fs/xfs/linux-2.6/mrlock.h

   1 /*
   2  * Copyright (c) 2000-2006 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         do { (mrp)->mr_writer = 0; init_rwsem(&(mrp)->mr_lock); } while (0)
  32 #define mrlock_init(mrp, t,n,s) mrinit(mrp, n)
  33 #define mrfree(mrp)             do { } while (0)
  34
  35 static inline void mraccess(mrlock_t *mrp)
  36 {
  37         down_read(&mrp->mr_lock);
  38 }
  39
  40 static inline void mrupdate(mrlock_t *mrp)
  41 {
  42         down_write(&mrp->mr_lock);
  43         mrp->mr_writer = 1;
  44 }
  45
  46 static inline int mrtryaccess(mrlock_t *mrp)
  47 {
  48         return down_read_trylock(&mrp->mr_lock);
  49 }
  50
  51 static inline int mrtryupdate(mrlock_t *mrp)
  52 {
  53         if (!down_write_trylock(&mrp->mr_lock))
  54                 return 0;
  55         mrp->mr_writer = 1;
  56         return 1;
  57 }
  58
  59 static inline void mrunlock(mrlock_t *mrp)
  60 {
  61         if (mrp->mr_writer) {
  62                 mrp->mr_writer = 0;
  63                 up_write(&mrp->mr_lock);
  64         } else {
  65                 up_read(&mrp->mr_lock);
  66         }
  67 }
  68
  69 static inline void mrdemote(mrlock_t *mrp)
  70 {
  71         mrp->mr_writer = 0;
  72         downgrade_write(&mrp->mr_lock);
  73 }
  74
  75 #ifdef DEBUG
  76 /*
  77  * Debug-only routine, without some platform-specific asm code, we can
  78  * now only answer requests regarding whether we hold the lock for write
  79  * (reader state is outside our visibility, we only track writer state).
  80  * Note: means !ismrlocked would give false positives, so don't do that.
  81  */
  82 static inline int ismrlocked(mrlock_t *mrp, int type)
  83 {
  84         if (mrp && type == MR_UPDATE)
  85                 return mrp->mr_writer;
  86         return 1;
  87 }
  88 #endif
  89
  90 #endif /* __XFS_SUPPORT_MRLOCK_H__ */