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 <[email protected]>
Signed-off-by: Masayuki Hamaguchi <[email protected]>
---
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.org/fs/block_dev.c linux-2.6.25-freeze/fs/block_dev.c
--- linux-2.6.25.org/fs/block_dev.c 2008-04-17 11:49:44.000000000 +0900
+++ linux-2.6.25-freeze/fs/block_dev.c 2008-04-24 20:43:28.000000000 +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.org/fs/buffer.c linux-2.6.25-freeze/fs/buffer.c
--- linux-2.6.25.org/fs/buffer.c 2008-04-17 11:49:44.000000000 +0900
+++ linux-2.6.25-freeze/fs/buffer.c 2008-04-24 20:43:28.000000000 +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.org/fs/ioctl.c linux-2.6.25-freeze/fs/ioctl.c
--- linux-2.6.25.org/fs/ioctl.c 2008-04-17 11:49:44.000000000 +0900
+++ linux-2.6.25-freeze/fs/ioctl.c 2008-04-24 20:43:28.000000000 +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.org/fs/super.c linux-2.6.25-freeze/fs/super.c
--- linux-2.6.25.org/fs/super.c 2008-04-17 11:49:44.000000000 +0900
+++ linux-2.6.25-freeze/fs/super.c 2008-04-24 20:43:28.000000000 +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.org/include/linux/fs.h linux-2.6.25-freeze/include/linux
/fs.h
--- linux-2.6.25.org/include/linux/fs.h 2008-04-17 11:49:44.000000000 +0900
+++ linux-2.6.25-freeze/include/linux/fs.h 2008-04-24 20:43:28.000000000 +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);
On Mon, Apr 28, 2008 at 07:31:23PM +0900, Takashi Sato wrote:
> + /* Initialize semaphore for freeze. */
> + sema_init(&bdev->bd_freeze_sem, 1);
The freezing process is already protected by bd_mount_sem, so I don't
think there's need for another one.
> --- linux-2.6.25.org/fs/buffer.c 2008-04-17 11:49:44.000000000 +0900
> +++ linux-2.6.25-freeze/fs/buffer.c 2008-04-24 20:43:28.000000000 +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);
I think the protection against double freezes would be better done by
using a trylock on bd_mount_sem. In fact after that it could be changed
from a semaphore to a simple test_and_set_bit.
> error = -ENOTTY;
> break;
> +
> + case FIFREEZE: {
This would be better to split intot a small helper ala ioctl_fibmap()
> + case FITHAW: {
Same here.
Hi,
> On Mon, Apr 28, 2008 at 07:31:23PM +0900, Takashi Sato wrote:
>> + /* Initialize semaphore for freeze. */
>> + sema_init(&bdev->bd_freeze_sem, 1);
>
> The freezing process is already protected by bd_mount_sem, so I don't
> think there's need for another one.
>
[...]
>> down(&bdev->bd_mount_sem);
>> sb = get_super(bdev);
>
> I think the protection against double freezes would be better done by
> using a trylock on bd_mount_sem.
bd_mount_sem can protect against only freezes and cannot protect against
unfreezes. If multiple unfreezes run in parallel, the multiple up() for
bd_mount_sem might occur incorrectly.
> In fact after that it could be changed
> from a semaphore to a simple test_and_set_bit.
I will consider using test_and_set_bit.
>> error = -ENOTTY;
>> break;
>> +
>> + case FIFREEZE: {
>
> This would be better to split intot a small helper ala ioctl_fibmap()
>
>> + case FITHAW: {
>
> Same here.
OK. I will split small helper functions.
Cheers, Takashi
On Mon, Apr 28, 2008 at 09:59:55PM +0900, Takashi Sato wrote:
>> I think the protection against double freezes would be better done by
>> using a trylock on bd_mount_sem.
>
> bd_mount_sem can protect against only freezes and cannot protect against
> unfreezes. If multiple unfreezes run in parallel, the multiple up() for
> bd_mount_sem might occur incorrectly.
Indeed. The bit flag would fix that because unfreeze could then check
for the bit beeing set first. So that's probably the easiest way to go.
Hi,
>> bd_mount_sem can protect against only freezes and cannot protect against
>> unfreezes. If multiple unfreezes run in parallel, the multiple up() for
>> bd_mount_sem might occur incorrectly.
>
> Indeed. The bit flag would fix that because unfreeze could then check
> for the bit beeing set first. So that's probably the easiest way to go.
I think the bit flag is more efficient than the semaphore.
So I will consider whether it can be used for the freeze feature.
Cheers, Takashi