Re: [Qemu-devel] [PATCH v2] scsi-disk: Don't enlarge min_io_size to max_io_size

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 1976 bytes --]

On Wed, Mar 28, 2018 at 12:41:41AM +0800, Fam Zheng wrote:
> Some backends report big max_io_sectors. Making min_io_size the same
> value in this case will make it impossible for guest to align memory,
> therefore the disk may not be usable at all.
> 
> Do not enlarge them when they are zero.
> 
> Reported-by: David Gibson <dgibson@redhat.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>

Tested-by: David Gibson <david@gibson.dropbear.id.au>

With this patch applied, I was able to successfully install a ppc64le
guest again.

> 
> ---
> 
> v2: Leave the values alone if zero. [Paolo]
>     At least we can consult block layer for a slightly more sensible
>     opt_io_size, but that's for another patch.
> ---
>  hw/scsi/scsi-disk.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
> index f5ab767ab5..f8ed8cf2b4 100644
> --- a/hw/scsi/scsi-disk.c
> +++ b/hw/scsi/scsi-disk.c
> @@ -714,10 +714,12 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, uint8_t *outbuf)
>  
>                  /* min_io_size and opt_io_size can't be greater than
>                   * max_io_sectors */
> -                min_io_size =
> -                    MIN_NON_ZERO(min_io_size, max_io_sectors);
> -                opt_io_size =
> -                    MIN_NON_ZERO(opt_io_size, max_io_sectors);
> +                if (min_io_size) {
> +                    min_io_size = MIN(min_io_size, max_io_sectors);
> +                }
> +                if (opt_io_size) {
> +                    opt_io_size = MIN(opt_io_size, max_io_sectors);
> +                }
>              }
>              /* required VPD size with unmap support */
>              buflen = 0x40;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]