[PATCH v4 2/7] scsi-generic: pass max_segments via max_iov field in BlockLimits
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
---
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;
}
}
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],
--
2.31.1
Re: [PATCH v4 2/7] scsi-generic: pass max_segments via max_iov field in BlockLimits
On Tue, Jun 08, 2021 at 03:16:29PM +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. to avoid SG_IO returning EINVAL > > 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 > --- > block/file-posix.c | 3 +-- > hw/scsi/scsi-generic.c | 6 -- > 2 files changed, 5 insertions(+), 4 deletions(-) > Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
Re: [PATCH v4 2/7] scsi-generic: pass max_segments via max_iov field in BlockLimits
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
> ---
> 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],
