sendmmsg Subroutine

Purpose

Sends multiple messages from a socket by using a message structure.

Syntax

       #include  <sys/types.h>
       #include  <sys/socketvar.h>
       #include  <sys/socket.h>

       int sendmmsg (Socket, Messages, Flags)

       int Socket;

       struct mmsghdr Message [];

       int Flags;

Description

The sendmmsg subroutine sends messages through the connected or unconnected sockets by using the mmsghdr message structure. The /usr/include/sys/socket.h file contains the mmsghdr message structure and defines the structure members. This subroutine is an extension to the sendmsg subroutine.

Parameters

Socket: Specifies the socket descriptor.
Messages: Points to an array of mmsghdr message structures that contain the messages to be sent.
Flags: Allows the sender to control the message transmission. The Flags parameter that is used to send a call is formed by logically ORing the flag values. The sendmmsg subroutine accepts the same flag values as the sendmsg subroutine. The sys/socket.h file contains the Flags parameter.

Return values

Upon successful completion, the sendmmsg subroutine returns the number of sent messages.

The sendmmsg subroutine updates the msg_len attribute of each mmsghdr structure to indicate the number of bytes that are sent from the corresponding message.

If the sendmmsg subroutine is unsuccessful, the system handler performs the following functions:

Returns a value of -1 to the calling program.
Moves an error code, which indicates the specific error, into the errno global variable.

Error codes

The sendmmsg subroutine is unsuccessful if any of the following errors occur:

Error	Description
EACCES	Write access to the named socket is denied, or the socket that is trying to send a broadcast packet does not have the broadcast capability.
EADDRNOTAVAIL	The specified address is not a valid address.
EAFNOSUPPORT	The specified address is not a valid address for the address family of the socket.
EBADF	The Socket parameter is not valid.
ECONNRESET	A connection was forcibly closed by a peer.
EDESTADDRREQ	The socket is not in connection-mode and does not have its peer address set.
EFAULT	The Address parameter is not in a writable part of the user address space.
EHOSTUNREACH	The destination host cannot be reached.
EINTR	A signal interrupted the sendmmsg subroutine before any data was transmitted.
EINVAL	The length of the `msghdr` structure is invalid.
EISCONN	The `SOCK_DGRAM` socket is already connected.
EMSGSIZE	The message is too large to be sent together (as per the socket requirement), or the `msg_iovlen` member of the `msghdr` structure pointed to by the Messages parameter is less than or equal to 0 or is greater than the `IOV_MAX` value.
ENOENT	The path name does not point an existing file, or the path name is an empty string.
ENETUNREACH	The destination network is not reachable.
ENOBUFS	The system ran out of memory for an internal data structure.
ENOMEM	The available data space in memory is not large enough to hold group information or access control list (ACL) information.
ENOPROTOOPT	The protocol does not support 64 bits.
ENOTCONN	The socket is in connection-mode but is not connected.
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 that are set in the Flags parameter.
EPIPE	An attempt was made to send on a socket that was connected, but the connection is shut down either by the remote peer or by the socket side of the connection. If the socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the calling process.
EWOULDBLOCK	The socket is marked as `nonblocking`, and no connections are present to be accepted.