[PATCH] btrfs: add comment about BTRFS_FS_EXCL_OP

[PATCH] btrfs: add comment about BTRFS_FS_EXCL_OP

[Anand Jain]

Adds comments about BTRFS_FS_EXCL_OP to existing comments
about the device locks.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/volumes.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3a3912a9dec9..18306165ffaa 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -202,6 +202,22 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
  *   device_list_mutex
  *     chunk_mutex
  *   balance_mutex
+ *
+ * BTRFS_FS_EXCL_OP
+ * ----------------
+ * Maintains the exclusivity of the following device operations.
+ *
+ * - Balance (*)
+ * - Add
+ * - Remove
+ * - Replace (*)
+ * - Resize
+ *
+ * The device operation with (*) indicate it can continue after a CLI pause
+ * (only balance can be paused using CLI) or remount or unmount-mount sequence
+ * or a power-recycle, as long as the FS is still writeable. And during the
+ * course of the pause, the BTRFS_FS_EXCL_OP remains set. BTRFS_FS_EXCL_OP flag
+ * is set and cleared using atomic functions.
  */
 
 DEFINE_MUTEX(uuid_mutex);
-- 
2.15.0

Re: [PATCH] btrfs: add comment about BTRFS_FS_EXCL_OP

[David Sterba]

On Mon, Apr 16, 2018 at 06:28:31PM +0800, Anand Jain wrote:
> Adds comments about BTRFS_FS_EXCL_OP to existing comments
> about the device locks.

Thanks, a few comments below.

> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/volumes.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 3a3912a9dec9..18306165ffaa 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -202,6 +202,22 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
>   *   device_list_mutex
>   *     chunk_mutex
>   *   balance_mutex
> + *
> + * BTRFS_FS_EXCL_OP
> + * ----------------
> + * Maintains the exclusivity of the following device operations.
> + *
> + * - Balance (*)
> + * - Add

device add

> + * - Remove

device remove

> + * - Replace (*)

device replace

> + * - Resize
> + *
> + * The device operation with (*) indicate it can continue after a CLI pause
> + * (only balance can be paused using CLI) or remount or unmount-mount sequence
> + * or a power-recycle, as long as the FS is still writeable. And during the

this would be more readable if is' a bullet list like above

> + * course of the pause, the BTRFS_FS_EXCL_OP remains set. BTRFS_FS_EXCL_OP flag
> + * is set and cleared using atomic functions.

Please rephrase that without the CLI and use 'ioctl' instead, as this
is the interface.

>   */
>  
>  DEFINE_MUTEX(uuid_mutex);