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authorgrehan <grehan@FreeBSD.org>2013-03-06 07:28:20 +0000
committergrehan <grehan@FreeBSD.org>2013-03-06 07:28:20 +0000
commit2527cbb869d02606cbf9bf5a54d79a5246920bca (patch)
tree5c821ef513a52f4120229c192ce73c4a9e73d99c /usr.sbin
parent840f21fc4922b144ba355c33e2fbab7970d7a18f (diff)
downloadFreeBSD-src-2527cbb869d02606cbf9bf5a54d79a5246920bca.zip
FreeBSD-src-2527cbb869d02606cbf9bf5a54d79a5246920bca.tar.gz
Simplify virtio ring num-available calculation.
Submitted by: Chris Torek, torek at torek dot net
Diffstat (limited to 'usr.sbin')
-rw-r--r--usr.sbin/bhyve/pci_virtio_block.c17
-rw-r--r--usr.sbin/bhyve/pci_virtio_net.c15
2 files changed, 21 insertions, 11 deletions
diff --git a/usr.sbin/bhyve/pci_virtio_block.c b/usr.sbin/bhyve/pci_virtio_block.c
index 31ff2e6..0c34666 100644
--- a/usr.sbin/bhyve/pci_virtio_block.c
+++ b/usr.sbin/bhyve/pci_virtio_block.c
@@ -164,14 +164,19 @@ pci_vtblk_iosize(struct pci_devinst *pi)
static int
hq_num_avail(struct vring_hqueue *hq)
{
- int ndesc;
+ uint16_t ndesc;
- if (*hq->hq_avail_idx >= hq->hq_cur_aidx)
- ndesc = *hq->hq_avail_idx - hq->hq_cur_aidx;
- else
- ndesc = UINT16_MAX - hq->hq_cur_aidx + *hq->hq_avail_idx + 1;
+ /*
+ * We're just computing (a-b) in GF(216).
+ *
+ * The only glitch here is that in standard C,
+ * uint16_t promotes to (signed) int when int has
+ * more than 16 bits (pretty much always now), so
+ * we have to force it back to unsigned.
+ */
+ ndesc = (unsigned)*hq->hq_avail_idx - (unsigned)hq->hq_cur_aidx;
- assert(ndesc >= 0 && ndesc <= hq->hq_size);
+ assert(ndesc <= hq->hq_size);
return (ndesc);
}
diff --git a/usr.sbin/bhyve/pci_virtio_net.c b/usr.sbin/bhyve/pci_virtio_net.c
index a5cf8b3..11647d6 100644
--- a/usr.sbin/bhyve/pci_virtio_net.c
+++ b/usr.sbin/bhyve/pci_virtio_net.c
@@ -172,12 +172,17 @@ hq_num_avail(struct vring_hqueue *hq)
{
int ndesc;
- if (*hq->hq_avail_idx >= hq->hq_cur_aidx)
- ndesc = *hq->hq_avail_idx - hq->hq_cur_aidx;
- else
- ndesc = UINT16_MAX - hq->hq_cur_aidx + *hq->hq_avail_idx + 1;
+ /*
+ * We're just computing (a-b) in GF(216).
+ *
+ * The only glitch here is that in standard C,
+ * uint16_t promotes to (signed) int when int has
+ * more than 16 bits (pretty much always now), so
+ * we have to force it back to unsigned.
+ */
+ ndesc = (unsigned)*hq->hq_avail_idx - (unsigned)hq->hq_cur_aidx;
- assert(ndesc >= 0 && ndesc <= hq->hq_size);
+ assert(ndesc <= hq->hq_size);
return (ndesc);
}
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