Introduce support for zero-copy BPF buffering, which reduces the

overhead of packet capture by allowing a user process to directly "loan"
buffer memory to the kernel rather than using read(2) to explicitly copy
data from kernel address space.

The user process will issue new BPF ioctls to set the shared memory
buffer mode and provide pointers to buffers and their size. The kernel
then wires and maps the pages into kernel address space using sf_buf(9),
which on supporting architectures will use the direct map region. The
current "buffered" access mode remains the default, and support for
zero-copy buffers must, for the time being, be explicitly enabled using
a sysctl for the kernel to accept requests to use it.

The kernel and user process synchronize use of the buffers with atomic
operations, avoiding the need for system calls under load; the user
process may use select()/poll()/kqueue() to manage blocking while
waiting for network data if the user process is able to consume data
faster than the kernel generates it. Patchs to libpcap are available
to allow libpcap applications to transparently take advantage of this
support. Detailed information on the new API may be found in bpf(4),
including specific atomic operations and memory barriers required to
synchronize buffer use safely.

These changes modify the base BPF implementation to (roughly) abstrac
the current buffer model, allowing the new shared memory model to be
added, and add new monitoring statistics for netstat to print. The
implementation, with the exception of some monitoring hanges that break
the netstat monitoring ABI for BPF, will be MFC'd.

Zerocopy bpf buffers are still considered experimental are disabled
by default. To experiment with this new facility, adjust the
net.bpf.zerocopy_enable sysctl variable to 1.

Changes to libpcap will be made available as a patch for the time being,
and further refinements to the implementation are expected.

Sponsored by:		Seccuris Inc.
In collaboration with:	rwatson
Tested by:		pwood, gallatin
MFC after:		4 months [1]

[1] Certain portions will probably not be MFCed, specifically things
    that can break the monitoring ABI.

1 files changed, 210 insertions, 0 deletions

diff --git a/sys/net/bpf_buffer.c b/sys/net/bpf_buffer.c
new file mode 100644
index 0000000..f07e948
--- /dev/null
+++ b/sys/net/bpf_buffer.c
@@ -0,0 +1,210 @@
+/*-
+ * Copyright (c) 2007 Seccuris Inc.
+ * All rights reserved.
+ *
+ * This sofware was developed by Robert N. M. Watson under contract to
+ * Seccuris Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * Copyright (c) 1990, 1991, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * This code is derived from the Stanford/CMU enet packet filter,
+ * (net/enet.c) distributed as part of 4.3BSD, and code contributed
+ * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence
+ * Berkeley Laboratory.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *      @(#)bpf.c	8.4 (Berkeley) 1/9/95
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include "opt_bpf.h"
+
+#include <sys/param.h>
+#include <sys/malloc.h>
+#include <sys/mbuf.h>
+#include <sys/socket.h>
+#include <sys/uio.h>
+#include <sys/kernel.h>
+#include <sys/sysctl.h>
+
+#include <net/if.h>
+#include <net/bpf.h>
+#include <net/bpf_buffer.h>
+#include <net/bpfdesc.h>
+
+/*
+ * Implement historical kernel memory buffering model for BPF: two malloc(9)
+ * kernel buffers are hung off of the descriptor.  The size is fixed prior to
+ * attaching to an ifnet, ad cannot be changed after that.  read(2) simply
+ * copies the data to user space using uiomove(9).
+ */
+
+static int bpf_bufsize = 4096;
+SYSCTL_INT(_net_bpf, OID_AUTO, bufsize, CTLFLAG_RW,
+    &bpf_bufsize, 0, "");
+static int bpf_maxbufsize = BPF_MAXBUFSIZE;
+SYSCTL_INT(_net_bpf, OID_AUTO, maxbufsize, CTLFLAG_RW,
+    &bpf_maxbufsize, 0, "");
+
+void
+bpf_buffer_alloc(struct bpf_d *d)
+{
+
+	KASSERT(d->bd_fbuf == NULL, ("bpf_buffer_alloc: bd_fbuf != NULL"));
+	KASSERT(d->bd_sbuf == NULL, ("bpf_buffer_alloc: bd_sbuf != NULL"));
+	KASSERT(d->bd_hbuf == NULL, ("bpf_buffer_alloc: bd_hbuf != NULL"));
+
+	d->bd_fbuf = (caddr_t)malloc(d->bd_bufsize, M_BPF, M_WAITOK);
+	d->bd_sbuf = (caddr_t)malloc(d->bd_bufsize, M_BPF, M_WAITOK);
+	d->bd_hbuf = NULL;
+	d->bd_slen = 0;
+	d->bd_hlen = 0;
+}
+
+/*
+ * Simple data copy to the current kernel buffer.
+ */
+void
+bpf_buffer_append_bytes(struct bpf_d *d, caddr_t buf, u_int offset,
+    void *src, u_int len)
+{
+	u_char *src_bytes;
+
+	src_bytes = (u_char *)src;
+	bcopy(src_bytes, buf + offset, len);
+}
+
+/*
+ * Scatter-gather data copy from an mbuf chain to the current kernel buffer.
+ */
+void
+bpf_buffer_append_mbuf(struct bpf_d *d, caddr_t buf, u_int offset, void *src,
+    u_int len)
+{
+	const struct mbuf *m;
+	u_char *dst;
+	u_int count;
+
+	m = (struct mbuf *)src;
+	dst = (u_char *)buf + offset;
+	while (len > 0) {
+		if (m == NULL)
+			panic("bpf_mcopy");
+		count = min(m->m_len, len);
+		bcopy(mtod(m, void *), dst, count);
+		m = m->m_next;
+		dst += count;
+		len -= count;
+	}
+}
+
+/*
+ * Free BPF kernel buffers on device close.
+ */
+void
+bpf_buffer_free(struct bpf_d *d)
+{
+
+	if (d->bd_sbuf != NULL)
+		free(d->bd_sbuf, M_BPF);
+	if (d->bd_hbuf != NULL)
+		free(d->bd_hbuf, M_BPF);
+	if (d->bd_fbuf != NULL)
+		free(d->bd_fbuf, M_BPF);
+
+#ifdef INVARIANTS
+	d->bd_sbuf = d->bd_hbuf = d->bd_fbuf = (caddr_t)~0;
+#endif
+}
+
+/*
+ * This is a historical initialization that occurs when the BPF descriptor is
+ * first opened.  It does not imply selection of a buffer mode, so we don't
+ * allocate buffers here.
+ */
+void
+bpf_buffer_init(struct bpf_d *d)
+{
+
+	d->bd_bufsize = bpf_bufsize;
+}
+
+/*
+ * Allocate or resize buffers.
+ */
+int
+bpf_buffer_ioctl_sblen(struct bpf_d *d, u_int *i)
+{
+	u_int size;
+
+	BPFD_LOCK(d);
+	if (d->bd_bif != NULL) {
+		BPFD_UNLOCK(d);
+		return (EINVAL);
+	}
+	size = *i;
+	if (size > bpf_maxbufsize)
+		*i = size = bpf_maxbufsize;
+	else if (size < BPF_MINBUFSIZE)
+		*i = size = BPF_MINBUFSIZE;
+	d->bd_bufsize = size;
+	BPFD_UNLOCK(d);
+	return (0);
+}
+
+/*
+ * Copy buffer storage to user space in read().
+ */
+int
+bpf_buffer_uiomove(struct bpf_d *d, caddr_t buf, u_int len, struct uio *uio)
+{
+
+	return (uiomove(buf, len, uio));
+}