[PATCH 1/3] Implement generic freeze feature

Takashi Sato
2008-09-08T11:52:45Z

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

Signed-off-by: Takashi Sato <t-sato@yk.jp.nec.com>
Signed-off-by: Masayuki Hamaguchi <m-hamaguchi@ys.jp.nec.com>
---
fs/block_dev.c | 2 +
fs/buffer.c | 34 ++++++++++++++++++++++++++++++-
fs/ioctl.c | 47 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/buffer_head.h | 2 -
include/linux/fs.h | 7 ++++++
5 files changed, 90 insertions(+), 2 deletions(-)

diff -uprN -X linux-2.6.27-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/fs/block_dev.c linux-2.6.27-rc5-freeze/fs
/block_dev.c
--- linux-2.6.27-rc5.org/fs/block_dev.c 2008-08-29 07:52:02.000000000 +0900
+++ linux-2.6.27-rc5-freeze/fs/block_dev.c 2008-09-05 20:00:29.000000000 +0900
@@ -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-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/fs/buffer.c linux-2.6.27-rc5-freeze/fs/bu
ffer.c
--- linux-2.6.27-rc5.org/fs/buffer.c 2008-08-29 07:52:02.000000000 +0900
+++ linux-2.6.27-rc5-freeze/fs/buffer.c 2008-09-05 20:23:13.000000000 +0900
@@ -196,11 +196,25 @@ int fsync_bdev(struct block_device *bdev
* happen on bdev until thaw_bdev() is called.
* If a superblock is found on this device, we take the s_umount semaphore
* on it to make sure nobody unmounts until the snapshot creation is done.
+ * The reference counter (bd_fsfreeze_count) guarantees that only the last
+ * unfreeze process can unfreeze the frozen filesystem actually when multiple
+ * freeze requests arrive simultaneously. It counts up in freeze_bdev() and
+ * count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze
+ * actually.
*/
struct super_block *freeze_bdev(struct block_device *bdev)
{
struct super_block *sb;

+ mutex_lock(&bdev->bd_fsfreeze_mutex);
+ if (bdev->bd_fsfreeze_count > 0) {
+ bdev->bd_fsfreeze_count++;
+ sb = get_super(bdev);
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ return sb;
+ }
+ bdev->bd_fsfreeze_count++;
+
down(&bdev->bd_mount_sem);
sb = get_super(bdev);
if (sb && !(sb->s_flags & MS_RDONLY)) {
@@ -219,6 +233,8 @@ struct super_block *freeze_bdev(struct b
}

sync_blockdev(bdev);
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+
return sb; /* thaw_bdev releases s->s_umount and bd_mount_sem */
}
EXPORT_SYMBOL(freeze_bdev);
@@ -230,8 +246,22 @@ EXPORT_SYMBOL(freeze_bdev);
*
* Unlocks the filesystem and marks it writeable again after freeze_bdev().
*/
-void thaw_bdev(struct block_device *bdev, struct super_block *sb)
+int thaw_bdev(struct block_device *bdev, struct super_block *sb)
{
+ mutex_lock(&bdev->bd_fsfreeze_mutex);
+ if (!bdev->bd_fsfreeze_count) {
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ return 0;
+ }
+
+ bdev->bd_fsfreeze_count--;
+ if (bdev->bd_fsfreeze_count > 0) {
+ if (sb)
+ drop_super(sb);
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ return 0;
+ }
+
if (sb) {
BUG_ON(sb->s_bdev != bdev);

@@ -244,6 +274,8 @@ void thaw_bdev(struct block_device *bdev
}

up(&bdev->bd_mount_sem);
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ return 0;
}
EXPORT_SYMBOL(thaw_bdev);

diff -uprN -X linux-2.6.27-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/fs/ioctl.c linux-2.6.27-rc5-freeze/fs/ioc
tl.c
--- linux-2.6.27-rc5.org/fs/ioctl.c 2008-08-29 07:52:02.000000000 +0900
+++ linux-2.6.27-rc5-freeze/fs/ioctl.c 2008-09-05 20:22:46.000000000 +0900
@@ -13,6 +13,7 @@
#include <linux/security.h>
#include <linux/module.h>
#include <linux/uaccess.h>
+#include <linux/buffer_head.h>

#include <asm/ioctls.h>

@@ -140,6 +141,43 @@ static int ioctl_fioasync(unsigned int f
return error;
}

+static int ioctl_freeze(struct file *filp)
+{
+ struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ /* If filesystem doesn't support freeze feature, return. */
+ if (sb->s_op->write_super_lockfs == NULL)
+ return -EOPNOTSUPP;
+
+ /* If a blockdevice-backed filesystem isn't specified, return. */
+ if (sb->s_bdev == NULL)
+ return -EINVAL;
+
+ /* Freeze */
+ sb = freeze_bdev(sb->s_bdev);
+ if (IS_ERR(sb))
+ return PTR_ERR(sb);
+ return 0;
+}
+
+static int ioctl_thaw(struct file *filp)
+{
+ struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ /* If a blockdevice-backed filesystem isn't specified, return EINVAL. */
+ if (sb->s_bdev == NULL)
+ return -EINVAL;
+
+ /* Thaw */
+ return thaw_bdev(sb->s_bdev, sb);
+}
+
/*
* When you add any new common ioctls to the switches above and below
* please update compat_sys_ioctl() too.
@@ -181,6 +219,15 @@ int do_vfs_ioctl(struct file *filp, unsi
} else
error = -ENOTTY;
break;
+
+ case FIFREEZE:
+ error = ioctl_freeze(filp);
+ break;
+
+ case FITHAW:
+ error = ioctl_thaw(filp);
+ break;
+
default:
if (S_ISREG(filp->f_path.dentry->d_inode->i_mode))
error = file_ioctl(filp, cmd, arg);
diff -uprN -X linux-2.6.27-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/include/linux/buffer_head.h linux-2.6.27-
rc5-freeze/include/linux/buffer_head.h
--- linux-2.6.27-rc5.org/include/linux/buffer_head.h 2008-08-29 07:52:02.000000000 +0900
+++ linux-2.6.27-rc5-freeze/include/linux/buffer_head.h 2008-09-05 20:16:12.000000000 +0900
@@ -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-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/include/linux/fs.h linux-2.6.27-rc5-freez
e/include/linux/fs.h
--- linux-2.6.27-rc5.org/include/linux/fs.h 2008-08-29 07:52:02.000000000 +0900
+++ linux-2.6.27-rc5-freeze/include/linux/fs.h 2008-09-05 20:18:21.000000000 +0900
@@ -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;
};

/*