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diff --git a/sys/dev/netmap/netmap_freebsd.c b/sys/dev/netmap/netmap_freebsd.c
--- a/sys/dev/netmap/netmap_freebsd.c
+++ b/sys/dev/netmap/netmap_freebsd.c
@@ -405,15 +405,20 @@
* addr and len identify the netmap buffer, m is the (preallocated)
* mbuf to use for transmissions.
*
- * We should add a reference to the mbuf so the m_freem() at the end
- * of the transmission does not consume resources.
+ * Zero-copy transmission is possible if netmap is attached directly to a
+ * hardware interface: when cleaning we simply wait for the mbuf cluster
+ * refcount to decrement to 1, indicating that the driver has completed
+ * transmission and is done with the buffer. However, this approach can
+ * lead to queue deadlocks when attaching to software interfaces (e.g.,
+ * if_bridge) since we cannot rely on member ports to promptly reclaim
+ * transmitted mbufs. Since there is no easy way to distinguish these
+ * cases, we currently always copy the buffer.
*
- * On FreeBSD, and on multiqueue cards, we can force the queue using
+ * On multiqueue cards, we can force the queue using
* if (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE)
* i = m->m_pkthdr.flowid % adapter->num_queues;
* else
* i = curcpu % adapter->num_queues;
- *
*/
int
nm_os_generic_xmit_frame(struct nm_os_gen_arg *a)
@@ -423,16 +428,18 @@
struct ifnet *ifp = a->ifp;
struct mbuf *m = a->m;
- /* Link the external storage to
- * the netmap buffer, so that no copy is necessary. */
- m->m_ext.ext_buf = m->m_data = a->addr;
- m->m_ext.ext_size = len;
+ if (MBUF_REFCNT(m) != 1) {
+ nm_prerr("invalid refcnt %d for %p", MBUF_REFCNT(m), m);
+ panic("in generic_xmit_frame");
+ }
+ if (unlikely(m->m_ext.ext_size < len)) {
+ nm_prlim(2, "size %d < len %d", m->m_ext.ext_size, len);
+ len = m->m_ext.ext_size;
+ }
+ memcpy(m->m_data, a->addr, len);
m->m_flags |= M_PKTHDR;
m->m_len = m->m_pkthdr.len = len;
-
- /* mbuf refcnt is not contended, no need to use atomic
- * (a memory barrier is enough). */
SET_MBUF_REFCNT(m, 2);
M_HASHTYPE_SET(m, M_HASHTYPE_OPAQUE);
m->m_pkthdr.flowid = a->ring_nr;
@@ -443,7 +450,6 @@
return ret ? -1 : 0;
}
-
struct netmap_adapter *
netmap_getna(if_t ifp)
{
diff --git a/sys/dev/netmap/netmap_generic.c b/sys/dev/netmap/netmap_generic.c
--- a/sys/dev/netmap/netmap_generic.c
+++ b/sys/dev/netmap/netmap_generic.c
@@ -537,10 +537,12 @@
}
/* The event has been consumed, we can go
* ahead. */
-
} else if (MBUF_REFCNT(m) != 1) {
- /* This mbuf is still busy: its refcnt is 2. */
- break;
+ /* This mbuf has been submitted but is still busy
+ * (refcount is 2).
+ * Leave it to the driver and replenish. */
+ m_freem(m);
+ tx_pool[nm_i] = NULL;
}
}
@@ -631,10 +633,8 @@
/* Decrement the refcount. This will free it if we lose the race
* with the driver. */
m_freem(m);
- smp_mb();
}
-
/*
* generic_netmap_txsync() transforms netmap buffers into mbufs
* and passes them to the standard device driver
@@ -698,7 +698,7 @@
/* Tale a mbuf from the tx pool (replenishing the pool
* entry if necessary) and copy in the user packet. */
m = kring->tx_pool[nm_i];
- if (unlikely(m == NULL)) {
+ if (m == NULL) {
kring->tx_pool[nm_i] = m =
nm_os_get_mbuf(ifp, NETMAP_BUF_SIZE(na));
if (m == NULL) {
diff --git a/sys/dev/netmap/netmap_kern.h b/sys/dev/netmap/netmap_kern.h
--- a/sys/dev/netmap/netmap_kern.h
+++ b/sys/dev/netmap/netmap_kern.h
@@ -2394,7 +2394,7 @@
* has a KASSERT(), checking that the mbuf dtor function is not NULL.
*/
-static void void_mbuf_dtor(struct mbuf *m) { }
+static inline void void_mbuf_dtor(struct mbuf *m) { }
#define SET_MBUF_DESTRUCTOR(m, fn) do { \
(m)->m_ext.ext_free = (fn != NULL) ? \
@@ -2402,22 +2402,9 @@
} while (0)
static inline struct mbuf *
-nm_os_get_mbuf(struct ifnet *ifp, int len)
+nm_os_get_mbuf(struct ifnet *ifp __unused, int len)
{
- struct mbuf *m;
-
- (void)ifp;
- (void)len;
-
- m = m_gethdr(M_NOWAIT, MT_DATA);
- if (m == NULL) {
- return m;
- }
-
- m_extadd(m, NULL /* buf */, 0 /* size */, void_mbuf_dtor,
- NULL, NULL, 0, EXT_NET_DRV);
-
- return m;
+ return (m_getjcl(M_NOWAIT, MT_DATA, M_PKTHDR, len));
}
#endif /* __FreeBSD__ */

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