Re: [PATCH 1/3 v2 RFC] btrfs: total_devices vs num_devices

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

  Any comments on this set of patches ?

Thanks, Anand


On 07/03/2014 23:48, Anand Jain wrote:
> The intended usage of total_devices and num_devices
> should be recorded in the comments so that these
> two counters can be used correctly as originally
> intended.
>
> As of now there appears to be slight deviations/bugs
> from the original intention, the bugs are apparent
> that num_devices does not count seed devices where
> as total_devices does, but total_devices does not
> count the replacing devices where as num_devices does.
>
> So in this situation the ioctl(BTRFS_IOC_DEVICES_READY)
> will fails when there is seed FS. Next, applications
> using ioctl(BTRFS_IOC_FS_INFO) and ioctl(BTRFS_IOC_DEV_INFO)
> in conjunction to allocate the slots will also fail
> as former depend on the num_devices where as latter
> would match total_devices (except when replace is running).
>
> This patch will help have the clarity on usage
> of these two counter so that bugs related to this can
> be fixed.
>
> Signed-off-by: Anand Jain <Anand.Jain@oracle.com>
> ---
> v2: edit commit
>
>   fs/btrfs/volumes.h | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 91b7596..99c71aa 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -121,12 +121,18 @@ struct btrfs_fs_devices {
>   	/* the device with this id has the most recent copy of the super */
>   	u64 latest_devid;
>   	u64 latest_trans;
> +	/* num_devices contains run time count of devices which are part
> +	 * of this FSID. (the FS devices + replacing devices + ?
> +	 */
>   	u64 num_devices;
>   	u64 open_devices;
>   	u64 rw_devices;
>   	u64 missing_devices;
>   	u64 total_rw_bytes;
>   	u64 num_can_discard;
> +	/* total_devices contains static recorded count of device which
> +	 * are part of this FSID. (the FS devices + seed devices + ?
> +	 */
>   	u64 total_devices;
>   	struct block_device *latest_bdev;
>
>