sendmsg - Send a message from a socket using a message
structure
#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 );
Interfaces documented on this reference page conform to
industry standards as follows:
sendmsg(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the socket file descriptor. 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.
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. 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: Terminates
a record (if supported by the protocol).
Processes out-of-band data on sockets that support
out-of-band data. [Tru64 UNIX] Sends without
using routing tables. (Not recommended; for
debugging purposes only.)
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.
If the sending socket has no space to hold the message to
be transmitted, sendmsg() waits until space is available
unless the socket is in non-blocking I/O mode.
To broadcast on a socket, the application program must
first issue a setsockopt() function using the SO_BROADCAST
option to gain broadcast permissions.
Use the select() and poll() functions to determine when to
send more data.
[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.
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.
If the sendmsg() function fails, errno may be set to one
of the following values: Search permission is denied for a
component of the path prefix; or write access to the named
socket is denied. You cannot use addresses in the specified
address family with this socket. The socket parameter
is not valid. A peer forcibly closed a connection.
You did not specify a destination address for the connectionless
socket that also did not have its peer address
set. The message parameter; storage pointed to by the
msg_name, msg_control, or msg_iov fields of the message
parameter; or storage pointed to by the iovec structures
pointed to by the msg_iov field are not in a readable or
writable part of user address-space. The destination host
is unreachable. Possible reasons include the host is down
or the router has no route. A signal interrupted sendmsg
before any data was transmitted. The sum of the iov_len
values overflows an ssize_t. An I/O error occurred while
reading from or writing to the file system. The connection-oriented
socket for which a destination address was
specified is already connected. Too many symbolic links
were encountered in translating the pathname in the socket
address. The message is too large to be sent all at once,
as the socket requires.
The value of the msg_iovlen member of the msghdr
structure is less than or equal to zero (0) or is
greater than IOV_MAX. For AF_UNIX sockets, a component
of the pathname exceeded NAME_MAX characters,
or an entire pathname exceeded PATH_MAX characters.
The local network connection is not operational.
The destination network is unreachable.
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.
A component of the pathname does not name
an existing file or the pathname is an empty
string. The system did not have sufficient memory
to fulfill the request. The available STREAMS
resources were insufficient for the operation to
complete. A socket is connection-oriented but is
not connected. A component of the path prefix of
the pathname in address is not a directory. The
socket parameter refers to a file, not a socket.
The socket argument is associated with a socket
that does not support one or more of the values set
in flags. 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.
The socket is marked nonblocking, and no space is
available for the sendmsg() function.
Functions: recv(2), recvfrom(2), recvmsg(2), send(2),
sendto(2), shutdown(2), socket(2), select(2), getsockopt(2), setsockopt(2)
Standards: standards(5)
Network Programmer's Guide
sendmsg(2)
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