[PATCH 4/4] filesystem freeze: add ISFROZEN ioctl

["Fernando Luis Vázquez Cao" <fernando@oss.ntt.co.jp>]

The ISFROZEN ioctl can be use by HA and monitoring software to check
the freeze state of a filesystem.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
---

diff -urNp linux-2.6.31-rc7-orig/fs/block_dev.c linux-2.6.31-rc7/fs/block_dev.c
--- linux-2.6.31-rc7-orig/fs/block_dev.c	2009-08-27 14:48:12.000000000 +0900
+++ linux-2.6.31-rc7/fs/block_dev.c	2009-08-27 18:49:46.000000000 +0900
@@ -334,6 +334,21 @@ out_unlock:
  }
  EXPORT_SYMBOL(thaw_bdev);

+/**
+ *
+ */
+int isfrozen_bdev(struct block_device *bdev, struct super_block *sb)
+{
+	int ret;
+
+	mutex_lock(&bdev->bd_fsfreeze_mutex);
+	ret = sb->s_frozen > SB_UNFROZEN ? 1:0;
+	mutex_unlock(&bdev->bd_fsfreeze_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL(isfrozen_bdev);
+
  static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
  {
  	return block_write_full_page(page, blkdev_get_block, wbc);
diff -urNp linux-2.6.31-rc7-orig/fs/ioctl.c linux-2.6.31-rc7/fs/ioctl.c
--- linux-2.6.31-rc7-orig/fs/ioctl.c	2009-08-27 10:08:00.000000000 +0900
+++ linux-2.6.31-rc7/fs/ioctl.c	2009-08-27 18:49:17.000000000 +0900
@@ -536,6 +536,20 @@ static int ioctl_fsthaw(struct file *fil
  	return thaw_bdev(sb->s_bdev, sb);
  }

+static int ioctl_isfrozen(struct file *filp)
+{
+	struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	/* If a blockdevice-backed filesystem isn't specified, return EINVAL. */
+	if (sb->s_bdev == NULL)
+		return -EINVAL;
+
+	return isfrozen_bdev(sb->s_bdev, sb);
+}
+
  /*
   * When you add any new common ioctls to the switches above and below
   * please update compat_sys_ioctl() too.
@@ -586,6 +600,12 @@ int do_vfs_ioctl(struct file *filp, unsi
  		error = ioctl_fsthaw(filp);
  		break;

+	case FIISFROZEN:
+		error = ioctl_isfrozen(filp);
+		if (error >= 0)
+			return put_user(error, (int __user *)arg);
+		break;
+
  	case FS_IOC_FIEMAP:
  		return ioctl_fiemap(filp, arg);

diff -urNp linux-2.6.31-rc7-orig/include/linux/fs.h linux-2.6.31-rc7/include/linux/fs.h
--- linux-2.6.31-rc7-orig/include/linux/fs.h	2009-08-27 14:48:12.000000000 +0900
+++ linux-2.6.31-rc7/include/linux/fs.h	2009-08-27 16:33:19.000000000 +0900
@@ -306,6 +306,7 @@ struct inodes_stat_t {
  #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 FIISFROZEN	_IOWR('X', 121, int)	/* Is frozen? */

  #define	FS_IOC_GETFLAGS			_IOR('f', 1, long)
  #define	FS_IOC_SETFLAGS			_IOW('f', 2, long)
@@ -1955,6 +1956,7 @@ extern int sync_blockdev(struct block_de
  extern struct super_block *freeze_bdev(struct block_device *);
  extern void emergency_thaw_all(void);
  extern int thaw_bdev(struct block_device *bdev, struct super_block *sb);
+extern int isfrozen_bdev(struct block_device *bdev, struct super_block *sb);
  extern int fsync_bdev(struct block_device *);
  #else
  static inline void bd_forget(struct inode *inode) {}
@@ -1970,6 +1972,12 @@ static inline int thaw_bdev(struct block
  {
  	return 0;
  }
+
+extern int isfrozen_bdev(struct block_device *bdev, struct super_block *sb)
+{
+	return 0;
+}
+
  #endif
  extern int sync_filesystem(struct super_block *);
  extern const struct file_operations def_blk_fops;