change netmap global lock to sx?

[Navdeep Parhar]

I'd like to change the netmap global lock from a mutex into a sleepable
shared/exclusive lock.  This will allow a driver's nm_register hook
(which is called with the global lock held) to sleep if it has to.  I've
casually used pkt-gen after this conversion (patch attached) and the
witness hasn't complained about it.

Thoughts?

Regards,
Navdeep


diff -r 0300d80260f4 sys/dev/netmap/netmap_kern.h
--- a/sys/dev/netmap/netmap_kern.h	Fri May 23 19:00:56 2014 -0700
+++ b/sys/dev/netmap/netmap_kern.h	Sat May 24 12:49:15 2014 -0700
@@ -43,13 +43,13 @@
 #define unlikely(x)	__builtin_expect((long)!!(x), 0L)

 #define	NM_LOCK_T	struct mtx
-#define	NMG_LOCK_T	struct mtx
-#define NMG_LOCK_INIT()	mtx_init(&netmap_global_lock, \
-				"netmap global lock", NULL, MTX_DEF)
-#define NMG_LOCK_DESTROY()	mtx_destroy(&netmap_global_lock)
-#define NMG_LOCK()	mtx_lock(&netmap_global_lock)
-#define NMG_UNLOCK()	mtx_unlock(&netmap_global_lock)
-#define NMG_LOCK_ASSERT()	mtx_assert(&netmap_global_lock, MA_OWNED)
+#define	NMG_LOCK_T	struct sx
+#define NMG_LOCK_INIT()	sx_init(&netmap_global_lock, \
+				"netmap global lock")
+#define NMG_LOCK_DESTROY()	sx_destroy(&netmap_global_lock)
+#define NMG_LOCK()	sx_xlock(&netmap_global_lock)
+#define NMG_UNLOCK()	sx_xunlock(&netmap_global_lock)
+#define NMG_LOCK_ASSERT()	sx_assert(&netmap_global_lock, SA_XLOCKED)

 #define	NM_SELINFO_T	struct selinfo
 #define	MBUF_LEN(m)	((m)->m_pkthdr.len)