Re: [Qemu-devel] [PATCH 3/3] block: get max_transfer limit for char (scsi-generic) devices

[Fam Zheng <famz@redhat.com>]

On Mon, 01/16 22:12, Eric Farman wrote:
> Commit 6f607174 introduced a routine to get the maximum number
> of bytes for a single I/O transfer for block devices, however
> scsi generic devices are character devices, not block.  Add
> a condition for this, with slightly different logic because
> the value is already in bytes, and need not be converted from
> blocks as happens for block devices.
> 
> Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
> ---
>  block/file-posix.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 2115155..c0843c2 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -679,6 +679,13 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
>              if (ret > 0 && ret <= BDRV_REQUEST_MAX_SECTORS) {
>                  bs->bl.max_transfer = pow2floor(ret << BDRV_SECTOR_BITS);
>              }
> +        } else if (S_ISCHR(st.st_mode)) {
> +            /* sg returns transfer length in bytes already */
> +            int ret = hdev_get_max_transfer_length(bs, s->fd);
> +            if (ret > 0 &&
> +                (ret >> BDRV_SECTOR_BITS) <= BDRV_REQUEST_MAX_SECTORS) {
> +                bs->bl.max_transfer = pow2floor(ret);
> +            }

Please keep the sectors/bytes quirk in hdev_get_max_transfer_length and always
return bytes from there.

Fam

>          }
>      }
>  
> -- 
> 2.8.4
> 
>