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netmap: if_vtnet: avoid netmap ring wraparound

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netmap assumes the one "slot" is left unused to distinguish
the empty ring and full ring conditions. This assumption was
violated by vtnet_netmap_rxq_populate().

MFC after:	1 week
This commit is contained in:
Vincenzo Maffione 2020-06-01 16:14:29 +00:00
parent 36f2d67026
commit 9ec71596c0
1 changed files with 2 additions and 2 deletions
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4
sys/dev/netmap/if_vtnet_netmap.h
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@ -275,8 +275,8 @@ vtnet_netmap_rxq_populate(struct vtnet_rxq *rxq)
/* Expose all the RX netmap buffers we can. In case of no indirect
* buffers, the number of netmap slots in the RX ring matches the
* maximum number of 2-elements sglist that the RX virtqueue can
* accommodate. */
error = vtnet_netmap_kring_refill(kring, na->num_rx_desc);
* accommodate (minus 1 to avoid netmap ring wraparound). */
error = vtnet_netmap_kring_refill(kring, na->num_rx_desc - 1);
virtqueue_notify(rxq->vtnrx_vq);
return error < 0 ? ENXIO : 0;