SENDMSG(3XNET)SENDMSG(3XNET)NAMEsendmsg - send a message on a socket using a message structure
SYNOPSIS
cc [ flag ... ] file ... -lxnet [ library ... ]
#include <sys/socket.h>
ssize_t sendmsg(int socket, const struct msghdr *message, int flags);
PARAMETERS
The function takes the following arguments:
socket
Specifies the socket file descriptor.
message
Points to a msghdr structure, containing both the destina‐
tion address and the buffers for the outgoing message. The
length and format of the address depend on the address fam‐
ily of the socket. The msg_flags member is ignored.
flags
Specifies the type of message transmission. The application
may specify 0 or the following flag:
MSG_EOR
Terminates a record (if supported by the proto‐
col)
MSG_OOB
Sends out-of-band data on sockets that support
out-of-bound data. The significance and semantics
of out-of-band data are protocol-specific.
DESCRIPTION
The sendmsg() function sends a message through a connection-mode or
connectionless-mode socket. If the socket is connectionless-mode, the
message will be sent to the address specified by msghdr. If the socket
is connection-mode, the destination address in msghdr is ignored.
The msg_iov and msg_iovlen fields of message specify zero or more
buffers containing the data to be sent. msg_iov points to an array of
iovec structures; msg_iovlen must be set to the dimension of this
array. In each iovec structure, the iov_base field specifies a stor‐
age area and the iov_len field gives its size in bytes. Some of these
sizes can be zero. The data from each storage area indicated by msg_iov
is sent in turn.
Successful completion of a call to sendmsg() does not guarantee deliv‐
ery of the message. A return value of −1 indicates only locally-
detected errors.
If space is not available at the sending socket to hold the message to
be transmitted and the socket file descriptor does not have O_NONBLOCK
set, sendmsg() function blocks until space is available. If space is
not available at the sending socket to hold the message to be transmit‐
ted and the socket file descriptor does have O_NONBLOCK set, sendmsg()
function will fail.
If the socket protocol supports broadcast and the specified address is
a broadcast address for the socket protocol, sendmsg() will fail if the
SO_BROADCAST option is not set for the socket.
The socket in use may require the process to have appropriate privi‐
leges to use the sendmsg() function.
USAGE
The select(3C) and poll(2) functions can be used to determine when it
is possible to send more data.
RETURN VALUES
Upon successful completion, sendmsg() function returns the number of
bytes sent. Otherwise, −1 is returned and errno is set to indicate the
error.
ERRORS
The sendmsg() function will fail if:
EAGAIN
EWOULDBLOCK
The socket's file descriptor is marked O_NONBLOCK and
the requested operation would block.
EAFNOSUPPORT
Addresses in the specified address family cannot be
used with this socket.
EBADF
The socket argument is not a valid file descriptor.
ECONNRESET
A connection was forcibly closed by a peer.
EFAULT
The message parameter, or storage pointed to by the
msg_name, msg_control or msg_iov fields of the mes‐
sage parameter, or storage pointed to by the iovec
structures pointed to by the msg_iov field can not be
accessed.
EINTR
A signal interrupted sendmsg() before any data was
transmitted.
EINVAL
The sum of the iov_len values overflows an ssize_t.
EMSGSIZE
The message is to large to be sent all at once (as the
socket requires), or the msg_iovlen member of the
msghdr structure pointed to by message is less than or
equal to 0 or is greater than IOV_MAX.
ENOTCONN
The socket is connection-mode but is not connected.
ENOTSOCK
The socket argument does not refer a socket.
EOPNOTSUPP
The socket argument is associated with a socket that
does not support one or more of the values set in
flags.
EPIPE
The socket is shut down for writing, or the socket is
connection-mode and is no longer connected. In the lat‐
ter case, and if the socket is of type SOCK_STREAM, the
SIGPIPE signal is generated to the calling thread.
If the address family of the socket is AF_UNIX, then sendmsg() will
fail if:
EIO
An I/O error occurred while reading from or writing to
the file system.
ELOOP
Too many symbolic links were encountered in translating
the pathname in the socket address.
ENAMETOOLONG
A component of a pathname exceeded NAME_MAX characters,
or an entire pathname exceeded PATH_MAX characters.
ENOENT
A component of the pathname does not name an existing
file or the pathname is an empty string.
ENOTDIR
A component of the path prefix of the pathname in the
socket address is not a directory.
The sendmsg() function may fail if:
EACCES
Search permission is denied for a component of the path
prefix; or write access to the named socket is denied.
EDESTADDRREQ
The socket is not connection-mode and does not have its
peer address set, and no destination address was speci‐
fied.
EHOSTUNREACH
The destination host cannot be reached (probably
because the host is down or a remote router cannot
reach it).
EIO
An I/O error occurred while reading from or writing to
the file system.
EISCONN
A destination address was specified and the socket is
already connected.
ENETDOWN
The local interface used to reach the destination is
down.
ENETUNREACH
No route to the network is present.
ENOBUFS
Insufficient resources were available in the system to
perform the operation.
ENOMEM
Insufficient memory was available to fulfill the
request.
ENOSR
There were insufficient STREAMS resources available for
the operation to complete.
If the address family of the socket is AF_UNIX, then sendmsg() may fail
if:
ENAMETOOLONG
Pathname resolution of a symbolic link produced an
intermediate result whose length exceeds PATH_MAX.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
├────────────────────┼─────────────────┤
│MT-Level │ MT-Safe │
└────────────────────┴─────────────────┘
SEE ALSOpoll(2)getsockopt(3XNET), recv(3XNET), recvfrom(3XNET),
recvmsg(3XNET), select(3C), send(3XNET), sendto(3XNET), setsock‐
opt(3XNET), shutdown(3XNET), socket(3XNET), attributes(5), standards(5)
Nov 1, 2003 SENDMSG(3XNET)
