Implement generic freeze feature

The ioctls for the generic freeze feature are below.
o Freeze the filesystem
int ioctl(int fd, int FIFREEZE, arg)
fd: The file descriptor of the mountpoint
FIFREEZE: request code for the freeze
arg: Ignored
Return value: 0 if the operation succeeds. Otherwise, -1

o Unfreeze the filesystem
int ioctl(int fd, int FITHAW, arg)
fd: The file descriptor of the mountpoint
FITHAW: request code for unfreeze
arg: Ignored
Return value: 0 if the operation succeeds. Otherwise, -1

---
 fs/block_dev.c              |    2 +
 fs/buffer.c                 |   74 ++++++++++++++++++++++++++++++++++++++------
 fs/ioctl.c                  |   47 +++++++++++++++++++++++++++
 include/linux/buffer_head.h |    2 -
 include/linux/fs.h          |    7 ++++
 5 files changed, 122 insertions(+), 10 deletions(-)

diff -uprN -X linux-2.6.27-rc7-lockfs-jfs/Documentation/dontdiff linux-2.6.27-rc7-lockfs-jfs/fs/block_dev.c linux-2.6.27 -rc7-freeze/fs/block_dev.c

@@ -285,6 +285,8 @@ static void init_once(void *foo)
 	INIT_LIST_HEAD(&bdev->bd_holder_list);
 #endif
 	inode_init_once(&ei->vfs_inode);
+	/* Initialize mutex for freeze. */
+	mutex_init(&bdev->bd_fsfreeze_mutex);
 }
 
 static inline void __bd_forget(struct inode *inode)

diff -uprN -X linux-2.6.27-rc7-lockfs-jfs/Documentation/dontdiff linux-2.6.27-rc7-lockfs-jfs/fs/buffer.c linux-2.6.27-rc 7-freeze/fs/buffer.c

diff -uprN -X linux-2.6.27-rc7-lockfs-jfs/Documentation/dontdiff linux-2.6.27-rc7-lockfs-jfs/fs/ioctl.c linux-2.6.27-rc7 -freeze/fs/ioctl.c

diff -uprN -X linux-2.6.27-rc7-lockfs-jfs/Documentation/dontdiff linux-2.6.27-rc7-lockfs-jfs/include/linux/buffer_head.h
linux-2.6.27-rc7-freeze/include/linux/buffer_head.h

@@ -170,7 +170,7 @@ void __wait_on_buffer(struct buffer_head
 wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
 int fsync_bdev(struct block_device *);
 struct super_block *freeze_bdev(struct block_device *);
-void thaw_bdev(struct block_device *, struct super_block *);
+int thaw_bdev(struct block_device *, struct super_block *);
 int fsync_super(struct super_block *);
 int fsync_no_super(struct block_device *);
 struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,

diff -uprN -X linux-2.6.27-rc7-lockfs-jfs/Documentation/dontdiff linux-2.6.27-rc7-lockfs-jfs/include/linux/fs.h linux-2. 6.27-rc7-freeze/include/linux/fs.h

@@ -226,6 +226,8 @@ extern int dir_notify_enable;
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */
 #define FIGETBSZ   _IO(0x00,2)	/* get the block size used for bmap */
+#define FIFREEZE	_IOWR('X', 119, int)	/* Freeze */
+#define FITHAW		_IOWR('X', 120, int)	/* Thaw */
 
 #define	FS_IOC_GETFLAGS			_IOR('f', 1, long)
 #define	FS_IOC_SETFLAGS			_IOW('f', 2, long)

@@ -574,6 +576,11 @@ struct block_device {
 	 * care to not mess up bd_private for that case.
 	 */
 	unsigned long		bd_private;
+
+	/* The counter of freeze processes */
+	int			bd_fsfreeze_count;
+	/* Mutex for freeze */
+	struct mutex		bd_fsfreeze_mutex;
 };
 
 /*