Xen netback driver rewrite.

share/man/man4/Makefile,
share/man/man4/xnb.4,
sys/dev/xen/netback/netback.c,
sys/dev/xen/netback/netback_unit_tests.c:

	Rewrote the netback driver for xen to attach properly via newbus
	and work properly in both HVM and PVM mode (only HVM is tested).
	Works with the in-tree FreeBSD netfront driver or the Windows
	netfront driver from SuSE.  Has not been extensively tested with
	a Linux netfront driver.  Does not implement LRO, TSO, or
	polling.  Includes unit tests that may be run through sysctl
	after compiling with XNB_DEBUG defined.

sys/dev/xen/blkback/blkback.c,
sys/xen/interface/io/netif.h:

	Comment elaboration.

sys/kern/uipc_mbuf.c:

	Fix page fault in kernel mode when calling m_print() on a
	null mbuf.  Since m_print() is only used for debugging, there
	are no performance concerns for extra error checking code.

sys/kern/subr_scanf.c:

	Add the "hh" and "ll" width specifiers from C99 to scanf().
	A few callers were already using "ll" even though scanf()
	was handling it as "l".

Submitted by:	Alan Somers <alans@spectralogic.com>
Submitted by:	John Suykerbuyk <johns@spectralogic.com>
Sponsored by:	Spectra Logic
MFC after:	1 week
Reviewed by:	ken

2 files changed, 136 insertions, 0 deletions

diff --git a/share/man/man4/Makefile b/share/man/man4/Makefile
index e935472..90dcdeb 100644
--- a/share/man/man4/Makefile
+++ b/share/man/man4/Makefile
@@ -531,6 +531,7 @@ MAN=	aac.4 \
 	${_xen.4} \
 	xhci.4 \
 	xl.4 \
+	${_xnb.4} \
 	xpt.4 \
 	zero.4 \
 	zyd.4
@@ -731,6 +732,7 @@ _urtw.4=	urtw.4
 _viawd.4=	viawd.4
 _wpi.4=		wpi.4
 _xen.4=		xen.4
+_xnb.4=		xnb.4
 
 MLINKS+=lindev.4 full.4
 .endif
diff --git a/share/man/man4/xnb.4 b/share/man/man4/xnb.4
new file mode 100644
index 0000000..f2d8f8a
--- /dev/null
+++ b/share/man/man4/xnb.4
@@ -0,0 +1,134 @@
+.\" Copyright (c) 2012 Spectra Logic Corporation
+.\"	All rights reserved.
+.\"
+.\"
+.\" 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,
+.\"    without modification.
+.\" 2. Redistributions in binary form must reproduce at minimum a disclaimer
+.\"    substantially similar to the "NO WARRANTY" disclaimer below
+.\"    ("Disclaimer") and any redistribution must be conditioned upon
+.\"    including a substantially similar Disclaimer requirement for further
+.\"    binary redistribution.
+.\" 
+.\" NO WARRANTY
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
+.\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+.\" HOLDERS OR CONTRIBUTORS BE LIABLE FOR 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 DAMAGES.
+.\" 
+.\" Authors: Alan Somers         (Spectra Logic Corporation)
+.\" 
+.\" $FreeBSD$
+.\"
+
+.Dd January 6, 2012
+.Dt XNB 4
+.Os 
+.Sh NAME
+.Nm xnb
+.Nd "Xen Paravirtualized Backend Ethernet Driver"
+.Sh SYNOPSIS
+To compile this driver into the kernel, place the following lines in your
+kernel configuration file:
+.Bd -ragged -offset indent
+.Cd "options XENHVM"
+.Cd "device xenpci"
+.Ed
+.Sh DESCRIPTION
+The
+.Nm
+driver provides the back half of a paravirtualized
+.Xr xen 4
+network connection.  The netback and netfront drivers appear to their
+respective operating systems as Ethernet devices linked by a crossover cable.
+Typically,
+.Nm
+will run on Domain 0 and the netfront driver will run on a guest domain.
+However, it is also possible to run
+.Nm
+on a guest domain.  It may be bridged or routed to provide the netfront's
+domain access to other guest domains or to a physical network.
+.Pp
+In most respects, the
+.Nm
+device appears to the OS as an other Ethernet device.  It can be configured at
+runtime entirely with
+.Xr ifconfig 8
+\&.  In particular, it supports MAC changing, arbitrary MTU sizes, checksum
+offload for IP, UDP, and TCP for both receive and transmit, and TSO.  However,
+see
+.Sx CAVEATS
+before enabling txcsum, rxcsum, or tso.
+.Sh SYSCTL VARIABLES
+The following read-only variables are available via
+.Xr sysctl 8 :
+.Bl -tag -width indent
+.It Va dev.xnb.%d.dump_rings
+Displays information about the ring buffers used to pass requests between the
+netfront and netback.  Mostly useful for debugging, but can also be used to
+get traffic statistics.
+.It Va dev.xnb.%d.unit_test_results
+Runs a builtin suite of unit tests and displays the results.  Does not affect
+the operation of the driver in any way.  Note that the test suite simulates
+error conditions; this will result in error messages being printed to the
+system system log.
+.Sh CAVEATS
+Packets sent through Xennet pass over shared memory, so the protocol includes
+no form of link-layer checksum or CRC.  Furthermore, Xennet drivers always
+report to their hosts that they support receive and transmit checksum
+offloading.  They "offload" the checksum calculation by simply skipping it.
+That works fine for packets that are exchanged between two domains on the same
+machine.  However, when a Xennet interface is bridged to a physical interface,
+a correct checksum must be attached to any packets bound for that physical
+interface.  Currently, FreeBSD lacks any mechanism for an ethernet device to
+inform the OS that newly received packets are valid even though their checksums
+are not.  So if the netfront driver is configured to offload checksum
+calculations, it will pass non-checksumed packets to
+.Nm
+, which must then calculate the checksum in software before passing the packet
+to the OS.
+.Pp
+For this reason, it is recommended that if
+.Nm
+is bridged to a physcal interface, then transmit checksum offloading should be
+disabled on the netfront.  The Xennet protocol does not have any mechanism for
+the netback to request the netfront to do this; the operator must do it
+manually.
+.Sh SEE ALSO
+.Xr arp 4 ,
+.Xr netintro 4 ,
+.Xr ng_ether 4 ,
+.Xr ifconfig 8 ,
+.Xr xen 4
+.Sh HISTORY
+The
+.Nm
+device driver first appeared in
+.Fx 10.0
+.
+.Sh AUTHORS
+The
+.Nm
+driver was written by
+.An Alan Somers
+.Aq alans@spectralogic.com
+and
+.An John Suykerbuyk
+.Aq johns@spectralogic.com
+.Sh BUGS
+The
+.Nm
+driver does not properly checksum UDP datagrams that span more than one
+Ethernet frame.  Nor does it correctly checksum IPv6 packets.  To workaround
+that bug, disable transmit checksum offloading on the netfront driver.