fs/xfs/linux-2.6/mrlock.h

   1 /*
   2  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
   3  * All Rights Reserved.
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it would be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write the Free Software Foundation,
  16  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  17  */
  18 #ifndef __XFS_SUPPORT_MRLOCK_H__
  19 #define __XFS_SUPPORT_MRLOCK_H__
  20
  21 #include <linux/rwsem.h>
  22
  23 enum { MR_NONE, MR_ACCESS, MR_UPDATE };
  24
  25 typedef struct {
  26         struct rw_semaphore     mr_lock;
  27         int                     mr_writer;
  28 } mrlock_t;
  29
  30 #define mrinit(mrp, name)       \
  31         ( (mrp)->mr_writer = 0, init_rwsem(&(mrp)->mr_lock) )
  32 #define mrlock_init(mrp, t,n,s) mrinit(mrp, n)
  33 #define mrfree(mrp)             do { } while (0)
  34 #define mraccess(mrp)           mraccessf(mrp, 0)
  35 #define mrupdate(mrp)           mrupdatef(mrp, 0)
  36
  37 static inline void mraccessf(mrlock_t *mrp, int flags)
  38 {
  39         down_read(&mrp->mr_lock);
  40 }
  41
  42 static inline void mrupdatef(mrlock_t *mrp, int flags)
  43 {
  44         down_write(&mrp->mr_lock);
  45         mrp->mr_writer = 1;
  46 }
  47
  48 static inline int mrtryaccess(mrlock_t *mrp)
  49 {
  50         return down_read_trylock(&mrp->mr_lock);
  51 }
  52
  53 static inline int mrtryupdate(mrlock_t *mrp)
  54 {
  55         if (!down_write_trylock(&mrp->mr_lock))
  56                 return 0;
  57         mrp->mr_writer = 1;
  58         return 1;
  59 }
  60
  61 static inline void mrunlock(mrlock_t *mrp)
  62 {
  63         if (mrp->mr_writer) {
  64                 mrp->mr_writer = 0;
  65                 up_write(&mrp->mr_lock);
  66         } else {
  67                 up_read(&mrp->mr_lock);
  68         }
  69 }
  70
  71 static inline void mrdemote(mrlock_t *mrp)
  72 {
  73         mrp->mr_writer = 0;
  74         downgrade_write(&mrp->mr_lock);
  75 }
  76
  77 #ifdef DEBUG
  78 /*
  79  * Debug-only routine, without some platform-specific asm code, we can
  80  * now only answer requests regarding whether we hold the lock for write
  81  * (reader state is outside our visibility, we only track writer state).
  82  * Note: means !ismrlocked would give false positivies, so don't do that.
  83  */
  84 static inline int ismrlocked(mrlock_t *mrp, int type)
  85 {
  86         if (mrp && type == MR_UPDATE)
  87                 return mrp->mr_writer;
  88         return 1;
  89 }
  90 #endif
  91
  92 #endif /* __XFS_SUPPORT_MRLOCK_H__ */