Re: [PATCH v2] xen-blkfront: allow discard-* nodes to be optional

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

Forgot to Cc stable for the Fixes tag. Doing it now.

On Tue, Jan 19, 2021 at 11:57:27AM +0100, Roger Pau Monne wrote:
> This is inline with the specification described in blkif.h:
> 
>  * discard-granularity: should be set to the physical block size if
>    node is not present.
>  * discard-alignment, discard-secure: should be set to 0 if node not
>    present.
> 
> This was detected as QEMU would only create the discard-granularity
> node but not discard-alignment, and thus the setup done in
> blkfront_setup_discard would fail.
> 
> Fix blkfront_setup_discard to not fail on missing nodes, and also fix
> blkif_set_queue_limits to set the discard granularity to the physical
> block size if none is specified in xenbus.
> 
> Fixes: ed30bf317c5ce ('xen-blkfront: Handle discard requests.')
> Reported-by: Arthur Borsboom <arthurborsboom@xxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: linux-block@xxxxxxxxxxxxxxx
> Cc: Arthur Borsboom <arthurborsboom@xxxxxxxxx>
> ---
> Changes since v2:
>  - Allow all discard-* nodes to be optional.
> ---
>  drivers/block/xen-blkfront.c | 20 +++++++-------------
>  1 file changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 5265975b3fba..e1c6798889f4 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -945,7 +945,8 @@ static void blkif_set_queue_limits(struct blkfront_info 
> *info)
>       if (info->feature_discard) {
>               blk_queue_flag_set(QUEUE_FLAG_DISCARD, rq);
>               blk_queue_max_discard_sectors(rq, get_capacity(gd));
> -             rq->limits.discard_granularity = info->discard_granularity;
> +             rq->limits.discard_granularity = info->discard_granularity ?:
> +                                              info->physical_sector_size;
>               rq->limits.discard_alignment = info->discard_alignment;
>               if (info->feature_secdiscard)
>                       blk_queue_flag_set(QUEUE_FLAG_SECERASE, rq);
> @@ -2179,19 +2180,12 @@ static void blkfront_closing(struct blkfront_info 
> *info)
>  
>  static void blkfront_setup_discard(struct blkfront_info *info)
>  {
> -     int err;
> -     unsigned int discard_granularity;
> -     unsigned int discard_alignment;
> -
>       info->feature_discard = 1;
> -     err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> -             "discard-granularity", "%u", &discard_granularity,
> -             "discard-alignment", "%u", &discard_alignment,
> -             NULL);
> -     if (!err) {
> -             info->discard_granularity = discard_granularity;
> -             info->discard_alignment = discard_alignment;
> -     }
> +     info->discard_granularity = xenbus_read_unsigned(info->xbdev->otherend,
> +                                                      "discard-granularity",
> +                                                      0);
> +     info->discard_alignment = xenbus_read_unsigned(info->xbdev->otherend,
> +                                                    "discard-alignment", 0);
>       info->feature_secdiscard =
>               !!xenbus_read_unsigned(info->xbdev->otherend, "discard-secure",
>                                      0);
> -- 
> 2.29.2
>