1 .\" Copyright (c) 2012 Spectra Logic Corporation
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions, and the following disclaimer,
9 .\" without modification.
10 .\" 2. Redistributions in binary form must reproduce at minimum a disclaimer
11 .\" substantially similar to the "NO WARRANTY" disclaimer below
12 .\" ("Disclaimer") and any redistribution must be conditioned upon
13 .\" including a substantially similar Disclaimer requirement for further
14 .\" binary redistribution.
17 .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
18 .\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
19 .\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
20 .\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
21 .\" HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
25 .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
26 .\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27 .\" POSSIBILITY OF SUCH DAMAGES.
29 .\" Authors: Alan Somers (Spectra Logic Corporation)
36 .Nd "Xen Paravirtualized Backend Ethernet Driver"
38 To compile this driver into the kernel, place the following lines in your
39 kernel configuration file:
40 .Bd -ragged -offset indent
47 driver provides the back half of a paravirtualized
50 The netback and netfront drivers appear to their respective operating
51 systems as Ethernet devices linked by a crossover cable.
54 will run on Domain 0 and the netfront driver will run on a guest domain.
55 However, it is also possible to run
58 It may be bridged or routed to provide the netfront
59 domain access to other guest domains or to a physical network.
63 device appears to the OS as any other Ethernet device.
64 It can be configured at runtime entirely with
66 In particular, it supports MAC changing, arbitrary MTU sizes, checksum
67 offload for IP, UDP, and TCP for both receive and transmit, and TSO.
70 before enabling txcsum, rxcsum, or tso.
72 The following read-only variables are available via
74 .Bl -tag -width indent
75 .It Va dev.xnb.%d.dump_rings
76 Displays information about the ring buffers used to pass requests between the
78 Mostly useful for debugging, but can also be used to
79 get traffic statistics.
80 .It Va dev.xnb.%d.unit_test_results
81 Runs a builtin suite of unit tests and displays the results.
82 Does not affect the operation of the driver in any way.
83 Note that the test suite simulates error conditions; this will result in
84 error messages being printed to the system log.
95 device driver first appeared in
101 driver was written by
102 .An Alan Somers Aq Mt asomers@FreeBSD.org
105 Packets sent through Xennet pass over shared memory, so the protocol includes
106 no form of link-layer checksum or CRC.
107 Furthermore, Xennet drivers always report to their hosts that they support
108 receive and transmit checksum offloading.
109 They "offload" the checksum calculation by simply skipping it.
110 That works fine for packets that are exchanged between two domains on the same
112 However, when a Xennet interface is bridged to a physical interface,
113 a correct checksum must be attached to any packets bound for that physical
117 lacks any mechanism for an Ethernet device to
118 inform the OS that newly received packets are valid even though their checksums
120 So if the netfront driver is configured to offload checksum calculations,
121 it will pass non-checksumed packets to
123 which must then calculate the checksum in software before passing the packet
126 For this reason, it is recommended that if
128 is bridged to a physical interface, then transmit checksum offloading should be
129 disabled on the netfront.
130 The Xennet protocol does not have any mechanism for the netback to request
131 the netfront to do this; the operator must do it manually.
135 driver does not properly checksum UDP datagrams that span more than one
137 Nor does it correctly checksum IPv6 packets.
138 To workaround that bug, disable transmit checksum offloading on the