RE: [PATCH] xen-block: fix reporting of discard feature

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Sent: 18 January 2021 15:34
> To: qemu-devel@xxxxxxxxxx
> Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>; Arthur Borsboom 
> <arthurborsboom@xxxxxxxxx>; Stefano
> Stabellini <sstabellini@xxxxxxxxxx>; Anthony Perard 
> <anthony.perard@xxxxxxxxxx>; Paul Durrant
> <paul@xxxxxxx>; Kevin Wolf <kwolf@xxxxxxxxxx>; Max Reitz <mreitz@xxxxxxxxxx>; 
> xen-
> devel@xxxxxxxxxxxxxxxxxxxx; qemu-block@xxxxxxxxxx
> Subject: [PATCH] xen-block: fix reporting of discard feature
> 
> Linux blkfront expects both "discard-granularity" and
> "discard-alignment" present on xenbus in order to properly enable the
> feature, not exposing "discard-alignment" left some Linux blkfront
> versions with a broken discard setup. This has also been addressed in
> Linux with:
> 
> https://lore.kernel.org/lkml/20210118151528.81668-1-roger.pau@xxxxxxxxxx/T/#u
> 
> Fix QEMU to report a "discard-alignment" of 0, in order for it to work
> with older Linux frontends.
> 
> Reported-by: Arthur Borsboom <arthurborsboom@xxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Paul Durrant <paul@xxxxxxx>

> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> Cc: Paul Durrant <paul@xxxxxxx>
> Cc: Kevin Wolf <kwolf@xxxxxxxxxx>
> Cc: Max Reitz <mreitz@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: qemu-block@xxxxxxxxxx
> ---
>  hw/block/xen-block.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
> index 718d886e5c..246d9c23a2 100644
> --- a/hw/block/xen-block.c
> +++ b/hw/block/xen-block.c
> @@ -253,6 +253,7 @@ static void xen_block_realize(XenDevice *xendev, Error 
> **errp)
>          xen_device_backend_printf(xendev, "feature-discard", "%u", 1);
>          xen_device_backend_printf(xendev, "discard-granularity", "%u",
>                                    conf->discard_granularity);
> +        xen_device_backend_printf(xendev, "discard-alignment", "%u", 0);
>      }
> 
>      xen_device_backend_printf(xendev, "feature-flush-cache", "%u", 1);
> --
> 2.29.2