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sendmsg(2)
NAME
sendmsg - Sends a message from a socket using a message structure
SYNOPSIS
#include <sys/socket.h>
ssize_t sendmsg (
int socket,
const struct msghdr *message,
int flags);
[Tru64 UNIX] The following definition of the sendmsg() function does not
conform to current standards and is supported only for backward
compatibility (see standards(5)):
int sendmsg (
int socket,
struct msghdr *message,
int flags);
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
sendmsg(): XNS4.0
The sendmsg function also supports POSIX.1g Draft 6.6.
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
socket Specifies the socket file descriptor.
message Points to a msghdr structure, containing pointers to both the
destination address for the outgoing message and to buffers
containing ancillary data. The format of the address is
determined by the behavior requested for the socket.
[POSIX] In POSIX.1g Draft 6.6 the msghdr structure uses a
socklen_t data type for the msg_iovlen field instead of a size_t
data type as specified in XNS4.0.
[Tru64 UNIX] If the compile-time option _SOCKADDR_LEN is
defined before the <sys/socket.h> header file is included, the
msghdr structure takes 4.4BSD behavior. Otherwise, the default
4.3BSD msghdr structure is used.
In 4.4BSD, the msghdr structure has a separate msg_flags field
for holding flags from the received message. In addition, the
msg_accrights field is generalized into a msg_control field. See
the recvmsg() function for more information.
If _SOCKADDR_LEN is defined, the 4.3BSD msghdr structure is
defined with the name omsghdr.
flags Allows the sender to control the message transmission. The
<sys/socket.h> file contains the flags values. The flags value
to send a call is formed by a logical OR of one or both of the
following values:
MSG_OOB Processes out-of-band data on sockets that support
out-of-band data.
MSG_DONTROUTE Sends without using routing tables. (Not
recommended, for debugging purposes only.)
DESCRIPTION
The sendmsg() function sends messages through connected or unconnected
sockets using the msghdr message structure. This minimizes the number of
directly supplied parameters to the function call. The <sys/socket.h> file
contains the msghdr structure and defines the structure members.
To broadcast on a socket, the application program must first issue a
setsockopt() function using the SO_BROADCAST option to gain broadcast
permissions.
NOTES
[Tru64 UNIX] When compiled in the X/Open UNIX environment, calls to the
sendmsg() function are internally renamed by prepending _E to the function
name. When you are debugging a module that includes the sendmsg() function
and for which _XOPEN_SOURCE_EXTENDED has been defined, use _Esendmsg to
refer to the sendmsg() call. See standards(5) for further information.
[Tru64 UNIX] When compiled in the POSIX.1g socket environment, calls to
the sendmsg() function are internally renamed by prepending _P to the
function name. When you are debugging a module that includes the sendmsg()
function and for which _POSIX_PII_SOCKET has been defined, use _Psendmsg to
refer to the sendmsg() call. See standards(5) for further information.
RETURN VALUES
Upon successful completion, the sendmsg() function returns the number of
characters sent. Otherwise, a value of -1 is returned and errno is set to
indicate the error.
ERRORS
If the sendmsg() function fails, errno may be set to one of the following
values:
[EACCESS] For an AF_UNIX socket, search permission is denied for a
component of the path prefix; or write access to the named
socket is denied.
[EAFNOSUPPORT] Addresses in the specified address family cannot be used
with this socket.
[EBADF] The socket parameter is not valid.
[ECONNRESET] A connection was forcibly closed by a peer.
[EDESTADDRREQ] You did not specify a destination address for the
connectionless socket that also did not have its peer
address set.
[EHOSTUNREACH] The destination host is unreachable. Possible reasons
include the host is down or the router has no route.
[EINTR] A signal interrupted sendmsg before any data was
transmitted.
[EINVAL] The sum of the iov_len values overflows an ssize_t.
[EIO] For an AF_UNIX socket, an I/O error occurred while reading
from or writing to the file system.
[EISCONN] The connection-oriented socket for which a destination
address was specified is already connected.
[ELOOP] For an AF_UNIX socket, too many symbolic links were
encountered in translating the pathname in the socket
address.
[EMSGSIZE] The message is too large to be sent all at once, as the
socket requires.
[ENAMETOOLONG] For an AF_UNIX socket, a component of the pathname exceeded
NAME_MAX characters, or an entire pathname exceeded PATH_MAX
characters.
[ENETDOWN] The local network connection is not operational.
[ENETUNREACH] The destination network is unreachable.
[ENOBUFS] Insufficient resources were available in the system to
complete the call.
[Tru64 UNIX] The interface driver's send queue is full. If
the problem persists, you might increase the value for the
ifqmaxlen system attribute in the net subsystem. See
sys_attrs_net(5) for more information.
[ENOENT] For an AF_UNIX socket, a component of the pathname does not
name an existing file or the pathname is an empty string.
[ENOMEM] The system did not have sufficient memory to fulfill the
request.
[ENOSR] The available STREAMS resources were insufficient for the
operation to complete.
[ENOTCONN] A socket is connection-oriented but is not connected.
[ENOTDIR] For an AF_UNIX socket, a component of the path prefix of the
pathname in address is not a directory.
[ENOTSOCK] The socket parameter refers to a file, not 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-oriented and the peer is closed or shut down for
reading. In the latter case, and if the socket is of type
SOCK_STREAM, the SIGPIPE signal is generated to the calling
process.
[EWOULDBLOCK] The socket is marked nonblocking, and no space is available
for the sendmsg() function.
RELATED INFORMATION
Functions: recv(2), recvfrom(2), recvmsg(2), send(2), sendto(2),
shutdown(2), socket(2), select(2), getsockopt(2), setsockopt(2)
Standards: standards(5)
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