When multiple freeze requests arrive simultaneously, only the last
unfreeze process should unfreeze the frozen filesystem actually
(as Dave Chinner, Eric Sandeen and Alasdair G Kergon commented).
So I've added the reference counter to the freeze feature.
It counts up in freeze_bdev() and counts down in thaw_bdev().
When it becomes "0", thaw_bdev() will unfreeze actually.
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@xxxxxxxxxxxxx>
Signed-off-by: Masayuki Hamaguchi <m-hamaguchi@xxxxxxxxxxxxx>
---
fs/block_dev.c | 2 +
fs/buffer.c | 27 ++++++++++++++++++-
fs/ioctl.c | 61 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/buffer_head.h | 2 -
include/linux/fs.h | 6 ++++
5 files changed, 96 insertions(+), 2 deletions(-)
diff -uprN -X linux-2.6.26.org/Documentation/dontdiff linux-2.6.26.org/fs/block_dev.c linux-2.6.26-freeze/fs/block_dev.c
--- linux-2.6.26.org/fs/block_dev.c 2008-07-14 06:51:29.000000000 +0900
+++ linux-2.6.26-freeze/fs/block_dev.c 2008-07-18 15:38:03.000000000 +0900
@@ -285,6 +285,8 @@ static void init_once(struct kmem_cache
INIT_LIST_HEAD(&bdev->bd_holder_list);
#endif
inode_init_once(&ei->vfs_inode);
+ /* Initialize semaphore for freeze. */
+ sema_init(&bdev->bd_freeze_sem, 1);
}
static inline void __bd_forget(struct inode *inode)
diff -uprN -X linux-2.6.26.org/Documentation/dontdiff linux-2.6.26.org/fs/buffer.c linux-2.6.26-freeze/fs/buffer.c
--- linux-2.6.26.org/fs/buffer.c 2008-07-14 06:51:29.000000000 +0900
+++ linux-2.6.26-freeze/fs/buffer.c 2008-07-18 15:45:17.000000000 +0900
@@ -201,6 +201,15 @@ struct super_block *freeze_bdev(struct b
{
struct super_block *sb;
+ down(&bdev->bd_freeze_sem);
+ bdev->bd_freeze_count++;
+ if (bdev->bd_freeze_count > 1) {
+ sb = get_super(bdev);
+ drop_super(sb);
+ up(&bdev->bd_freeze_sem);
+ return sb;
+ }
+
down(&bdev->bd_mount_sem);
sb = get_super(bdev);
if (sb && !(sb->s_flags & MS_RDONLY)) {
@@ -219,6 +228,8 @@ struct super_block *freeze_bdev(struct b
}
sync_blockdev(bdev);
+ up(&bdev->bd_freeze_sem);
+
return sb; /* thaw_bdev releases s->s_umount and bd_mount_sem */
}
EXPORT_SYMBOL(freeze_bdev);
@@ -230,8 +241,20 @@ 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)
{
+
+ down(&bdev->bd_freeze_sem);
+ if (!bdev->bd_freeze_count) {
+ up(&bdev->bd_freeze_sem);
+ return 0;
+ }
+ bdev->bd_freeze_count--;
+ if (bdev->bd_freeze_count > 0) {
+ up(&bdev->bd_freeze_sem);
+ return 0;
+ }
+
if (sb) {
BUG_ON(sb->s_bdev != bdev);
@@ -244,6 +267,8 @@ void thaw_bdev(struct block_device *bdev
}
up(&bdev->bd_mount_sem);
+ up(&bdev->bd_freeze_sem);
+ return 0;
}
EXPORT_SYMBOL(thaw_bdev);
diff -uprN -X linux-2.6.26.org/Documentation/dontdiff linux-2.6.26.org/fs/ioctl.c linux-2.6.26-freeze/fs/ioctl.c
--- linux-2.6.26.org/fs/ioctl.c 2008-07-14 06:51:29.000000000 +0900
+++ linux-2.6.26-freeze/fs/ioctl.c 2008-07-18 21:24:42.000000000 +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>
@@ -141,6 +142,57 @@ static int ioctl_fioasync(unsigned int f
}
/*
+ * ioctl_freeze - Freeze the filesystem.
+ *
+ * @filp: target file
+ *
+ * Call freeze_bdev() to freeze the filesystem.
+ */
+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 regular file or a directory 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;
+}
+
+/*
+ * ioctl_thaw - Thaw the filesystem.
+ *
+ * @filp: target file
+ *
+ * Call thaw_bdev() to thaw the filesystem.
+ */
+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 regular file or a directory 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 +233,15 @@ 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-2.6.26.org/Documentation/dontdiff linux-2.6.26.org/include/linux/buffer_head.h linux-2.6.26-freeze/i
nclude/linux/buffer_head.h
--- linux-2.6.26.org/include/linux/buffer_head.h 2008-07-14 06:51:29.000000000 +0900
+++ linux-2.6.26-freeze/include/linux/buffer_head.h 2008-07-17 11:32:37.000000000 +0900
@@ -171,7 +171,7 @@ 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-2.6.26.org/Documentation/dontdiff linux-2.6.26.org/include/linux/fs.h linux-2.6.26-freeze/include/li
nux/fs.h
--- linux-2.6.26.org/include/linux/fs.h 2008-07-14 06:51:29.000000000 +0900
+++ linux-2.6.26-freeze/include/linux/fs.h 2008-07-18 15:34:46.000000000 +0900
@@ -224,6 +224,8 @@ 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)
@@ -548,6 +550,10 @@ struct block_device {
* care to not mess up bd_private for that case.
*/
unsigned long bd_private;
+ /* The counter of freeze processes */
+ int bd_freeze_count;
+ /* Semaphore for freeze */
+ struct semaphore bd_freeze_sem;
};
/*
--
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