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, 50 insertions, 0 deletions

diff --git a/sys/net/bpf_buffer.h b/sys/net/bpf_buffer.h
new file mode 100644
index 0000000..82d0310
--- /dev/null
+++ b/sys/net/bpf_buffer.h
@@ -0,0 +1,50 @@
+/*-
+ * 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.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef _NET_BPF_BUFFER_H_
+#define	_NET_BPF_BUFFER_H_
+
+#ifndef _KERNEL
+#error "no user-serviceable parts inside"
+#endif
+
+void	bpf_buffer_alloc(struct bpf_d *d);
+void	bpf_buffer_append_bytes(struct bpf_d *d, caddr_t buf, u_int offset,
+	    void *src, u_int len);
+void	bpf_buffer_append_mbuf(struct bpf_d *d, caddr_t buf, u_int offset,
+	    void *src, u_int len);
+void	bpf_buffer_free(struct bpf_d *d);
+void	bpf_buffer_init(struct bpf_d *d);
+int	bpf_buffer_ioctl_sblen(struct bpf_d *d, u_int *i);
+int	bpf_buffer_uiomove(struct bpf_d *d, caddr_t buf, u_int len,
+	    struct uio *uio);
+
+#endif /* !_NET_BPF_BUFFER_H_ */