Re: [PATCH] btrfs: device stat, log when zeroed assist audit

[Nikolay Borisov <nborisov@suse.com>]

On 10.01.20 г. 6:26 ч., Anand Jain wrote:
> We had a report indicating that some read errors aren't reported by
> the device stats in the userland. It is important to have the errors
> reported in the device stat as user land scripts might depend on it to
> take the reasonable corrective actions. But to debug these issue we need
> to be really sure that request to reset the device stat did not come
> from the userland itself. So log an info message when device error reset
> happens.
> 
> For example:
>  BTRFS info (device sdc): device stats zeroed by btrfs (9223)
> 
> Reported-by: philip@philip-seeger.de
> Link: https://www.spinics.net/lists/linux-btrfs/msg96528.html
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  BTRFS info (device sdc): device stats zeroed by btrfs (9223)
> The last words are name and pid of the process, unfortunately it came out
> as 'by btrfs'. At some point if there is a python and lib to reset it
> would change, otherwise its going to be 'by btrfs', I am ok with it,
> if otherwise please suggest the alternative.

This patch itself is OK but is not related to what Philip has reported.
The issue there is the fact we only record errors for 2 specific retvals
from block layer.

> 
>  fs/btrfs/volumes.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index eb55df0d4038..6fd90270e2c7 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -7324,6 +7324,8 @@ int btrfs_get_dev_stats(struct btrfs_fs_info *fs_info,
>  			else
>  				btrfs_dev_stat_set(dev, i, 0);
>  		}
> +		btrfs_info(fs_info, "device stats zeroed by %s (%d)",
> +			   current->comm, task_pid_nr(current));
>  	} else {
>  		for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
>  			if (stats->nr_items > i)
>