Yes, the question is whether it still exists...
Paolo
El jue., 23 sept. 2021 16:48, Christian Borntraeger <borntrae...@de.ibm.com>
escribió:
>
>
> Am 23.09.21 um 15:04 schrieb Paolo Bonzini:
> > Linux limits the size of iovecs to 1024 (UIO_MAXIOV in the kernel
> > sources, IOV_MAX in POSIX). Because of this, on some host adapters
> > requests with many iovecs are rejected with -EINVAL by the
> > io_submit() or readv()/writev() system calls.
> >
> > In fact, the same limit applies to SG_IO as well. To fix both the
> > EINVAL and the possible performance issues from using fewer iovecs
> > than allowed by Linux (some HBAs have max_segments as low as 128),
> > introduce a separate entry in BlockLimits to hold the max_segments
> > value from sysfs. This new limit is used only for SG_IO and clamped
> > to bs->bl.max_iov anyway, just like max_hw_transfer is clamped to
> > bs->bl.max_transfer.
> >
> > Reported-by: Halil Pasic <pa...@linux.ibm.com>
> > Cc: Hanna Reitz <hre...@redhat.com>
> > Cc: Kevin Wolf <kw...@redhat.com>
> > Cc: qemu-bl...@nongnu.org
> > Fixes: 18473467d5 ("file-posix: try BLKSECTGET on block devices too, do
> not round to power of 2", 2021-06-25)
>
> This sneaked in shortly before the 6.1 release (between rc0 and rc1 I
> think).
> Shouldnt that go to stable in cass this still exist?
>
>
> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> > ---
> > block/block-backend.c | 6 ++++++
> > block/file-posix.c | 2 +-
> > block/io.c | 1 +
> > hw/scsi/scsi-generic.c | 2 +-
> > include/block/block_int.h | 7 +++++++
> > include/sysemu/block-backend.h | 1 +
> > 6 files changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/block-backend.c b/block/block-backend.c
> > index 6140d133e2..ba2b5ebb10 100644
> > --- a/block/block-backend.c
> > +++ b/block/block-backend.c
> > @@ -1986,6 +1986,12 @@ uint32_t blk_get_max_transfer(BlockBackend *blk)
> > return ROUND_DOWN(max, blk_get_request_alignment(blk));
> > }
> >
> > +int blk_get_max_hw_iov(BlockBackend *blk)
> > +{
> > + return MIN_NON_ZERO(blk->root->bs->bl.max_hw_iov,
> > + blk->root->bs->bl.max_iov);
> > +}
> > +
> > int blk_get_max_iov(BlockBackend *blk)
> > {
> > return blk->root->bs->bl.max_iov;
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index cb9bffe047..1567edb3d5 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1273,7 +1273,7 @@ static void raw_refresh_limits(BlockDriverState
> *bs, Error **errp)
> >
> > ret = hdev_get_max_segments(s->fd, &st);
> > if (ret > 0) {
> > - bs->bl.max_iov = ret;
> > + bs->bl.max_hw_iov = ret;
> > }
> > }
> > }
> > diff --git a/block/io.c b/block/io.c
> > index a19942718b..f38e7f81d8 100644
> > --- a/block/io.c
> > +++ b/block/io.c
> > @@ -136,6 +136,7 @@ static void bdrv_merge_limits(BlockLimits *dst,
> const BlockLimits *src)
> > dst->min_mem_alignment = MAX(dst->min_mem_alignment,
> > src->min_mem_alignment);
> > dst->max_iov = MIN_NON_ZERO(dst->max_iov, src->max_iov);
> > + dst->max_hw_iov = MIN_NON_ZERO(dst->max_hw_iov, src->max_hw_iov);
> > }
> >
> > typedef struct BdrvRefreshLimitsState {
> > diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
> > index 665baf900e..0306ccc7b1 100644
> > --- a/hw/scsi/scsi-generic.c
> > +++ b/hw/scsi/scsi-generic.c
> > @@ -180,7 +180,7 @@ static int scsi_handle_inquiry_reply(SCSIGenericReq
> *r, SCSIDevice *s, int len)
> > page = r->req.cmd.buf[2];
> > if (page == 0xb0) {
> > uint64_t max_transfer =
> blk_get_max_hw_transfer(s->conf.blk);
> > - uint32_t max_iov = blk_get_max_iov(s->conf.blk);
> > + uint32_t max_iov = blk_get_max_hw_iov(s->conf.blk);
> >
> > assert(max_transfer);
> > max_transfer = MIN_NON_ZERO(max_transfer, max_iov *
> qemu_real_host_page_size)
> > diff --git a/include/block/block_int.h b/include/block/block_int.h
> > index f1a54db0f8..c31cbd034a 100644
> > --- a/include/block/block_int.h
> > +++ b/include/block/block_int.h
> > @@ -702,6 +702,13 @@ typedef struct BlockLimits {
> > */
> > uint64_t max_hw_transfer;
> >
> > + /* Maximal number of scatter/gather elements allowed by the
> hardware.
> > + * Applies whenever transfers to the device bypass the kernel I/O
> > + * scheduler, for example with SG_IO. If larger than max_iov
> > + * or if zero, blk_get_max_hw_iov will fall back to max_iov.
> > + */
> > + int max_hw_iov;
> > +
> > /* memory alignment, in bytes so that no bounce buffer is needed */
> > size_t min_mem_alignment;
> >
> > diff --git a/include/sysemu/block-backend.h
> b/include/sysemu/block-backend.h
> > index 29d4fdbf63..82bae55161 100644
> > --- a/include/sysemu/block-backend.h
> > +++ b/include/sysemu/block-backend.h
> > @@ -211,6 +211,7 @@ uint32_t blk_get_request_alignment(BlockBackend
> *blk);
> > uint32_t blk_get_max_transfer(BlockBackend *blk);
> > uint64_t blk_get_max_hw_transfer(BlockBackend *blk);
> > int blk_get_max_iov(BlockBackend *blk);
> > +int blk_get_max_hw_iov(BlockBackend *blk);
> > void blk_set_guest_block_size(BlockBackend *blk, int align);
> > void *blk_try_blockalign(BlockBackend *blk, size_t size);
> > void *blk_blockalign(BlockBackend *blk, size_t size);
> >
>
>
