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#define _GNU_SOURCE #include <sys/socket.h> int recvmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen,
unsigned int flags, struct timespec *timeout);
The sockfd argument is the file descriptor of the socket to receive data from.
The msgvec argument is a pointer to an array of mmsghdr structures. The size of this array is specified in vlen.
The mmsghdr structure is defined in <sys/socket.h> as:
struct mmsghdr { struct msghdr msg_hdr; /* Message header */ unsigned int msg_len; /* Number of received bytes for header */ };
The msg_hdr field is a msghdr structure, as described in recvmsg(2). The msg_len field is the number of bytes returned for the message in the entry. This field has the same value as the return value of a single recvmsg(2) on the header.
The flags argument contains flags ORed together. The flags are the same as documented for recvmsg(2), with the following addition:
The timeout argument points to a struct timespec (see clock_gettime(2)) defining a timeout (seconds plus nanoseconds) for the receive operation. If timeout is NULL then the operation blocks indefinitely.
A blocking recvmmsg() call blocks until vlen messages have been received or until the timeout expires. A nonblocking call reads as many messages as are available (up to the limit specified by vlen) and returns immediately.
On return from recvmmsg(), successive elements of msgvec are updated to contain information about each received message: msg_len contains the size of the received message; the subfields of msg_hdr are updated as described in recvmsg(2). The return value of the call indicates the number of elements of msgvec that have been updated.