Re: [RFC] ext3 freeze feature ver 0.2

[Takashi Sato <t-sato@yk.jp.nec.com>]

Hi,

Andreas Dilger wrote:
>> > o Elevate XFS ioctl numbers (XFS_IOC_FREEZE and XFS_IOC_THAW) to the VFS
>> >   As Andreas Dilger and Christoph Hellwig advised me, I have elevated
>> >   them to include/linux/fs.h as below.
>> >     #define FIFREEZE        _IOWR('X', 119, int)
>> > 　  #define FITHAW          _IOWR('X', 120, int)
>> >   The ioctl numbers used by XFS applications don't need to be changed.
>> >   But my following ioctl for the freeze needs the parameter
>> >   as the timeout period.  So if XFS applications don't want the timeout
>> >   feature as the current implementation, the parameter needs to be
>> >   changed 1 (level?) into 0.
>> 
>> So, existing xfs applications calling the xfs ioctl now will behave
>> differently, right?  We can only keep the same ioctl number if the
>> calling semantics are the same.  Keeping the same number but changing
>> the semantics is harmful, IMHO....
>
>Do we know what this parameter was supposed to mean?
>
>We could special case "1" if needed to keep compatibility (documenting
>this clearly), either making it == 0, or some very long timeout (1h
>or whatever).  A relatively minor wart I think.

I agree.

Because the original xfs_freeze doesn't have the timeout feature,
I think my freeze ioctl had better not do the timeout in case of
specifying 1 as ioctl's parameter.
So I have modified my freeze ioctl not to set the timeout in case of
specifying 1 or 0 as below. 
(I have attached the modified patch in this mail.)
  int ioctl(int fd, int FIFREEZE, long *timeval)
    fd: The file descriptor of the mountpoint
    FIFREEZE: The request code for the freeze
    timeval: The timeout value expressed in seconds
             If it's 0 or 1, the timeout isn't set.
    Return value: 0 if the operation succeeds. Otherwise, -1

I have tested my attached patch and confirmed that the original
xfs_freeze could freeze the filesystem without the timeout.

Any comments are very welcome.

I haven't changed the following ioctls from the previous version.
o Reset the timeout period
  int ioctl(int fd, int FIFREEZE_RESET_TIMEOUT, long *timeval)
    fd:file descriptor of mountpoint
    FIFREEZE_RESET_TIMEOUT:request code for reset of timeout period
    timeval:new timeout period
    Return value: 0 if the operation succeeds. Otherwise, -1
    Error number: If the filesystem has already been unfrozen,
                  it sets EINVAL to errno.

o Unfreeze the filesystem
  int ioctl(int fd, int FITHAW, long *timeval)
    fd: The file descriptor of the mountpoint
    FITHAW: request code for unfreeze
    timeval: Ignored
    Return value: 0 if the operation succeeds. Otherwise, -1

Cheers, Takashi

Signed-off-by: Takashi Sato <t-sato@yk.jp.nec.com>
---
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/drivers/md/dm.c linux-2.6.25-rc3-freeze/drivers/
md/dm.c
--- linux-2.6.25-rc3.org/drivers/md/dm.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/drivers/md/dm.c	2008-02-25 10:50:04.000000000 +0900
@@ -1407,7 +1407,7 @@ static int lock_fs(struct mapped_device 
 
 	WARN_ON(md->frozen_sb);
 
-	md->frozen_sb = freeze_bdev(md->suspended_bdev);
+	md->frozen_sb = freeze_bdev(md->suspended_bdev, 0);
 	if (IS_ERR(md->frozen_sb)) {
 		r = PTR_ERR(md->frozen_sb);
 		md->frozen_sb = NULL;
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/fs/block_dev.c linux-2.6.25-rc3-freeze/fs/block_
dev.c
--- linux-2.6.25-rc3.org/fs/block_dev.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/fs/block_dev.c	2008-02-25 10:50:04.000000000 +0900
@@ -284,6 +284,11 @@ 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);
+	/* Setup freeze timeout function. */
+	INIT_DELAYED_WORK(&bdev->bd_freeze_timeout, freeze_timeout);
 }
 
 static inline void __bd_forget(struct inode *inode)
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/fs/buffer.c linux-2.6.25-rc3-freeze/fs/buffer.c
--- linux-2.6.25-rc3.org/fs/buffer.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/fs/buffer.c	2008-02-25 10:50:04.000000000 +0900
@@ -190,17 +190,33 @@ int fsync_bdev(struct block_device *bdev
 
 /**
  * freeze_bdev  --  lock a filesystem and force it into a consistent state
- * @bdev:	blockdevice to lock
+ * @bdev:		blockdevice to lock
+ * @timeout_msec:	timeout period
  *
  * This takes the block device bd_mount_sem to make sure no new mounts
  * 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.
+ * If timeout_msec is bigger than 0, this registers the delayed work for
+ * timeout of the freeze feature.
  */
-struct super_block *freeze_bdev(struct block_device *bdev)
+struct super_block *freeze_bdev(struct block_device *bdev, long timeout_msec)
 {
 	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 +235,13 @@ struct super_block *freeze_bdev(struct b
 	}
 
 	sync_blockdev(bdev);
+
+	/* Setup unfreeze timer. */
+	if (timeout_msec > 0)
+		add_freeze_timeout(bdev, timeout_msec);
+
+	up(&bdev->bd_freeze_sem);
+
 	return sb;	/* thaw_bdev releases s->s_umount and bd_mount_sem */
 }
 EXPORT_SYMBOL(freeze_bdev);
@@ -232,6 +255,16 @@ 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;
+	}
+
+	/* Delete unfreeze timer. */
+	del_freeze_timeout(bdev);
+
 	if (sb) {
 		BUG_ON(sb->s_bdev != bdev);
 
@@ -244,6 +277,8 @@ 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-rc3.org/fs/ioctl.c linux-2.6.25-rc3-freeze/fs/ioctl.c
--- linux-2.6.25-rc3.org/fs/ioctl.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/fs/ioctl.c	2008-02-27 10:30:30.000000000 +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 +182,102 @@ int do_vfs_ioctl(struct file *filp, unsi
 		} else
 			error = -ENOTTY;
 		break;
+
+	case FIFREEZE: {
+		long timeout_sec;
+		long timeout_msec;
+		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;
+		}
+
+		/* arg(sec) to tick value. */
+		error = get_user(timeout_sec, (long __user *) arg);
+		if (error != 0)
+			break;
+		/* 
+		 * If 1 is specified as the timeout period,
+		 * it will be changed into 0 to keep the compatibility
+		 * of XFS application(xfs_freeze).
+		 */
+		if (timeout_sec < 0) {
+			error = -EINVAL;
+			break;
+		} else if (timeout_sec < 2) {
+			timeout_sec = 0;	
+		}
+
+		timeout_msec = timeout_sec * 1000;
+		/* overflow case */
+		if (timeout_msec < 0) {
+			error = -EINVAL;
+			break;
+		}
+
+		/* Freeze. */
+		freeze_bdev(sb->s_bdev, timeout_msec);
+
+		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;
+	}
+
+	case FIFREEZE_RESET_TIMEOUT: {
+		long timeout_sec;
+		long timeout_msec;
+		struct super_block *sb
+			= filp->f_path.dentry->d_inode->i_sb;
+
+		if (!capable(CAP_SYS_ADMIN)) {
+			error = -EPERM;
+			break;
+		}
+
+		/* arg(sec) to tick value */
+		error = get_user(timeout_sec, (long __user *) arg);
+		if (error)
+			break;
+		timeout_msec = timeout_sec * 1000;
+		if (timeout_msec < 0) {
+			error = -EINVAL;
+			break;
+		}
+
+		if (sb) {
+			down(&sb->s_bdev->bd_freeze_sem);
+			if (sb->s_frozen == SB_UNFROZEN) {
+				up(&sb->s_bdev->bd_freeze_sem);
+				error = -EINVAL;
+				break;
+			}
+			/* setup unfreeze timer */
+			if (timeout_msec > 0)
+				add_freeze_timeout(sb->s_bdev,
+					timeout_msec);
+			up(&sb->s_bdev->bd_freeze_sem);
+		}
+		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-rc3.org/fs/super.c linux-2.6.25-rc3-freeze/fs/super.c
--- linux-2.6.25-rc3.org/fs/super.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/fs/super.c	2008-02-25 10:50:04.000000000 +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;
@@ -952,3 +982,56 @@ struct vfsmount *kern_mount_data(struct 
 }
 
 EXPORT_SYMBOL_GPL(kern_mount_data);
+
+/*
+ * freeze_timeout - Thaw the filesystem.
+ *
+ * @work:	work queue (delayed_work.work)
+ *
+ * Called by the delayed work when elapsing the timeout period.
+ * Thaw the filesystem.
+ */
+void freeze_timeout(struct work_struct *work)
+{
+	struct block_device *bd = container_of(work,
+			struct block_device, bd_freeze_timeout.work);
+
+	struct super_block *sb = get_super_without_lock(bd);
+
+	BUG_ON(sb == NULL);
+
+	thaw_bdev(bd, sb);
+
+	put_super(sb);
+}
+EXPORT_SYMBOL_GPL(freeze_timeout);
+
+/*
+ * add_freeze_timeout - Add timeout for freeze.
+ *
+ * @bdev:		block device struct
+ * @timeout_msec:	timeout period
+ *
+ * Add the delayed work for freeze timeout to the delayed work queue.
+ */
+void add_freeze_timeout(struct block_device *bdev, long timeout_msec)
+{
+	s64 timeout_jiffies = msecs_to_jiffies(timeout_msec);
+
+	/* Set delayed work queue */
+	cancel_delayed_work(&bdev->bd_freeze_timeout);
+	schedule_delayed_work(&bdev->bd_freeze_timeout, timeout_jiffies);
+}
+
+/*
+ * del_freeze_timeout - Delete timeout for freeze.
+ *
+ * @bdev:	block device struct
+ *
+ * Delete the delayed work for freeze timeout from the delayed work queue.
+ */
+void del_freeze_timeout(struct block_device *bdev)
+{
+	if (delayed_work_pending(&bdev->bd_freeze_timeout))
+		cancel_delayed_work(&bdev->bd_freeze_timeout);
+}
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/fs/xfs/linux-2.6/xfs_ioctl.c linux-2.6.25-rc3-fr
eeze/fs/xfs/linux-2.6/xfs_ioctl.c
--- linux-2.6.25-rc3.org/fs/xfs/linux-2.6/xfs_ioctl.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/fs/xfs/linux-2.6/xfs_ioctl.c	2008-02-25 10:50:04.000000000 +0900
@@ -911,7 +911,7 @@ xfs_ioctl(
 			return -EPERM;
 
 		if (inode->i_sb->s_frozen == SB_UNFROZEN)
-			freeze_bdev(inode->i_sb->s_bdev);
+			freeze_bdev(inode->i_sb->s_bdev, 0);
 		return 0;
 
 	case XFS_IOC_THAW:
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/fs/xfs/xfs_fsops.c linux-2.6.25-rc3-freeze/fs/xf
s/xfs_fsops.c
--- linux-2.6.25-rc3.org/fs/xfs/xfs_fsops.c	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/fs/xfs/xfs_fsops.c	2008-02-25 10:50:04.000000000 +0900
@@ -623,7 +623,7 @@ xfs_fs_goingdown(
 {
 	switch (inflags) {
 	case XFS_FSOP_GOING_FLAGS_DEFAULT: {
-		struct super_block *sb = freeze_bdev(mp->m_super->s_bdev);
+		struct super_block *sb = freeze_bdev(mp->m_super->s_bdev, 0);
 
 		if (sb && !IS_ERR(sb)) {
 			xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT);
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/include/linux/buffer_head.h linux-2.6.25-rc3-fre
eze/include/linux/buffer_head.h
--- linux-2.6.25-rc3.org/include/linux/buffer_head.h	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/include/linux/buffer_head.h	2008-02-25 10:50:04.000000000 +0900
@@ -170,7 +170,7 @@ int sync_blockdev(struct block_device *b
 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 *);
+struct super_block *freeze_bdev(struct block_device *, long timeout_msec);
 void thaw_bdev(struct block_device *, struct super_block *);
 int fsync_super(struct super_block *);
 int fsync_no_super(struct block_device *);
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc3.org/include/linux/fs.h linux-2.6.25-rc3-freeze/inclu
de/linux/fs.h
--- linux-2.6.25-rc3.org/include/linux/fs.h	2008-02-25 06:25:54.000000000 +0900
+++ linux-2.6.25-rc3-freeze/include/linux/fs.h	2008-02-25 10:50:04.000000000 +0900
@@ -8,6 +8,7 @@
 
 #include <linux/limits.h>
 #include <linux/ioctl.h>
+#include <linux/workqueue.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -223,6 +224,9 @@ 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	FIFREEZE_RESET_TIMEOUT	_IO(0x00, 3)	/* Reset freeze timeout */
 
 #define	FS_IOC_GETFLAGS			_IOR('f', 1, long)
 #define	FS_IOC_SETFLAGS			_IOW('f', 2, long)
@@ -548,6 +552,11 @@ struct block_device {
 	 * care to not mess up bd_private for that case.
 	 */
 	unsigned long		bd_private;
+
+	/* Delayed work for freeze */
+	struct delayed_work	bd_freeze_timeout;
+	/* Semaphore for freeze */
+	struct semaphore	bd_freeze_sem;
 };
 
 /*
@@ -1926,7 +1935,9 @@ 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);
 
@@ -2070,7 +2081,6 @@ ssize_t simple_attr_read(struct file *fi
 ssize_t simple_attr_write(struct file *file, const char __user *buf,
 			  size_t len, loff_t *ppos);
 
-
 #ifdef CONFIG_SECURITY
 static inline char *alloc_secdata(void)
 {
@@ -2097,5 +2107,9 @@ int proc_nr_files(struct ctl_table *tabl
 
 int get_filesystem_list(char * buf);
 
+extern void add_freeze_timeout(struct block_device *bdev, long timeout_msec);
+extern void del_freeze_timeout(struct block_device *bdev);
+extern void freeze_timeout(struct work_struct *work);
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_FS_H */