.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
+.\"
+.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
.\" Permission is granted to distribute possibly modified copies
.\" of this page provided the header is included verbatim,
.\" and in case of nontrivial modification author and date
.\" of the modification is added to the header.
+.\" %%%LICENSE_END
+.\"
.\" $Id: packet.7,v 1.13 2000/08/14 08:03:45 ak Exp $
-.TH PACKET 7 2012-05-10 "Linux" "Linux Programmer's Manual"
+.\"
+.TH PACKET 7 2014-04-28 "Linux" "Linux Programmer's Manual"
.SH NAME
-packet \- packet interface on device level.
+packet \- packet interface on device level
.SH SYNOPSIS
.nf
.B #include <sys/socket.h>
.I socket_type
is either
.B SOCK_RAW
-for raw packets including the link level header or
+for raw packets including the link-level header or
.B SOCK_DGRAM
-for cooked packets with the link level header removed.
-The link level
-header information is available in a common format in a
+for cooked packets with the link-level header removed.
+The link-level header information is available in a common format in a
.IR sockaddr_ll .
.I protocol
-is the IEEE 802.3 protocol number in network order.
+is the IEEE 802.3 protocol number in network byte order.
See the
.I <linux/if_ether.h>
include file for a list of allowed protocols.
By default all packets of the specified protocol type
are passed to a packet socket.
-To only get packets from a specific interface use
+To get packets only from a specific interface use
.BR bind (2)
specifying an address in a
.I struct sockaddr_ll
.BR recvfrom (2)
the real length of the packet on the wire is always returned,
even when it is longer than the buffer.
-.SS Address Types
-The sockaddr_ll is a device independent physical layer address.
+.SS Address types
+The
+.I sockaddr_ll
+is a device independent physical layer address.
.in +4n
.nf
.in
.I sll_protocol
-is the standard ethernet protocol type in network order as defined
+is the standard ethernet protocol type in network byte order as defined
in the
.I <linux/if_ether.h>
include file.
.B PACKET_OUTGOING
for a packet originated from the local host that is looped back to a packet
socket.
-These types make only sense for receiving.
+These types make sense only for receiving.
.I sll_addr
and
.I sll_halen
and
.I sll_ifindex
are used.
-.SS Socket Options
+.SS Socket options
+Packet socket options are configured by calling
+.BR setsockopt (2)
+with level
+.BR SOL_PACKET .
+.TP
+.BR PACKET_ADD_MEMBERSHIP
+.PD 0
+.TP
+.BR PACKET_DROP_MEMBERSHIP
+.PD
Packet sockets can be used to configure physical layer multicasting
and promiscuous mode.
-It works by calling
-.BR setsockopt (2)
-on a packet socket for
-.B SOL_PACKET
-and one of the options
.B PACKET_ADD_MEMBERSHIP
-to add a binding or
+adds a binding and
.B PACKET_DROP_MEMBERSHIP
-to drop it.
+drops it.
They both expect a
-.B packet_mreq
+.I packet_mreq
structure as argument:
.in +4n
sets the socket up to receive all multicast packets arriving at
the interface.
-In addition the traditional ioctls
+In addition, the traditional ioctls
.BR SIOCSIFFLAGS ,
.BR SIOCADDMULTI ,
.B SIOCDELMULTI
can be used for the same purpose.
+.TP
+.BR PACKET_AUXDATA " (since Linux 2.6.21)"
+.\" commit 8dc4194474159660d7f37c495e3fc3f10d0db8cc
+If this binary option is enabled, the packet socket passes a metadata
+structure along with each packet in the
+.BR recvmsg (2)
+control field.
+The structure can be read with
+.BR cmsg (3).
+It is defined as
+
+.in +4n
+.nf
+struct tpacket_auxdata {
+ __u32 tp_status;
+ __u32 tp_len; /* packet length */
+ __u32 tp_snaplen; /* captured length */
+ __u16 tp_mac;
+ __u16 tp_net;
+ __u16 tp_vlan_tci;
+ __u16 tp_padding;
+};
+.fi
+.in
+.TP
+.BR PACKET_FANOUT " (since Linux 3.1)"
+.\" commit dc99f600698dcac69b8f56dda9a8a00d645c5ffc
+To scale processing across threads, packet sockets can form a fanout
+group.
+In this mode, each matching packet is enqueued onto only one
+socket in the group.
+A socket joins a fanout group by calling
+.BR setsockopt (2)
+with level
+.B SOL_PACKET
+and option
+.BR PACKET_FANOUT .
+Each network namespace can have up to 65536 independent groups.
+A socket selects a group by encoding the ID in the first 16 bits of
+the integer option value.
+The first packet socket to join a group implicitly creates it.
+To successfully join an existing group, subsequent packet sockets
+must have the same protocol, device settings, fanout mode and
+flags (see below).
+Packet sockets can leave a fanout group only by closing the socket.
+The group is deleted when the last socket is closed.
+
+Fanout supports multiple algorithms to spread traffic between sockets.
+The default mode,
+.BR PACKET_FANOUT_HASH ,
+sends packets from the same flow to the same socket to maintain
+per-flow ordering.
+For each packet, it chooses a socket by taking the packet flow hash
+modulo the number of sockets in the group, where a flow hash is a hash
+over network-layer address and optional transport-layer port fields.
+The load-balance mode
+.BR PACKET_FANOUT_LB
+implements a round-robin algorithm.
+.BR PACKET_FANOUT_CPU
+selects the socket based on the CPU that the packet arrived on.
+.BR PACKET_FANOUT_ROLLOVER
+processes all data on a single socket, moves to the next when one
+becomes backlogged.
+.BR PACKET_FANOUT_RND
+selects the socket using a pseudo-random number generator.
+.BR PACKET_FANOUT_QM
+.\" commit 2d36097d26b5991d71a2cf4a20c1a158f0f1bfcd
+(available since Linux 3.14)
+selects the socket using the recorded queue_mapping of the received skb.
+
+Fanout modes can take additional options.
+IP fragmentation causes packets from the same flow to have different
+flow hashes.
+The flag
+.BR PACKET_FANOUT_FLAG_DEFRAG ,
+if set, causes packet to be defragmented before fanout is applied, to
+preserve order even in this case.
+Fanout mode and options are communicated in the second 16 bits of the
+integer option value.
+The flag
+.BR PACKET_FANOUT_FLAG_ROLLOVER
+enables the roll over mechanism as a backup strategy: if the
+original fanout algorithm selects a backlogged socket, the packet
+rolls over to the next available one.
+.TP
+.BR PACKET_LOSS " (with " PACKET_TX_RING )
+When a malformed packet is encountered on a transmit ring,
+the default is to reset its
+.I tp_status
+to
+.BR TP_STATUS_WRONG_FORMAT
+and abort the transmission immediately.
+The malformed packet blocks itself and subsequently enqueued packets from
+being sent.
+The format error must be fixed, the associated
+.I tp_status
+reset to
+.BR TP_STATUS_SEND_REQUEST ,
+and the transmission process restarted via
+.BR send (2).
+However, if
+.BR PACKET_LOSS
+is set, any malformed packet will be skipped, its
+.I tp_status
+reset to
+.BR TP_STATUS_AVAILABLE ,
+and the transmission process continued.
+.TP
+.BR PACKET_RESERVE " (with " PACKET_RX_RING )
+By default, a packet receive ring writes packets immediately following the
+metadata structure and alignment padding.
+This integer option reserves additional headroom.
+.TP
+.BR PACKET_RX_RING
+Create a memory-mapped ring buffer for asynchronous packet reception.
+The packet socket reserves a contiguous region of application address
+space, lays it out into an array of packet slots and copies packets
+(up to
+.IR tp_snaplen )
+into subsequent slots.
+Each packet is preceded by a metadata structure similar to
+.IR tpacket_auxdata .
+The protocol fields encode the offset to the data
+from the start of the metadata header.
+.I tp_net
+stores the offset to the network layer.
+If the packet socket is of type
+.BR SOCK_DGRAM ,
+then
+.I tp_mac
+is the same.
+If it is of type
+.BR SOCK_RAW ,
+then that field stores the offset to the link-layer frame.
+Packet socket and application communicate the head and tail of the ring
+through the
+.I tp_status
+field.
+The packet socket owns all slots with
+.I tp_status
+equal to
+.BR TP_STATUS_KERNEL .
+After filling a slot, it changes the status of the slot to transfer
+ownership to the application.
+During normal operation, the new
+.I tp_status
+value has at least the
+.BR TP_STATUS_USER
+bit set to signal that a received packet has been stored.
+When the application has finished processing a packet, it transfers
+ownership of the slot back to the socket by setting
+.I tp_status
+equal to
+.BR TP_STATUS_KERNEL .
+Packet sockets implement multiple variants of the packet ring.
+The implementation details are described in
+.IR Documentation/networking/packet_mmap.txt
+in the Linux kernel source tree.
+.TP
+.BR PACKET_STATISTICS
+Retrieve packet socket statistics in the form of a structure
+
+.in +4n
+.nf
+struct tpacket_stats {
+ unsigned int tp_packets; /* Total packet count */
+ unsigned int tp_drops; /* Dropped packet count */
+};
+.fi
+.in
+
+Receiving statistics resets the internal counters.
+The statistics structure differs when using a ring of variant
+.BR TPACKET_V3 .
+.TP
+.BR PACKET_TIMESTAMP " (with " PACKET_RX_RING "; since Linux 2.6.36)"
+.\" commit 614f60fa9d73a9e8fdff3df83381907fea7c5649
+The packet receive ring always stores a timestamp in the metadata header.
+By default, this is a software generated timestamp generated when the
+packet is copied into the ring.
+This integer option selects the type of timestamp.
+Besides the default, it support the two hardware formats described in
+.IR Documentation/networking/timestamping.txt
+in the Linux kernel source tree.
+.TP
+.BR PACKET_TX_RING " (since Linux 2.6.31)"
+.\" commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1
+Create a memory-mapped ring buffer for packet transmission.
+This option is similar to
+.BR PACKET_RX_RING
+and takes the same arguments.
+The application writes packets into slots with
+.I tp_status
+equal to
+.BR TP_STATUS_AVAILABLE
+and schedules them for transmission by changing
+.I tp_status
+to
+.BR TP_STATUS_SEND_REQUEST .
+When packets are ready to be transmitted, the application calls
+.BR send (2)
+or a variant thereof.
+The
+.I buf
+and
+.I len
+fields of this call are ignored.
+If an address is passed using
+.BR sendto (2)
+or
+.BR sendmsg (2),
+then that overrides the socket default.
+On successful transmission, the socket resets
+.I tp_status
+to
+.BR TP_STATUS_AVAILABLE .
+It immediately aborts the transmission on error unless
+.BR PACKET_LOSS
+is set.
+.TP
+.BR PACKET_VERSION " (with " PACKET_RX_RING "; since Linux 2.6.27)"
+.\" commit bbd6ef87c544d88c30e4b762b1b61ef267a7d279
+By default,
+.BR PACKET_RX_RING
+creates a packet receive ring of variant
+.BR TPACKET_V1 .
+To create another variant, configure the desired variant by setting this
+integer option before creating the ring.
+.TP
+.BR PACKET_QDISC_BYPASS " (since Linux 3.14)"
+.\" commit d346a3fae3ff1d99f5d0c819bf86edf9094a26a1
+By default, packets sent through packet sockets pass through the kernel's
+qdisc (traffic control) layer, which is fine for the vast majority of use
+cases.
+For traffic generator appliances using packet sockets
+that intend to brute-force flood the network\(emfor example,
+to test devices under load in a similar
+fashion to pktgen\(emthis layer can be bypassed by setting
+this integer option to 1.
+A side effect is that packet buffering in the qdisc layer is avoided,
+which will lead to increased drops when network
+device transmit queues are busy;
+therefore, use at your own risk.
.SS Ioctls
.B SIOCGSTAMP
can be used to receive the timestamp of the last received packet.
Argument is a
-.I struct timeval.
+.I struct timeval
+variable.
.\" FIXME Document SIOCGSTAMPNS
-In addition all standard ioctls defined in
+In addition, all standard ioctls defined in
.BR netdevice (7)
and
.BR socket (7)
are valid on packet sockets.
-.SS Error Handling
+.SS Error handling
Packet sockets do no error handling other than errors occurred
while passing the packet to the device driver.
They don't have the concept of a pending error.
.B EPERM
User has insufficient privileges to carry out this operation.
-In addition other errors may be generated by the low-level driver.
+In addition, other errors may be generated by the low-level driver.
.SH VERSIONS
.B AF_PACKET
is a new feature in Linux 2.2.
.B AF_PACKET
via
.BR pcap (3);
-although this only covers a subset of the
+although this covers only a subset of the
.B AF_PACKET
features.
Incoming 802.3 packets are not multiplexed on the DSAP/SSAP protocol
fields; instead they are supplied to the user as protocol
.B ETH_P_802_2
-with the LLC header prepended.
+with the LLC header prefixed.
It is thus not possible to bind to
.BR ETH_P_802_3 ;
bind to
.\" This man page was written by Andi Kleen with help from Matthew Wilcox.
.\" AF_PACKET in Linux 2.2 was implemented
.\" by Alexey Kuznetsov, based on code by Alan Cox and others.
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR socket (2),
.BR pcap (3),
.BR capabilities (7),
.BR socket (7)
RFC\ 894 for the standard IP Ethernet encapsulation.
-
RFC\ 1700 for the IEEE 802.3 IP encapsulation.
The
.I <linux/if_ether.h>
include file for physical layer protocols.
+
+The Linux kernel source tree.
+.IR /Documentation/networking/filter.txt
+describes how to apply Berkeley Packet Filters to packet sockets.
+.IR /tools/testing/selftests/net/psock_tpacket.c
+contains example source code for all available versions of
+.BR PACKET_RX_RING
+and
+.BR PACKET_TX_RING .
+.SH COLOPHON
+This page is part of release 3.67 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.
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