[PATCH] btrfs: introduce BTRFS_IOC_CHECK_DEV_EXCL_OPS ioctl to check dev excl op

[Anand Jain <anand.jain@oracle.com>]

This patch provides an ioctl to check if the FS is performing
any device exclusive operations like device add remove balance
etc. Basically any operation which will set
fs_info->mutually_exclusive_operation_running to true

This will be necessary for any user cli which has to know
the state before putting long running commands to background.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/ioctl.c           |   10 ++++++++++
 include/uapi/linux/btrfs.h |    1 +
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 89f346c..3544a90 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4420,6 +4420,14 @@ out_unlock:
 	return ret;
 }
 
+static int btrfs_ioctl_check_dev_excl_op(struct btrfs_root *root,
+		void __user *arg)
+{
+	if (atomic_read(&root->fs_info->mutually_exclusive_operation_running))
+		return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
+	return 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {
@@ -4532,6 +4540,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_set_fslabel(file, argp);
 	case BTRFS_IOC_FILE_EXTENT_SAME:
 		return btrfs_ioctl_file_extent_same(file, argp);
+	case BTRFS_IOC_CHECK_DEV_EXCL_OPS:
+		return btrfs_ioctl_check_dev_excl_op(root, NULL);
 	}
 
 	return -ENOTTY;
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 90d7bd9..a4fa6eb 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -606,5 +606,6 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 				    struct btrfs_ioctl_dev_replace_args)
 #define BTRFS_IOC_FILE_EXTENT_SAME _IOWR(BTRFS_IOCTL_MAGIC, 54, \
 					 struct btrfs_ioctl_same_args)
+#define BTRFS_IOC_CHECK_DEV_EXCL_OPS _IO(BTRFS_IOCTL_MAGIC, 56)
 
 #endif /* _UAPI_LINUX_BTRFS_H */
-- 
1.7.1