On Fri, Jan 11, 2013 at 01:39:40PM +0100, Kevin Wolf wrote:
> Am 10.01.2013 17:48, schrieb Stefan Hajnoczi:
> > O_DIRECT on Linux has alignment requirements on I/O buffers and
> > misaligned requests result in -EINVAL. The Linux virtio_blk guest
> > driver usually submits aligned requests so I forgot to handle misaligned
> > requests.
> >
> > It turns out that virtio-win guest drivers submit misaligned requests.
> > Handle them using a bounce buffer that meets alignment requirements.
> >
> > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> > ---
> > hw/dataplane/virtio-blk.c | 36 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 36 insertions(+)
> >
> > diff --git a/hw/dataplane/virtio-blk.c b/hw/dataplane/virtio-blk.c
> > index a6696b8..991ab5f 100644
> > --- a/hw/dataplane/virtio-blk.c
> > +++ b/hw/dataplane/virtio-blk.c
> > @@ -34,6 +34,8 @@ typedef struct {
> > struct iocb iocb; /* Linux AIO control block */
> > QEMUIOVector *inhdr; /* iovecs for virtio_blk_inhdr */
> > unsigned int head; /* vring descriptor index */
> > + void *bounce_buffer; /* used if guest buffers are unaligned
> > */
> > + QEMUIOVector *read_qiov; /* for read completion /w bounce
> > buffer */
> > } VirtIOBlockRequest;
> >
> > struct VirtIOBlockDataPlane {
> > @@ -89,6 +91,15 @@ static void complete_request(struct iocb *iocb, ssize_t
> > ret, void *opaque)
> >
> > trace_virtio_blk_data_plane_complete_request(s, req->head, ret);
> >
> > + if (req->read_qiov) {
> > + assert(req->bounce_buffer);
> > + qemu_iovec_to_buf(req->read_qiov, 0, req->bounce_buffer, len);
>
> Shouldn't it be qemu_iovec_from_buf()?
>
> Makes me wonder if qtest cases might be doable...
>
> > + qemu_iovec_destroy(req->read_qiov);
> > + g_slice_free(QEMUIOVector, req->read_qiov);
> > + }
> > +
> > + qemu_vfree(req->bounce_buffer);
> > +
> > qemu_iovec_from_buf(req->inhdr, 0, &hdr, sizeof(hdr));
> > qemu_iovec_destroy(req->inhdr);
> > g_slice_free(QEMUIOVector, req->inhdr);
> > @@ -136,6 +147,29 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool
> > read,
> > QEMUIOVector *inhdr)
> > {
> > struct iocb *iocb;
> > + QEMUIOVector qiov;
> > + struct iovec bounce_iov;
> > + void *bounce_buffer = NULL;
> > + QEMUIOVector *read_qiov = NULL;
> > +
> > + qemu_iovec_init_external(&qiov, iov, iov_cnt);
> > + if (!bdrv_qiov_is_aligned(s->blk->conf.bs, &qiov)) {
> > + /* Redirect I/O to aligned bounce buffer */
> > + bounce_buffer = qemu_blockalign(s->blk->conf.bs, qiov.size);
> > + bounce_iov.iov_base = bounce_buffer;
> > + bounce_iov.iov_len = qiov.size;
> > + iov = &bounce_iov;
> > + iov_cnt = 1;
> > +
> > + if (read) {
> > + /* Need to copy back from bounce buffer on completion */
> > + read_qiov = g_slice_new(QEMUIOVector);
> > + qemu_iovec_init(read_qiov, iov_cnt);
> > + qemu_iovec_concat_iov(read_qiov, iov, iov_cnt, 0, qiov.size);
>
> This would have to be the original iov and iov_cnt, but they are already
> overwritten here.
Good point. What's really weird is that I tested this with a Windows
guest - probably the buffer cache fooled me so I didn't notice read was
completely broken.
Stefan
