[Virtio-fs] [PATCH v2 0/3] virtio: increase VIRTQUEUE_MAX_SIZE to 32k
Stefan Hajnoczi
stefanha at redhat.com
Thu Oct 7 05:23:59 UTC 2021
On Mon, Oct 04, 2021 at 09:38:00PM +0200, Christian Schoenebeck wrote:
> At the moment the maximum transfer size with virtio is limited to 4M
> (1024 * PAGE_SIZE). This series raises this limit to its maximum
> theoretical possible transfer size of 128M (32k pages) according to the
> virtio specs:
>
> https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-240006
Hi Christian,
I took a quick look at the code:
- The Linux 9p driver restricts descriptor chains to 128 elements
(net/9p/trans_virtio.c:VIRTQUEUE_NUM)
- The QEMU 9pfs code passes iovecs directly to preadv(2) and will fail
with EINVAL when called with more than IOV_MAX iovecs
(hw/9pfs/9p.c:v9fs_read())
Unless I misunderstood the code, neither side can take advantage of the
new 32k descriptor chain limit?
Thanks,
Stefan
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