On Thu, May 23, 2024 at 12:30 PM Jonah Palmer <jonah.pal...@oracle.com> wrote: > > > > On 5/22/24 12:07 PM, Eugenio Perez Martin wrote: > > On Mon, May 20, 2024 at 3:01 PM Jonah Palmer <jonah.pal...@oracle.com> > > wrote: > >> > >> Add VIRTIO_F_IN_ORDER feature support for the virtqueue_fill operation. > >> > >> The goal of the virtqueue_ordered_fill operation when the > >> VIRTIO_F_IN_ORDER feature has been negotiated is to search for this > >> now-used element, set its length, and mark the element as filled in > >> the VirtQueue's used_elems array. > >> > >> By marking the element as filled, it will indicate that this element has > >> been processed and is ready to be flushed, so long as the element is > >> in-order. > >> > >> Signed-off-by: Jonah Palmer <jonah.pal...@oracle.com> > >> --- > >> hw/virtio/virtio.c | 36 +++++++++++++++++++++++++++++++++++- > >> 1 file changed, 35 insertions(+), 1 deletion(-) > >> > >> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > >> index 7456d61bc8..01b6b32460 100644 > >> --- a/hw/virtio/virtio.c > >> +++ b/hw/virtio/virtio.c > >> @@ -873,6 +873,38 @@ static void virtqueue_packed_fill(VirtQueue *vq, > >> const VirtQueueElement *elem, > >> vq->used_elems[idx].ndescs = elem->ndescs; > >> } > >> > >> +static void virtqueue_ordered_fill(VirtQueue *vq, const VirtQueueElement > >> *elem, > >> + unsigned int len) > >> +{ > >> + unsigned int i, steps, max_steps; > >> + > >> + i = vq->used_idx; > >> + steps = 0; > >> + /* > >> + * We shouldn't need to increase 'i' by more than the distance > >> + * between used_idx and last_avail_idx. > >> + */ > >> + max_steps = (vq->last_avail_idx + vq->vring.num - vq->used_idx) > >> + % vq->vring.num; > > > > I may be missing something, but (+vq->vring.num) is redundant if we (% > > vq->vring.num), isn't it? > > > > It ensures the result is always non-negative (e.g. when > vq->last_avail_idx < vq->used_idx). > > I wasn't sure how different platforms or compilers would handle > something like -5 % 10, so to be safe I included the '+ vq->vring.num'. > > For example, on my system, in test.c; > > #include <stdio.h> > > int main() { > unsigned int result = -5 % 10; > printf("Result of -5 %% 10 is: %d\n", result); > return 0; > } > > # gcc -o test test.c > > # ./test > Result of -5 % 10 is: -5 >
I think the modulo is being done in signed ints in your test, and then converting a signed int to an unsigned int. Like result = (-5 % 10). The unsigned wrap is always defined in C, and vq->last_avail_idx and vq->used_idx are both unsigned. Here is a closer test: int main(void) { unsigned int a = -5, b = 2; unsigned int result = (b-a) % 10; printf("Result of -5 %% 10 is: %u\n", result); return 0; } But it is a good catch for signed ints for sure :). Thanks! > >> + > >> + /* Search for element in vq->used_elems */ > >> + while (steps <= max_steps) { > >> + /* Found element, set length and mark as filled */ > >> + if (vq->used_elems[i].index == elem->index) { > >> + vq->used_elems[i].len = len; > >> + vq->used_elems[i].in_order_filled = true; > >> + break; > >> + } > >> + > >> + i += vq->used_elems[i].ndescs; > >> + steps += vq->used_elems[i].ndescs; > >> + > >> + if (i >= vq->vring.num) { > >> + i -= vq->vring.num; > >> + } > >> + } > >> +} > >> + > > > > Let's report an error if we finish the loop. I think: > > qemu_log_mask(LOG_GUEST_ERROR, > > "%s: %s cannot fill buffer id %u\n", > > __func__, vdev->name, elem->index); > > > > (or similar) should do. > > > > apart form that, > > > > Reviewed-by: Eugenio Pérez <epere...@redhat.com> > > > > Gotcha. Will add this in v3. > > Thank you Eugenio! > > >> static void virtqueue_packed_fill_desc(VirtQueue *vq, > >> const VirtQueueElement *elem, > >> unsigned int idx, > >> @@ -923,7 +955,9 @@ void virtqueue_fill(VirtQueue *vq, const > >> VirtQueueElement *elem, > >> return; > >> } > >> > >> - if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > >> + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_IN_ORDER)) { > >> + virtqueue_ordered_fill(vq, elem, len); > >> + } else if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > >> virtqueue_packed_fill(vq, elem, len, idx); > >> } else { > >> virtqueue_split_fill(vq, elem, len, idx); > >> -- > >> 2.39.3 > >> > > >