On Tue, 2021-06-08 at 15:16 +0200, Paolo Bonzini wrote:
> I/O to a disk via read/write is not limited by the number of segments allowed
> by the host adapter; the kernel can split requests if needed, and the limit
> imposed by the host adapter can be very low (256k or so) to avoid that SG_IO
> returns EINVAL if memory is heavily fragmented.
>
> Since this value is only interesting for SG_IO-based I/O, do not include
> it in the max_transfer and only take it into account when patching the
> block limits VPD page in the scsi-generic device.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> block/file-posix.c | 3 +--
> hw/scsi/scsi-generic.c | 6 ++++--
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 536998a1d6..670c577bfe 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1239,8 +1239,7 @@ static void raw_refresh_limits(BlockDriverState *bs,
> Error **errp)
>
> ret = sg_get_max_segments(s->fd);
> if (ret > 0) {
> - bs->bl.max_transfer = MIN(bs->bl.max_transfer,
> - ret * qemu_real_host_page_size);
> + bs->bl.max_iov = ret;
Actually I think that both max transfer size and max segement count,
are only relevant for SCSI passthrough since kernel I think emualates
both for regular I/O, so I think that we shoudn't expose them to qemu at all.
In my version of the patches I removed both bl.max_transfer and bl.max_iov
setup from the file-posix driver and replaced it with bs->bl.max_ioctl_transfer
(you call it max_hw_transfer)
In my version the bl.max_ioctl_transfer is a merged limit of the max transfer
size
and the max iovec number.
https://www.mail-archive.com/qemu-devel@nongnu.org/msg768264.html
Best regards,
Maxim Levitsky
> }
> }
>
> diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
> index 98c30c5d5c..82e1e2ee79 100644
> --- a/hw/scsi/scsi-generic.c
> +++ b/hw/scsi/scsi-generic.c
> @@ -179,10 +179,12 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq
> *r, SCSIDevice *s)
> (r->req.cmd.buf[1] & 0x01)) {
> page = r->req.cmd.buf[2];
> if (page == 0xb0) {
> - uint32_t max_transfer =
> - blk_get_max_transfer(s->conf.blk) / s->blocksize;
> + uint32_t max_transfer = blk_get_max_transfer(s->conf.blk);
> + uint32_t max_iov = blk_get_max_iov(s->conf.blk);
>
> assert(max_transfer);
> + max_transfer = MIN_NON_ZERO(max_transfer, max_iov *
> qemu_real_host_page_size)
> + / s->blocksize;
> stl_be_p(&r->buf[8], max_transfer);
> /* Also take care of the opt xfer len. */
> stl_be_p(&r->buf[12],
