trusty (3) sendmsg.3posix.gz

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NAME
       sendmsg - send a message on a socket using a message structure


SYNOPSIS
       #include <sys/socket.h>

       ssize_t sendmsg(int socket, const struct msghdr *message, int flags);


DESCRIPTION
       The  sendmsg()  function shall send a message through a connection-mode or connectionless-mode socket. If
       the socket is connectionless-mode, the message shall be sent to the address specified by msghdr.  If  the
       socket is connection-mode, the destination address in msghdr shall be ignored.

       The sendmsg() function takes the following arguments:

       socket Specifies the socket file descriptor.

       message
              Points  to  a  msghdr  structure,  containing both the destination address and the buffers for the
              outgoing message. The length and format of the address depend on the address family 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 protocol).

       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.

       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 shall be set to the dimension of this array.
       In each iovec structure, the iov_base field specifies a storage 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 delivery 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, the sendmsg() function shall block until space is available.  If
       space  is  not  available at the sending socket to hold the message to be transmitted and the socket file
       descriptor does have O_NONBLOCK set, the sendmsg() function shall fail.

       If the socket protocol supports broadcast and the specified address is a broadcast address for the socket
       protocol, sendmsg() shall fail if the SO_BROADCAST option is not set for the socket.

       The socket in use may require the process to have appropriate privileges to use the sendmsg() function.


RETURN VALUE
       Upon  successful  completion,  sendmsg()  shall  return  the number of bytes sent. Otherwise, -1 shall be
       returned and errno set to indicate the error.


ERRORS
       The sendmsg() function shall fail if:

       EAGAIN or 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.

       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 too 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 to 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 latter 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() shall fail if:

       EIO    An I/O error occurred while reading from or writing to the file system.

       ELOOP  A  loop  exists  in  symbolic  links  encountered  during resolution of 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 path name 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 specified.

       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 network 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.

       If the address family of the socket is AF_UNIX, then sendmsg() may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the pathname  in  the
              socket address.

       ENAMETOOLONG
              Pathname  resolution  of  a  symbolic  link  produced  an intermediate result whose length exceeds
              {PATH_MAX}.

       The following sections are informative.


EXAMPLES
       Done.


APPLICATION USAGE
       The select() and poll() functions can be used to determine when it is possible to send more data.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       getsockopt() , poll() , recv() , recvfrom() , recvmsg() , select() , send() , sendto() ,  setsockopt()  ,
       shutdown() , socket() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .