PERFORCE change 131531 for review

[Robert Watson]

http://perforce.freebsd.org/chv.cgi?CH=131531

Change 131531 by rwatson at rwatson_cinnamon on 2007/12/24 17:58:48

	First cut at improving behavior of zero-copy BPF buffers on
	systems with weaker memory ordering with i386.  In certain
	cases, it will also help consistency on i386.
	
	Suggested by:	jhb

Affected files ...

.. //depot/projects/zcopybpf/src/contrib/libpcap/pcap-bpf.c#15 edit
.. //depot/projects/zcopybpf/src/sys/net/bpf_zerocopy.c#25 edit

Differences ...

==== //depot/projects/zcopybpf/src/contrib/libpcap/pcap-bpf.c#15 (text+ko) ====

@@ -39,6 +39,10 @@
 #include <sys/ioctl.h>
 #include <sys/utsname.h>
 
+#ifdef BIOCGETBUFMODE
+#include <machine/atomic.h>
+#endif
+
 #include <net/if.h>
 
 #ifdef _AIX
@@ -160,7 +164,8 @@
 	 */
 	if (p->zbuffer == p->zbuf2 || p->zbuffer == NULL) {
 		bzh = (struct bpf_zbuf_header *)p->zbuf1;
-		if (bzh->bzh_kernel_gen != bzh->bzh_user_gen) {
+		if (bzh->bzh_user_gen !=
+		    atomic_load_acq_int(&bzh->bzh_kernel_gen)) {
 			p->bzh = bzh;
 			p->zbuffer = (u_char *)p->zbuf1;
 			p->buffer = p->zbuffer + sizeof(*bzh);
@@ -169,7 +174,8 @@
 		}
 	} else if (p->zbuffer == p->zbuf1) {
 		bzh = (struct bpf_zbuf_header *)p->zbuf2;
-		if (bzh->bzh_kernel_gen != bzh->bzh_user_gen) {
+		if (bzh->bzh_user_gen !=
+		    atomic_load_acq_int(&bzh->bzh_kernel_gen)) {
 			p->bzh = bzh;
 			p->zbuffer = (u_char *)p->zbuf2;
 			p->buffer = p->zbuffer + sizeof(*bzh);
@@ -249,9 +255,8 @@
 static int
 pcap_ack_zbuf(pcap_t *p)
 {
-	struct bpf_zbuf bz;
 
-	p->bzh->bzh_user_gen = p->bzh->bzh_kernel_gen;
+	atomic_store_rel_int(&p->bzh->bzh_user_gen, p->bzh->bzh_kernel_gen);
 	p->bzh = NULL;
 	p->buffer = NULL;
 	return (0);

==== //depot/projects/zcopybpf/src/sys/net/bpf_zerocopy.c#25 (text+ko) ====

@@ -42,6 +42,8 @@
 #include <sys/socket.h>
 #include <sys/uio.h>
 
+#include <machine/atomic.h>
+
 #include <net/if.h>
 #include <net/bpf.h>
 #include <net/bpfdesc.h>
@@ -354,7 +356,7 @@
 	zb = (struct zbuf *)d->bd_hbuf;
 	KASSERT(zb != NULL, ("bpf_zerocopy_bufheld: zb == NULL"));
 	zb->zb_header->bzh_kernel_len = d->bd_hlen;
-	zb->zb_header->bzh_kernel_gen++;
+	atomic_add_rel_int(&zb->zb_header->bzh_kernel_gen, 1);
 }
 
 /*
@@ -376,7 +378,8 @@
 	zb = (struct zbuf *)d->bd_hbuf;
 	if (zb == NULL)
 		return (0);
-	if (zb->zb_header->bzh_kernel_gen == zb->zb_header->bzh_user_gen)
+	if (zb->zb_header->bzh_kernel_gen ==
+	    atomic_load_acq_int(&zb->zb_header->bzh_user_gen))
 		return (1);
 	return (0);
 }