Re: [PATCH] block: introduce max_hw_iov for use in scsi-generic

[Kevin Wolf]

Am 23.09.2021 um 15:04 hat Paolo Bonzini geschrieben:
> 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 <pasic@linux.ibm.com>
> Cc: Hanna Reitz <hreitz@redhat.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: qemu-block@nongnu.org
> Fixes: 18473467d5 ("file-posix: try BLKSECTGET on block devices too, do not 
> round to power of 2", 2021-06-25)
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks, applied to the block branch.

Kevin