On 2018年04月25日 13:15, Tiwei Bie wrote:
+ /* We're using some buffers from the free list. */
+ vq->vq.num_free -= descs_used;
+
+ /* Update free pointer */
+ if (indirect) {
+ n = head + 1;
+ if (n >= vq->vring_packed.num) {
+ n = 0;
+ vq->wrap_counter ^= 1;
+ }
+ vq->next_avail_idx = n;
+ } else
+ vq->next_avail_idx = i;
During testing zerocopy (out of order completion), I found driver may
submit two identical buffer id to vhost. So the above code may not work
well.
Consider the case that driver adds 3 buffer and virtqueue size is 8.
a) id = 0,count = 2,next_avail = 2
b) id = 2,count = 4,next_avail = 2
c) id = 4,count = 2,next_avail = 0
if packet b is done before packet a, driver may think buffer id 0 is
available and try to use it if even if the real buffer 0 was not done.
Thanks
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