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Implement generic freeze feature

PATCH In review Takashi Sato 2 participants 3 messages Oct 27, 2008 – Oct 28, 2008

Subsystems (3)
VFS Device mapper Landlock security module
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Share & tools
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Takashi Sato

author
#0 lore raw

PATCH 2/3 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 Error number: If the filesystem has already been unfrozen,
errno is set to EINVAL.

Signed-off-by Takashi Sato <[email protected]>
Signed-off-by Masayuki Hamaguchi <[email protected]>
---
 fs/block_dev.c              |    2 +
 fs/buffer.c                 |   74 ++++++++++++++++++++++++++++++++++++++------
 fs/ioctl.c                  |   46 +++++++++++++++++++++++++++
 include/linux/buffer_head.h |    2 -
 include/linux/fs.h          |    7 ++++
 5 files changed, 121 insertions(+), 10 deletions(-)

diff -uprN -X linux-2.6.28-rc2-lockfs/Documentation/dontdiff linux-2.6.28-rc2-lockfs/fs/block_dev.c linux-2.6.28-rc2-fre eze/fs/block_dev.c

fs/block_dev.c +2 -0
@@ -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-2.6.28-rc2-lockfs/Documentation/dontdiff linux-2.6.28-rc2-lockfs/fs/buffer.c linux-2.6.28-rc2-freeze /fs/buffer.c

fs/buffer.c +65 -9

106 lines not on this page · raw message

diff -uprN -X linux-2.6.28-rc2-lockfs/Documentation/dontdiff linux-2.6.28-rc2-lockfs/fs/ioctl.c linux-2.6.28-rc2-freeze/ fs/ioctl.c

fs/ioctl.c +46 -0

58 lines not on this page · raw message

diff -uprN -X linux-2.6.28-rc2-lockfs/Documentation/dontdiff linux-2.6.28-rc2-lockfs/include/linux/buffer_head.h linux-2 .6.28-rc2-freeze/include/linux/buffer_head.h

include/linux/buffer_head.h +1 -1
@@ -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-2.6.28-rc2-lockfs/Documentation/dontdiff linux-2.6.28-rc2-lockfs/include/linux/fs.h linux-2.6.28-rc2 -freeze/include/linux/fs.h

include/linux/fs.h +7 -0
@@ -234,6 +234,8 @@ 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)

@@ -584,6 +586,11 @@ 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;
 };
 
 /*
#1 lore raw

fs/buffer.c EXPORT_SYMBOL(freeze_bdev); · line 267

Quoted 9 lines · On Mon, 27 Oct 2008 21:58:54 +0900 Takashi Sato <[email protected]> wrote:
fs/buffer.c +7 -1
-void thaw_bdev(struct block_device *bdev, struct super_block *sb)
+int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 {
+	int error = 0;
+
+	mutex_lock(&bdev->bd_fsfreeze_mutex);
+	if (!bdev->bd_fsfreeze_count) {
+		mutex_unlock(&bdev->bd_fsfreeze_mutex);
+		return -EINVAL;

This would be a programming error, yes?

If so, a WARN_ON is more appropriate than a silent runtime error.

Quoted 1 line
(quoted diff) +1 -0
+	}
author
#2 lore raw

Hi,

Quoted 11 lines

fs/buffer.c EXPORT_SYMBOL(freeze_bdev); · line 267

Quoted 9 lines
fs/buffer.c +7 -1
-void thaw_bdev(struct block_device *bdev, struct super_block *sb)
+int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 {
+ int error = 0;
+
+ mutex_lock(&bdev->bd_fsfreeze_mutex);
+ if (!bdev->bd_fsfreeze_count) {
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ return -EINVAL;

This would be a programming error, yes?

This is not a kernel programming error but a user's. thaw_bdev() is called via the unfreeze ioctl. If a user calls the unfreeze ioctl for an unfrozen filesystem, this error will be returned. So a WARN_ON isn't needed.

Quoted 3 lines

If so, a WARN_ON is more appropriate than a silent runtime error.

Quoted 1 line

+ }

Cheers, Takashi