Re: [PATCH v2 2/2] block/io: skip head/tail requests on EINVAL

[Hanna Czenczek <hreitz@redhat.com>]

On 10.04.25 20:41, Stefan Hajnoczi wrote:
> When guests send misaligned discard requests, the block layer breaks
> them up into a misaligned head, an aligned main body, and a misaligned
> tail.
>
> The file-posix block driver on Linux returns -EINVAL on misaligned
> discard requests. This causes bdrv_co_pdiscard() to fail and guests
> configured with werror=stop will pause.
>
> Add a special case for misaligned head/tail requests. Simply continue
> when EINVAL is encountered so that the aligned main body of the request
> can be completed and the guest is not paused. This is the best we can do
> when guest discard limits do not match the host discard limits.
>
> Fixes: https://issues.redhat.com/browse/RHEL-86032
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   block/io.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/block/io.c b/block/io.c
> index 1ba8d1aeea..a0d0b31a3e 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -3180,7 +3180,11 @@ int coroutine_fn bdrv_co_pdiscard(BdrvChild *child, int64_t offset,
>               }
>           }
>           if (ret && ret != -ENOTSUP) {
> -            goto out;
> +            if (ret == -EINVAL && (offset % align != 0 || num % align != 0)) {

Could use `(offset | num) % align != 0`, but either way:

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>

> +                /* Silently skip rejected unaligned head/tail requests */
> +            } else {
> +                goto out; /* bail out */
> +            }
>           }
>   
>           offset += num;