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[PATCH 1/3] Implement generic freeze feature

To: akpm@xxxxxxxxxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx
Subject: [PATCH 1/3] Implement generic freeze feature
From: Takashi Sato <t-sato@xxxxxxxxxxxxx>
Date: Mon, 30 Jun 2008 21:23:23 +0900
Cc: "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "dm-devel@xxxxxxxxxx" <dm-devel@xxxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx
Sender: xfs-bounce@xxxxxxxxxxx
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>
---
diff -uprN -X linux-2.6.26-rc7.org/Documentation/dontdiff 
linux-2.6.26-rc7.org/fs/buffer.c linux-2.6.26-rc7-freeze/fs/bu
ffer.c
--- linux-2.6.26-rc7.org/fs/buffer.c    2008-06-25 12:08:10.000000000 +0900
+++ linux-2.6.26-rc7-freeze/fs/buffer.c 2008-06-27 09:18:19.000000000 +0900
@@ -201,6 +201,21 @@ struct super_block *freeze_bdev(struct b
 {
        struct super_block *sb;
 
+       if (test_and_set_bit(BD_FREEZE_OP, &bdev->bd_state))
+               return ERR_PTR(-EBUSY);
+
+       sb = get_super(bdev);
+
+       /* If super_block has been already frozen, return. */
+       if (sb && sb->s_frozen != SB_UNFROZEN) {
+               drop_super(sb);
+               clear_bit(BD_FREEZE_OP, &bdev->bd_state);
+               return sb;
+       }
+
+       if (sb)
+               drop_super(sb);
+
        down(&bdev->bd_mount_sem);
        sb = get_super(bdev);
        if (sb && !(sb->s_flags & MS_RDONLY)) {
@@ -219,6 +234,8 @@ struct super_block *freeze_bdev(struct b
        }
 
        sync_blockdev(bdev);
+       clear_bit(BD_FREEZE_OP, &bdev->bd_state);
+
        return sb;      /* thaw_bdev releases s->s_umount and bd_mount_sem */
 }
 EXPORT_SYMBOL(freeze_bdev);
@@ -230,8 +247,17 @@ 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)
 {
+
+       if (test_and_set_bit(BD_FREEZE_OP, &bdev->bd_state))
+               return -EBUSY;
+
+       if (sb && sb->s_frozen == SB_UNFROZEN) {
+               clear_bit(BD_FREEZE_OP, &bdev->bd_state);
+               return 0;
+       }
+
        if (sb) {
                BUG_ON(sb->s_bdev != bdev);
 
@@ -244,6 +270,8 @@ void thaw_bdev(struct block_device *bdev
        }
 
        up(&bdev->bd_mount_sem);
+       clear_bit(BD_FREEZE_OP, &bdev->bd_state);
+       return 0;
 }
 EXPORT_SYMBOL(thaw_bdev);
 
diff -uprN -X linux-2.6.26-rc7.org/Documentation/dontdiff 
linux-2.6.26-rc7.org/fs/ioctl.c linux-2.6.26-rc7-freeze/fs/ioc
tl.c
--- linux-2.6.26-rc7.org/fs/ioctl.c     2008-06-25 12:08:14.000000000 +0900
+++ linux-2.6.26-rc7-freeze/fs/ioctl.c  2008-06-25 12:00:41.000000000 +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 +142,49 @@ 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;
+
+       /* 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;
+
+       /* 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 +225,15 @@ 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-rc7.org/Documentation/dontdiff 
linux-2.6.26-rc7.org/include/linux/buffer_head.h linux-2.6.26-
rc7-freeze/include/linux/buffer_head.h
--- linux-2.6.26-rc7.org/include/linux/buffer_head.h    2008-06-25 
12:08:19.000000000 +0900
+++ linux-2.6.26-rc7-freeze/include/linux/buffer_head.h 2008-06-25 
12:00:45.000000000 +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-rc7.org/Documentation/dontdiff 
linux-2.6.26-rc7.org/include/linux/fs.h linux-2.6.26-rc7-freez
e/include/linux/fs.h
--- linux-2.6.26-rc7.org/include/linux/fs.h     2008-06-25 12:08:19.000000000 
+0900
+++ linux-2.6.26-rc7-freeze/include/linux/fs.h  2008-06-30 16:40:49.000000000 
+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)
@@ -494,6 +496,13 @@ int pagecache_write_end(struct file *, s
                                loff_t pos, unsigned len, unsigned copied,
                                struct page *page, void *fsdata);
 
+/*
+ * Bits in block_device.bd_state.
+ */
+enum bd_state {
+       BD_FREEZE_OP    /* In freeze operation */
+};
+
 struct backing_dev_info;
 struct address_space {
        struct inode            *host;          /* owner: inode, block_device */
@@ -547,6 +556,9 @@ struct block_device {
         * care to not mess up bd_private for that case.
         */
        unsigned long           bd_private;
+
+       /* State of the block device. (Used by freeze feature) */
+       unsigned long           bd_state;
 };
 
 /*


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