sendmsg

Prototype

int sendmsg(int s, caddr_t msg, int flags);

Returns: int

Arguments

Version history

Examples

char buf[CMSG_SPACE(sizeof(int))] = {0};
struct iovec iov = { .iov_base = "x", .iov_len = 1 };
struct msghdr msg = { .msg_iov = &iov, .msg_iovlen = 1,
                      .msg_control = buf, .msg_controllen = sizeof(buf) };
struct cmsghdr *c = CMSG_FIRSTHDR(&msg);
c->cmsg_level = SOL_SOCKET; c->cmsg_type = SCM_RIGHTS;
c->cmsg_len = CMSG_LEN(sizeof(int));
*(int *)CMSG_DATA(c) = fd_to_pass;
sendmsg(sock, &msg, 0);

Notes

Mirror of recvmsg on the send side. It is the only entry point that can attach SCM_RIGHTS (file-descriptor passing) on AF_UNIX, set IP_PKTINFO source addresses, or carry NECP_CLIENT_PARAMETER cmsgs that bind a UDP packet to a specific Network.framework path. msghdr.msg_flags is ignored on input; only the iov, cmsg, and destination matter.

Detection

ES has no sendmsg event. NEFilterDataProvider sees payload bytes; descriptor passing via SCM_RIGHTS can be inferred by comparing PROC_PIDFDSOCKETINFO snapshots across peers.

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