[PATCH] xfs: Output warning message when discard option was enabled even though the device does not support discard

[PATCH] xfs: Output warning message when discard option was enabled even though the device does not support discard

[Kenjiro Nakayama]

In order to using discard function, it is necessary that not only xfs
is mounted with discard option, but also the discard function is
supported by the device. Current code doesn't output any message when
users mount with discard option on unsupported device, so it is
difficult to notice that it was not enabled actually.

This patch adds the warning message to notice that discard option is
not enabled due to unsupported device when the filesystem is mounted.

Signed-off-by: Kenjiro Nakayama <nakayamakenjiro@gmail.com>
---
 fs/xfs/xfs_super.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index c996f4ae4a5f..60397f9cc786 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -407,6 +407,13 @@ xfs_parseargs(
 		return -EINVAL;
 	}
 #endif
+	if (mp->m_flags & XFS_MOUNT_DISCARD) {
+		struct request_queue *q = bdev_get_queue(sb->s_bdev);
+
+		if (!blk_queue_discard(q))
+			xfs_warn(mp, "mounting with \"discard\" option, but "
+					"the device does not support discard");
+	}
 
 	if ((dsunit && !dswidth) || (!dsunit && dswidth)) {
 		xfs_warn(mp, "sunit and swidth must be specified together");
-- 
2.13.5

Re: [PATCH] xfs: Output warning message when discard option was enabled even though the device does not support discard

[Brian Foster]

On Sun, Sep 17, 2017 at 04:32:52PM +0900, Kenjiro Nakayama wrote:
> In order to using discard function, it is necessary that not only xfs
> is mounted with discard option, but also the discard function is
> supported by the device. Current code doesn't output any message when
> users mount with discard option on unsupported device, so it is
> difficult to notice that it was not enabled actually.
> 
> This patch adds the warning message to notice that discard option is
> not enabled due to unsupported device when the filesystem is mounted.
> 
> Signed-off-by: Kenjiro Nakayama <nakayamakenjiro@gmail.com>
> ---
>  fs/xfs/xfs_super.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index c996f4ae4a5f..60397f9cc786 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -407,6 +407,13 @@ xfs_parseargs(
>  		return -EINVAL;
>  	}
>  #endif
> +	if (mp->m_flags & XFS_MOUNT_DISCARD) {
> +		struct request_queue *q = bdev_get_queue(sb->s_bdev);
> +
> +		if (!blk_queue_discard(q))
> +			xfs_warn(mp, "mounting with \"discard\" option, but "
> +					"the device does not support discard");
> +	}

Seems reasonable to me. Though perhaps we should move this into
xfs_fs_fill_super() (where we have a similar check for DAX support of
the underlying device) and also clear the discard flag so we don't
continue to queue discards that won't ever succeed.

Brian

>  
>  	if ((dsunit && !dswidth) || (!dsunit && dswidth)) {
>  		xfs_warn(mp, "sunit and swidth must be specified together");
> -- 
> 2.13.5
> 
> --
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