xen-block: fix reporting of discard feature

Commit Message

Denis V. Lunev" via Jan. 18, 2021, 3:33 p.m. UTC

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/[e-mail]/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 <[e-mail]>
Signed-off-by: Roger Pau Monné <[e-mail]>
---
Cc: Stefano Stabellini <[e-mail]>
Cc: Anthony Perard <[e-mail]>
Cc: Paul Durrant <[e-mail]>
Cc: Kevin Wolf <[e-mail]>
Cc: Max Reitz <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
---
 hw/block/xen-block.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Paul Durrant Jan. 18, 2021, 3:49 p.m. UTC | #1

> -----Original Message-----
> From: Roger Pau Monne <[e-mail]>
> Sent: 18 January 2021 15:34
> To: [e-mail]
> Cc: Roger Pau Monne <[e-mail]>; Arthur Borsboom <[e-mail]>; Stefano
> Stabellini <[e-mail]>; Anthony Perard <[e-mail]>; Paul Durrant
> <[e-mail]>; Kevin Wolf <[e-mail]>; Max Reitz <[e-mail]>; xen-
> [e-mail]; [e-mail]
> 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/[e-mail]/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 <[e-mail]>
> Signed-off-by: Roger Pau Monné <[e-mail]>

Reviewed-by: Paul Durrant <[e-mail]>

> ---
> Cc: Stefano Stabellini <[e-mail]>
> Cc: Anthony Perard <[e-mail]>
> Cc: Paul Durrant <[e-mail]>
> Cc: Kevin Wolf <[e-mail]>
> Cc: Max Reitz <[e-mail]>
> Cc: [e-mail]
> Cc: [e-mail]
> ---
>  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

Kevin Wolf Feb. 15, 2021, 10:51 a.m. UTC | #2

Am 18.01.2021 um 16:49 hat Paul Durrant geschrieben:
> > -----Original Message-----
> > From: Roger Pau Monne <[e-mail]>
> > Sent: 18 January 2021 15:34
> > To: [e-mail]
> > Cc: Roger Pau Monne <[e-mail]>; Arthur Borsboom <[e-mail]>; Stefano
> > Stabellini <[e-mail]>; Anthony Perard <[e-mail]>; Paul Durrant
> > <[e-mail]>; Kevin Wolf <[e-mail]>; Max Reitz <[e-mail]>; xen-
> > [e-mail]; [e-mail]
> > 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/[e-mail]/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 <[e-mail]>
> > Signed-off-by: Roger Pau Monné <[e-mail]>
> 
> Reviewed-by: Paul Durrant <[e-mail]>

Thanks, applied to the block branch.

Kevin

Patch

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);