
#endif

#define d_lock  d_lockref.lock

struct dentry {
        /* RCU lookup touched fields */
        unsigned int d_flags;           /* protected by d_lock */
        seqcount_t d_seq;               /* per dentry seqlock */
        struct hlist_bl_node d_hash;    /* lookup hash list */
        struct dentry *d_parent;        /* parent directory */
        struct qstr d_name;
        struct inode *d_inode;          /* Where the name belongs to - NULL is
                                         * negative */
        unsigned char d_iname[DNAME_INLINE_LEN];        /* small names */

        /* Ref lookup also touches following */
        struct lockref d_lockref;       /* per-dentry lock and refcount */
        const struct dentry_operations *d_op;
        struct super_block *d_sb;       /* The root of the dentry tree */
        unsigned long d_time;           /* used by d_revalidate */
        void *d_fsdata;                 /* fs-specific data */

        union {
                struct list_head d_lru;         /* LRU list */
                wait_queue_head_t *d_wait;      /* in-lookup ones only */
        };
        struct list_head d_child;       /* child of parent list */
        struct list_head d_subdirs;     /* our children */
        /*
         * d_alias and d_rcu can share memory
         */
        union {
                struct hlist_node d_alias;      /* inode alias list */
                struct hlist_bl_node d_in_lookup_hash;  /* only for in-lookup ones */
                struct rcu_head d_rcu;
        } d_u;
};

/*
 * dentry->d_lock spinlock nesting subclasses:
 *
 * 0: normal
 * 1: nested
 */
enum dentry_d_lock_class
{
        DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
        DENTRY_D_LOCK_NESTED
};

struct dentry_operations {
        int (*d_revalidate)(struct dentry *, unsigned int);
        int (*d_weak_revalidate)(struct dentry *, unsigned int);
        int (*d_hash)(const struct dentry *, struct qstr *);
        int (*d_compare)(const struct dentry *, const struct dentry *,
                        unsigned int, const char *, const struct qstr *);
        int (*d_delete)(const struct dentry *);
        void (*d_release)(struct dentry *);
        void (*d_prune)(struct dentry *);
        void (*d_iput)(struct dentry *, struct inode *);
        char *(*d_dname)(struct dentry *, char *, int);
        struct vfsmount *(*d_automount)(struct path *);
        int (*d_manage)(struct dentry *, bool);
        struct dentry *(*d_real)(struct dentry *, const struct inode *,
                                 unsigned int);
} ____cacheline_aligned;

/*
 * Locking rules for dentry_operations callbacks are to be found in
 * Documentation/filesystems/Locking. Keep it updated!
 *
 * FUrther descriptions are found in Documentation/filesystems/vfs.txt.
 * Keep it updated too!
 */

/* d_flags entries */
#define DCACHE_OP_HASH                  0x00000001
#define DCACHE_OP_COMPARE               0x00000002
#define DCACHE_OP_REVALIDATE            0x00000004
#define DCACHE_OP_DELETE                0x00000008
#define DCACHE_OP_PRUNE                 0x00000010

#define DCACHE_DISCONNECTED             0x00000020
     /* This dentry is possibly not currently connected to the dcache tree, in
      * which case its parent will either be itself, or will have this flag as
      * well.  nfsd will not use a dentry with this bit set, but will first
      * endeavour to clear the bit either by discovering that it is connected,
      * or by performing lookup operations.   Any filesystem which supports
      * nfsd_operations MUST have a lookup function which, if it finds a
      * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
      * dentry into place and return that dentry rather than the passed one,
      * typically using d_splice_alias. */

#define DCACHE_REFERENCED               0x00000040 /* Recently used, don't discard. */
#define DCACHE_RCUACCESS                0x00000080 /* Entry has ever been RCU-visible */

#define DCACHE_CANT_MOUNT               0x00000100
#define DCACHE_GENOCIDE                 0x00000200
#define DCACHE_SHRINK_LIST              0x00000400

#define DCACHE_OP_WEAK_REVALIDATE       0x00000800

#define DCACHE_NFSFS_RENAMED            0x00001000
     /* this dentry has been "silly renamed" and has to be deleted on the last
      * dput() */
#define DCACHE_COOKIE                   0x00002000 /* For use by dcookie subsystem */
#define DCACHE_FSNOTIFY_PARENT_WATCHED  0x00004000
     /* Parent inode is watched by some fsnotify listener */

#define DCACHE_DENTRY_KILLED            0x00008000

#define DCACHE_MOUNTED                  0x00010000 /* is a mountpoint */
#define DCACHE_NEED_AUTOMOUNT           0x00020000 /* handle automount on this dir */
#define DCACHE_MANAGE_TRANSIT           0x00040000 /* manage transit from this dirent */
#define DCACHE_MANAGED_DENTRY \
        (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)

#define DCACHE_LRU_LIST                 0x00080000

#define DCACHE_ENTRY_TYPE               0x00700000
#define DCACHE_MISS_TYPE                0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
#define DCACHE_WHITEOUT_TYPE            0x00100000 /* Whiteout dentry (stop pathwalk) */
#define DCACHE_DIRECTORY_TYPE           0x00200000 /* Normal directory */
#define DCACHE_AUTODIR_TYPE             0x00300000 /* Lookupless directory (presumed automount) */
#define DCACHE_REGULAR_TYPE             0x00400000 /* Regular file type (or fallthru to such) */
#define DCACHE_SPECIAL_TYPE             0x00500000 /* Other file type (or fallthru to such) */
#define DCACHE_SYMLINK_TYPE             0x00600000 /* Symlink (or fallthru to such) */

#define DCACHE_MAY_FREE                 0x00800000
#define DCACHE_FALLTHRU                 0x01000000 /* Fall through to lower layer */
#define DCACHE_ENCRYPTED_WITH_KEY       0x02000000 /* dir is encrypted with a valid key */
#define DCACHE_OP_REAL                  0x04000000

#define DCACHE_PAR_LOOKUP               0x10000000 /* being looked up (with parent locked shared) */
#define DCACHE_DENTRY_CURSOR            0x20000000

extern seqlock_t rename_lock;

/*
 * These are the low-level FS interfaces to the dcache..
 */
extern void d_instantiate(struct dentry *, struct inode *);
extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
extern int d_instantiate_no_diralias(struct dentry *, struct inode *);
extern void __d_drop(struct dentry *dentry);
extern void d_drop(struct dentry *dentry);
extern void d_delete(struct dentry *);
extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);

/* allocate/de-allocate */
extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
                                        wait_queue_head_t *);
extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
extern struct dentry *d_find_any_alias(struct inode *inode);
extern struct dentry * d_obtain_alias(struct inode *);
extern struct dentry * d_obtain_root(struct inode *);
extern void shrink_dcache_sb(struct super_block *);
extern void shrink_dcache_parent(struct dentry *);
extern void shrink_dcache_for_umount(struct super_block *);
extern void d_invalidate(struct dentry *);

/* only used at mount-time */
extern struct dentry * d_make_root(struct inode *);

/* <clickety>-<click> the ramfs-type tree */
extern void d_genocide(struct dentry *);

extern void d_tmpfile(struct dentry *, struct inode *);

extern struct dentry *d_find_alias(struct inode *);
extern void d_prune_aliases(struct inode *);

/* test whether we have any submounts in a subdir tree */
extern int have_submounts(struct dentry *);

/*
 * This adds the entry to the hash queues.
 */
extern void d_rehash(struct dentry *);
 
extern void d_add(struct dentry *, struct inode *);

extern void dentry_update_name_case(struct dentry *, struct qstr *);

/* used for rename() and baskets */
extern void d_move(struct dentry *, struct dentry *);
extern void d_exchange(struct dentry *, struct dentry *);
extern struct dentry *d_ancestor(struct dentry *, struct dentry *);

/* appendix may either be NULL or be used for transname suffixes */
extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
                                const struct qstr *name, unsigned *seq);

static inline unsigned d_count(const struct dentry *dentry)
{
        return dentry->d_lockref.count;
}

/*
 * helper function for dentry_operations.d_dname() members
 */
extern __printf(4, 5)
char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
extern char *simple_dname(struct dentry *, char *, int);

extern char *__d_path(const struct path *, const struct path *, char *, int);
extern char *d_absolute_path(const struct path *, char *, int);
extern char *d_path(const struct path *, char *, int);
extern char *dentry_path_raw(struct dentry *, char *, int);
extern char *dentry_path(struct dentry *, char *, int);

/* Allocation counts.. */

/**
 *      dget, dget_dlock -      get a reference to a dentry
 *      @dentry: dentry to get a reference to
 *
 *      Given a dentry or %NULL pointer increment the reference count
 *      if appropriate and return the dentry. A dentry will not be 
 *      destroyed when it has references.
 */
static inline struct dentry *dget_dlock(struct dentry *dentry)
{
        if (dentry)
                dentry->d_lockref.count++;
        return dentry;
}

static inline struct dentry *dget(struct dentry *dentry)
{
        if (dentry)
                lockref_get(&dentry->d_lockref);
        return dentry;
}

extern struct dentry *dget_parent(struct dentry *dentry);

/**
 *      d_unhashed -    is dentry hashed
 *      @dentry: entry to check
 *
 *      Returns true if the dentry passed is not currently hashed.
 */
 
static inline int d_unhashed(const struct dentry *dentry)
{
        return hlist_bl_unhashed(&dentry->d_hash);
}

static inline int d_unlinked(const struct dentry *dentry)
{
        return d_unhashed(dentry) && !IS_ROOT(dentry);
}

static inline int cant_mount(const struct dentry *dentry)
{
        return (dentry->d_flags & DCACHE_CANT_MOUNT);
}

static inline void dont_mount(struct dentry *dentry)
{
        spin_lock(&dentry->d_lock);
        dentry->d_flags |= DCACHE_CANT_MOUNT;
        spin_unlock(&dentry->d_lock);
}

extern void __d_lookup_done(struct dentry *);

static inline int d_in_lookup(struct dentry *dentry)
{
        return dentry->d_flags & DCACHE_PAR_LOOKUP;
}

static inline void d_lookup_done(struct dentry *dentry)
{
        if (unlikely(d_in_lookup(dentry))) {
                spin_lock(&dentry->d_lock);
                __d_lookup_done(dentry);
                spin_unlock(&dentry->d_lock);
        }
}

extern void dput(struct dentry *);

static inline bool d_managed(const struct dentry *dentry)
{
        return dentry->d_flags & DCACHE_MANAGED_DENTRY;
}

static inline bool d_mountpoint(const struct dentry *dentry)
{
        return dentry->d_flags & DCACHE_MOUNTED;
}

/*
 * Directory cache entry type accessor functions.
 */
static inline unsigned __d_entry_type(const struct dentry *dentry)
{
        return dentry->d_flags & DCACHE_ENTRY_TYPE;
}

static inline bool d_is_miss(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
}

static inline bool d_is_whiteout(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
}

static inline bool d_can_lookup(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
}

static inline bool d_is_autodir(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
}

static inline bool d_is_dir(const struct dentry *dentry)
{
        return d_can_lookup(dentry) || d_is_autodir(dentry);
}

static inline bool d_is_symlink(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
}

static inline bool d_is_reg(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
}

static inline bool d_is_special(const struct dentry *dentry)
{
        return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
}

static inline bool d_is_file(const struct dentry *dentry)
{
        return d_is_reg(dentry) || d_is_special(dentry);
}

static inline bool d_is_negative(const struct dentry *dentry)
{
        // TODO: check d_is_whiteout(dentry) also.
        return d_is_miss(dentry);
}

static inline bool d_is_positive(const struct dentry *dentry)
{
        return !d_is_negative(dentry);
}

/**
 * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
 * @dentry: The dentry in question
 *
 * Returns true if the dentry represents either an absent name or a name that
 * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
 * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
 * fallthrough marker in an opaque directory.
 *
 * Note!  (1) This should be used *only* by a filesystem to examine its own
 * dentries.  It should not be used to look at some other filesystem's
 * dentries.  (2) It should also be used in combination with d_inode() to get
 * the inode.  (3) The dentry may have something attached to ->d_lower and the
 * type field of the flags may be set to something other than miss or whiteout.
 */
static inline bool d_really_is_negative(const struct dentry *dentry)
{
        return dentry->d_inode == NULL;
}

/**
 * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
 * @dentry: The dentry in question
 *
 * Returns true if the dentry represents a name that maps to an inode
 * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
 * that is represented on medium as a 0,0 chardev.
 *
 * Note!  (1) This should be used *only* by a filesystem to examine its own
 * dentries.  It should not be used to look at some other filesystem's
 * dentries.  (2) It should also be used in combination with d_inode() to get
 * the inode.
 */
static inline bool d_really_is_positive(const struct dentry *dentry)
{
        return dentry->d_inode != NULL;
}

static inline int simple_positive(struct dentry *dentry)
{
        return d_really_is_positive(dentry) && !d_unhashed(dentry);
}

extern void d_set_fallthru(struct dentry *dentry);

static inline bool d_is_fallthru(const struct dentry *dentry)
{
        return dentry->d_flags & DCACHE_FALLTHRU;
}


extern int sysctl_vfs_cache_pressure;

static inline unsigned long vfs_pressure_ratio(unsigned long val)
{
        return mult_frac(val, sysctl_vfs_cache_pressure, 100);
}

/**
 * d_inode - Get the actual inode of this dentry
 * @dentry: The dentry to query
 *
 * This is the helper normal filesystems should use to get at their own inodes
 * in their own dentries and ignore the layering superimposed upon them.
 */
static inline struct inode *d_inode(const struct dentry *dentry)
{
        return dentry->d_inode;
}

/**
 * d_inode_rcu - Get the actual inode of this dentry with ACCESS_ONCE()
 * @dentry: The dentry to query
 *
 * This is the helper normal filesystems should use to get at their own inodes
 * in their own dentries and ignore the layering superimposed upon them.
 */
static inline struct inode *d_inode_rcu(const struct dentry *dentry)
{
        return ACCESS_ONCE(dentry->d_inode);
}

/**
 * d_backing_inode - Get upper or lower inode we should be using
 * @upper: The upper layer
 *
 * This is the helper that should be used to get at the inode that will be used
 * if this dentry were to be opened as a file.  The inode may be on the upper
 * dentry or it may be on a lower dentry pinned by the upper.
 *
 * Normal filesystems should not use this to access their own inodes.
 */
static inline struct inode *d_backing_inode(const struct dentry *upper)
{
        struct inode *inode = upper->d_inode;

        return inode;
}

/**
 * d_backing_dentry - Get upper or lower dentry we should be using
 * @upper: The upper layer
 *
 * This is the helper that should be used to get the dentry of the inode that
 * will be used if this dentry were opened as a file.  It may be the upper
 * dentry or it may be a lower dentry pinned by the upper.
 *
 * Normal filesystems should not use this to access their own dentries.
 */
static inline struct dentry *d_backing_dentry(struct dentry *upper)
{
        return upper;
}

/**
 * d_real - Return the real dentry
 * @dentry: the dentry to query
 * @inode: inode to select the dentry from multiple layers (can be NULL)
 * @flags: open flags to control copy-up behavior
 *
 * If dentry is on an union/overlay, then return the underlying, real dentry.
 * Otherwise return the dentry itself.
 *
 * See also: Documentation/filesystems/vfs.txt
 */
static inline struct dentry *d_real(struct dentry *dentry,
                                    const struct inode *inode,
                                    unsigned int flags)
{
        if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
                return dentry->d_op->d_real(dentry, inode, flags);
        else
                return dentry;
}

/**
 * d_real_inode - Return the real inode
 * @dentry: The dentry to query
 *
 * If dentry is on an union/overlay, then return the underlying, real inode.
 * Otherwise return d_inode().
 */
static inline struct inode *d_real_inode(struct dentry *dentry)
{
        return d_backing_inode(d_real(dentry, NULL, 0));
}


#endif  /* __LINUX_DCACHE_H */