Re: [PATCH v3 4/5] block: use blk_get_max_ioctl_transfer for SCSI passthrough

[Max Reitz]

On 17.12.20 17:56, Maxim Levitsky wrote:
> Switch file-posix to expose only the max_ioctl_transfer limit.
>
> Let the iscsi driver work as it did before since it is bound by the transfer
> limit in both regular read/write and in SCSI passthrough case.
>
> Switch the scsi-disk and scsi-block drivers to read the SG max transfer limits
> using the new blk_get_max_ioctl_transfer interface.
>
>
> Fixes: 867eccfed8 ("file-posix: Use max transfer length/segment count only for SCSI 
> passthrough")
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>   block/file-posix.c     | 7 ++++---
>   block/iscsi.c          | 1 +
>   hw/scsi/scsi-generic.c | 4 ++--
>   3 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 2bf4d095a7..c34a7a9599 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1282,13 +1282,14 @@ static void hdev_refresh_limits(BlockDriverState *bs, 
> Error **errp)
>                          get_max_transfer_length(s->fd);
>   
>       if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
> -        bs->bl.max_transfer = pow2floor(ret);
> +        bs->bl.max_ioctl_transfer = pow2floor(ret);
>       }
>   
>       ret = bs->sg ? sg_get_max_segments(s->fd) : get_max_segments(s->fd);
>       if (ret > 0) {
> -        bs->bl.max_transfer = MIN_NON_ZERO(bs->bl.max_transfer,
> -                                           ret * qemu_real_host_page_size);
> +        bs->bl.max_ioctl_transfer =
> +            MIN_NON_ZERO(bs->bl.max_ioctl_transfer,
> +                         ret * qemu_real_host_page_size);
>       }

Do non-SG devices even have a max transfer length then?  I would’ve 
thought max_ioctl_transfer simply doesn’t apply to them and so could be 
left 0.


(Rest looks good – from what I can tell...)

Max

>   
>       raw_refresh_limits(bs, errp);