linux-kernel - Re: [PATCH 0/2] xen-blk{front,back}: Advertise feature-persistent as user requested

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Date:   Fri, 26 Aug 2022 09:15:33 +0200
From:   Juergen Gross <jgross@...e.com>
To:     SeongJae Park <sj@...nel.org>, roger.pau@...rix.com
Cc:     marmarek@...isiblethingslab.com, mheyne@...zon.de,
        xen-devel@...ts.xenproject.org, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] xen-blk{front,back}: Advertise feature-persistent as
 user requested

On 25.08.22 18:15, SeongJae Park wrote:
> Commit e94c6101e151 ("xen-blkback: Apply 'feature_persistent' parameter
> when connect") made blkback to advertise its support of the persistent
> grants feature only if the user sets the 'feature_persistent' parameter
> of the driver and the frontend advertised its support of the feature.
> However, following commit 402c43ea6b34 ("xen-blkfront: Apply
> 'feature_persistent' parameter when connect") made the blkfront to work
> in the same way.  That is, blkfront also advertises its support of the
> persistent grants feature only if the user sets the 'feature_persistent'
> parameter of the driver and the backend advertised its support of the
> feature.
> 
> Hence blkback and blkfront will never advertise their support of the
> feature but wait until the other advertises the support, even though
> users set the 'feature_persistent' parameters of the drivers.  As a
> result, the persistent grants feature is disabled always regardless of
> the 'feature_persistent' values[1].
> 
> The problem comes from the misuse of the semantic of the advertisement
> of the feature.  The advertisement of the feature should means only
> availability of the feature not the decision for using the feature.
> However, current behavior is working in the wrong way.
> 
> This patchset fixes the issue by making both blkback and blkfront
> advertise their support of the feature as user requested via
> 'feature_persistent' parameter regardless of the otherend's support of
> the feature.
> 
> [1] https://lore.kernel.org/xen-devel/bd818aba-4857-bc07-dc8a-e9b2f8c5f7cd@suse.com/
> 
> SeongJae Park (2):
>    xen-blkback: Advertise feature-persistent as user requested
>    xen-blkfront: Advertise feature-persistent as user requested
> 
>   drivers/block/xen-blkback/common.h | 3 +++
>   drivers/block/xen-blkback/xenbus.c | 6 ++++--
>   drivers/block/xen-blkfront.c       | 8 ++++++--
>   3 files changed, 13 insertions(+), 4 deletions(-)
> 

For the series:

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen

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