[RFC PATCH 1/3] Implement generic freeze feature

Takashi Sato
2008-04-01T12:18:08Z

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 | 3 +++
fs/buffer.c | 25 +++++++++++++++++++++++++
fs/ioctl.c | 35 +++++++++++++++++++++++++++++++++++
fs/super.c | 32 +++++++++++++++++++++++++++++++-
include/linux/fs.h | 7 +++++++
5 files changed, 101 insertions(+), 1 deletion(-)

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc7.org/fs/block_dev.c linux-2.6.25-rc7-freeze/fs/block_
dev.c
--- linux-2.6.25-rc7.org/fs/block_dev.c 2008-03-26 10:38:14.000000000 +0900
+++ linux-2.6.25-rc7-freeze/fs/block_dev.c 2008-03-27 09:26:36.000000000 +0900
@@ -284,6 +284,9 @@ 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 /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc7.org/fs/buffer.c linux-2.6.25-rc7-freeze/fs/buffer.c
--- linux-2.6.25-rc7.org/fs/buffer.c 2008-03-26 10:38:14.000000000 +0900
+++ linux-2.6.25-rc7-freeze/fs/buffer.c 2008-03-26 20:32:23.000000000 +0900
@@ -201,6 +201,19 @@ struct super_block *freeze_bdev(struct b
{
struct super_block *sb;

+ down(&bdev->bd_freeze_sem);
+ sb = get_super_without_lock(bdev);
+
+ /* If super_block has been already frozen, return. */
+ if (sb && sb->s_frozen != SB_UNFROZEN) {
+ put_super(sb);
+ up(&bdev->bd_freeze_sem);
+ return sb;
+ }
+
+ if (sb)
+ put_super(sb);
+
down(&bdev->bd_mount_sem);
sb = get_super(bdev);
if (sb && !(sb->s_flags & MS_RDONLY)) {
@@ -219,6 +232,9 @@ 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);
@@ -232,6 +248,13 @@ EXPORT_SYMBOL(freeze_bdev);
*/
void thaw_bdev(struct block_device *bdev, struct super_block *sb)
{
+ down(&bdev->bd_freeze_sem);
+
+ if (sb && sb->s_frozen == SB_UNFROZEN) {
+ up(&bdev->bd_freeze_sem);
+ return;
+ }
+
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);
}
EXPORT_SYMBOL(thaw_bdev);

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc7.org/fs/ioctl.c linux-2.6.25-rc7-freeze/fs/ioctl.c
--- linux-2.6.25-rc7.org/fs/ioctl.c 2008-03-26 10:38:14.000000000 +0900
+++ linux-2.6.25-rc7-freeze/fs/ioctl.c 2008-03-26 20:22:17.000000000 +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>

@@ -181,6 +182,40 @@ int do_vfs_ioctl(struct file *filp, unsi
} else
error = -ENOTTY;
break;
+
+ case FIFREEZE: {
+ struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+
+ if (!capable(CAP_SYS_ADMIN)) {
+ error = -EPERM;
+ break;
+ }
+
+ /* If filesystem doesn't support freeze feature, return. */
+ if (sb->s_op->write_super_lockfs == NULL) {
+ error = -EINVAL;
+ break;
+ }
+
+ /* Freeze. */
+ freeze_bdev(sb->s_bdev);
+
+ break;
+ }
+
+ case FITHAW: {
+ struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+
+ if (!capable(CAP_SYS_ADMIN)) {
+ error = -EPERM;
+ break;
+ }
+
+ /* Thaw. */
+ thaw_bdev(sb->s_bdev, sb);
+ break;
+ }
+
default:
if (S_ISREG(filp->f_path.dentry->d_inode->i_mode))
error = file_ioctl(filp, cmd, arg);
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc7.org/fs/super.c linux-2.6.25-rc7-freeze/fs/super.c
--- linux-2.6.25-rc7.org/fs/super.c 2008-03-26 10:38:14.000000000 +0900
+++ linux-2.6.25-rc7-freeze/fs/super.c 2008-03-26 20:23:21.000000000 +0900
@@ -154,7 +154,7 @@ int __put_super_and_need_restart(struct
* Drops a temporary reference, frees superblock if there's no
* references left.
*/
-static void put_super(struct super_block *sb)
+void put_super(struct super_block *sb)
{
spin_lock(&sb_lock);
__put_super(sb);
@@ -507,6 +507,36 @@ rescan:

EXPORT_SYMBOL(get_super);

+/*
+ * get_super_without_lock - Get super_block from block_device without lock.
+ * @bdev: block device struct
+ *
+ * Scan the superblock list and finds the superblock of the file system
+ * mounted on the block device given. This doesn't lock anyone.
+ * %NULL is returned if no match is found.
+ */
+struct super_block *get_super_without_lock(struct block_device *bdev)
+{
+ struct super_block *sb;
+
+ if (!bdev)
+ return NULL;
+
+ spin_lock(&sb_lock);
+ list_for_each_entry(sb, &super_blocks, s_list) {
+ if (sb->s_bdev == bdev) {
+ if (sb->s_root) {
+ sb->s_count++;
+ spin_unlock(&sb_lock);
+ return sb;
+ }
+ }
+ }
+ spin_unlock(&sb_lock);
+ return NULL;
+}
+EXPORT_SYMBOL(get_super_without_lock);
+
struct super_block * user_get_super(dev_t dev)
{
struct super_block *sb;
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc7.org/include/linux/fs.h linux-2.6.25-rc7-freeze/inclu
de/linux/fs.h
--- linux-2.6.25-rc7.org/include/linux/fs.h 2008-03-26 10:38:14.000000000 +0900
+++ linux-2.6.25-rc7-freeze/include/linux/fs.h 2008-03-26 20:27:44.000000000 +0900
@@ -223,6 +223,8 @@ 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 +550,9 @@ struct block_device {
* care to not mess up bd_private for that case.
*/
unsigned long bd_private;
+
+ /* Semaphore for freeze */
+ struct semaphore bd_freeze_sem;
};

/*
@@ -1926,7 +1931,9 @@ extern int do_vfs_ioctl(struct file *fil
extern void get_filesystem(struct file_system_type *fs);
extern void put_filesystem(struct file_system_type *fs);
extern struct file_system_type *get_fs_type(const char *name);
+extern void put_super(struct super_block *sb);
extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_without_lock(struct block_device *);
extern struct super_block *user_get_super(dev_t);
extern void drop_super(struct super_block *sb);