Merging upstream version 6.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 0 insertions, 312 deletions

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-.\" SPDX-License-Identifier: Linux-man-pages-1-para
-.\"
-.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
-.\"
-.\" $Id: udp.7,v 1.7 2000/01/22 01:55:05 freitag Exp $
-.\"
-.TH udp 7 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-udp \- User Datagram Protocol for IPv4
-.SH SYNOPSIS
-.nf
-.B #include <sys/socket.h>
-.B #include <netinet/in.h>
-.B #include <netinet/udp.h>
-.P
-.IB udp_socket " = socket(AF_INET, SOCK_DGRAM, 0);"
-.fi
-.SH DESCRIPTION
-This is an implementation of the User Datagram Protocol
-described in RFC\ 768.
-It implements a connectionless, unreliable datagram packet service.
-Packets may be reordered or duplicated before they arrive.
-UDP generates and checks checksums to catch transmission errors.
-.P
-When a UDP socket is created,
-its local and remote addresses are unspecified.
-Datagrams can be sent immediately using
-.BR sendto (2)
-or
-.BR sendmsg (2)
-with a valid destination address as an argument.
-When
-.BR connect (2)
-is called on the socket, the default destination address is set and
-datagrams can now be sent using
-.BR send (2)
-or
-.BR write (2)
-without specifying a destination address.
-It is still possible to send to other destinations by passing an
-address to
-.BR sendto (2)
-or
-.BR sendmsg (2).
-In order to receive packets, the socket can be bound to a local
-address first by using
-.BR bind (2).
-Otherwise, the socket layer will automatically assign
-a free local port out of the range defined by
-.I /proc/sys/net/ipv4/ip_local_port_range
-and bind the socket to
-.BR INADDR_ANY .
-.P
-All receive operations return only one packet.
-When the packet is smaller than the passed buffer, only that much
-data is returned; when it is bigger, the packet is truncated and the
-.B MSG_TRUNC
-flag is set.
-.B MSG_WAITALL
-is not supported.
-.P
-IP options may be sent or received using the socket options described in
-.BR ip (7).
-They are processed by the kernel only when the appropriate
-.I /proc
-parameter
-is enabled (but still passed to the user even when it is turned off).
-See
-.BR ip (7).
-.P
-When the
-.B MSG_DONTROUTE
-flag is set on sending, the destination address must refer to a local
-interface address and the packet is sent only to that interface.
-.P
-By default, Linux UDP does path MTU (Maximum Transmission Unit) discovery.
-This means the kernel
-will keep track of the MTU to a specific target IP address and return
-.B EMSGSIZE
-when a UDP packet write exceeds it.
-When this happens, the application should decrease the packet size.
-Path MTU discovery can be also turned off using the
-.B IP_MTU_DISCOVER
-socket option or the
-.I /proc/sys/net/ipv4/ip_no_pmtu_disc
-file; see
-.BR ip (7)
-for details.
-When turned off, UDP will fragment outgoing UDP packets
-that exceed the interface MTU.
-However, disabling it is not recommended
-for performance and reliability reasons.
-.SS Address format
-UDP uses the IPv4
-.I sockaddr_in
-address format described in
-.BR ip (7).
-.SS Error handling
-All fatal errors will be passed to the user as an error return even
-when the socket is not connected.
-This includes asynchronous errors
-received from the network.
-You may get an error for an earlier packet
-that was sent on the same socket.
-This behavior differs from many other BSD socket implementations
-which don't pass any errors unless the socket is connected.
-Linux's behavior is mandated by
-.BR RFC\ 1122 .
-.P
-For compatibility with legacy code, in Linux 2.0 and 2.2
-it was possible to set the
-.B SO_BSDCOMPAT
-.B SOL_SOCKET
-option to receive remote errors only when the socket has been
-connected (except for
-.B EPROTO
-and
-.BR EMSGSIZE ).
-Locally generated errors are always passed.
-Support for this socket option was removed in later kernels; see
-.BR socket (7)
-for further information.
-.P
-When the
-.B IP_RECVERR
-option is enabled, all errors are stored in the socket error queue,
-and can be received by
-.BR recvmsg (2)
-with the
-.B MSG_ERRQUEUE
-flag set.
-.SS /proc interfaces
-System-wide UDP parameter settings can be accessed by files in the directory
-.IR /proc/sys/net/ipv4/ .
-.TP
-.IR udp_mem " (since Linux 2.6.25)"
-This is a vector of three integers governing the number
-of pages allowed for queueing by all UDP sockets.
-.RS
-.TP
-.I min
-Below this number of pages, UDP is not bothered about its
-memory appetite.
-When the amount of memory allocated by UDP exceeds
-this number, UDP starts to moderate memory usage.
-.TP
-.I pressure
-This value was introduced to follow the format of
-.I tcp_mem
-(see
-.BR tcp (7)).
-.TP
-.I max
-Number of pages allowed for queueing by all UDP sockets.
-.RE
-.IP
-Defaults values for these three items are
-calculated at boot time from the amount of available memory.
-.TP
-.IR udp_rmem_min " (integer; default value: PAGE_SIZE; since Linux 2.6.25)"
-Minimal size, in bytes, of receive buffers used by UDP sockets in moderation.
-Each UDP socket is able to use the size for receiving data,
-even if total pages of UDP sockets exceed
-.I udp_mem
-pressure.
-.TP
-.IR udp_wmem_min " (integer; default value: PAGE_SIZE; since Linux 2.6.25)"
-Minimal size, in bytes, of send buffer used by UDP sockets in moderation.
-Each UDP socket is able to use the size for sending data,
-even if total pages of UDP sockets exceed
-.I udp_mem
-pressure.
-.SS Socket options
-To set or get a UDP socket option, call
-.BR getsockopt (2)
-to read or
-.BR setsockopt (2)
-to write the option with the option level argument set to
-.BR IPPROTO_UDP .
-Unless otherwise noted,
-.I optval
-is a pointer to an
-.IR int .
-.P
-Following is a list of UDP-specific socket options.
-For details of some other socket options that are also applicable
-for UDP sockets, see
-.BR socket (7).
-.TP
-.BR UDP_CORK " (since Linux 2.5.44)"
-If this option is enabled, then all data output on this socket
-is accumulated into a single datagram that is transmitted when
-the option is disabled.
-This option should not be used in code intended to be
-portable.
-.\" FIXME document UDP_ENCAP (new in Linux 2.5.67)
-.\" From include/linux/udp.h:
-.\"     UDP_ENCAP_ESPINUDP_NON_IKE draft-ietf-ipsec-nat-t-ike-00/01
-.\"     UDP_ENCAP_ESPINUDP draft-ietf-ipsec-udp-encaps-06
-.\"     UDP_ENCAP_L2TPINUDP rfc2661
-.\" FIXME Document UDP_NO_CHECK6_TX and UDP_NO_CHECK6_RX, added in Linux 3.16
-.TP
-.BR UDP_SEGMENT " (since Linux 4.18)"
-Enables UDP segmentation offload.
-Segmentation offload reduces
-.BR send (2)
-cost by transferring multiple datagrams worth of data
-as a single large packet through the kernel transmit path,
-even when that exceeds MTU.
-As late as possible,
-the large packet is split by segment size into a series of datagrams.
-This segmentation offload step is deferred to hardware if supported,
-else performed in software.
-This option takes a value in the range
-.RB [ 0 ,\~ USHRT_MAX ]
-that sets the segment size:
-the size of datagram payload,
-excluding the UDP header.
-The segment size must be chosen such that
-at most 64 datagrams are sent in a single call
-and that the datagrams after segmentation meet
-the same MTU rules that apply to datagrams sent without this option.
-Segmentation offload depends on checksum offload,
-as datagram checksums are computed after segmentation.
-The option may also be set for individual
-.BR sendmsg (2)
-calls by passing it as a
-.BR cmsg (3).
-A value of zero disables the feature.
-This option should not be used in code intended to be portable.
-.TP
-.BR UDP_GRO " (since Linux 5.0)"
-Enables UDP receive offload.
-If enabled,
-the socket may receive multiple datagrams worth of data
-as a single large buffer,
-together with a
-.BR cmsg (3)
-that holds the segment size.
-This option is the inverse of segmentation offload.
-It reduces receive cost by handling multiple datagrams worth of data
-as a single large packet in the kernel receive path,
-even when that exceeds MTU.
-This option should not be used in code intended to be portable.
-.SS Ioctls
-These ioctls can be accessed using
-.BR ioctl (2).
-The correct syntax is:
-.P
-.RS
-.nf
-.BI int " value";
-.IB error " = ioctl(" udp_socket ", " ioctl_type ", &" value ");"
-.fi
-.RE
-.TP
-.BR FIONREAD " (" SIOCINQ )
-Gets a pointer to an integer as argument.
-Returns the size of the next pending datagram in the integer in bytes,
-or 0 when no datagram is pending.
-.B Warning:
-Using
-.BR FIONREAD ,
-it is impossible to distinguish the case where no datagram is pending
-from the case where the next pending datagram contains zero bytes of data.
-It is safer to use
-.BR select (2),
-.BR poll (2),
-or
-.BR epoll (7)
-to distinguish these cases.
-.\" See http://www.securiteam.com/unixfocus/5KP0I15IKO.html
-.\" "GNUnet DoS (UDP Socket Unreachable)", 14 May 2006
-.TP
-.BR TIOCOUTQ " (" SIOCOUTQ )
-Returns the number of data bytes in the local send queue.
-Supported only with Linux 2.4 and above.
-.P
-In addition, all ioctls documented in
-.BR ip (7)
-and
-.BR socket (7)
-are supported.
-.SH ERRORS
-All errors documented for
-.BR socket (7)
-or
-.BR ip (7)
-may be returned by a send or receive on a UDP socket.
-.TP
-.B ECONNREFUSED
-No receiver was associated with the destination address.
-This might be caused by a previous packet sent over the socket.
-.SH VERSIONS
-.B IP_RECVERR
-is a new feature in Linux 2.2.
-.\" .SH CREDITS
-.\" This man page was written by Andi Kleen.
-.SH SEE ALSO
-.BR ip (7),
-.BR raw (7),
-.BR socket (7),
-.BR udplite (7)
-.P
-The kernel source file
-.IR Documentation/networking/ip\-sysctl.txt .
-.P
-RFC\ 768 for the User Datagram Protocol.
-.br
-RFC\ 1122 for the host requirements.
-.br
-RFC\ 1191 for a description of path MTU discovery.