sendfd.c

unix环境高级编程的源代码

#include    <sys/types.h>
#include    <sys/socket.h>        /* struct msghdr */
#include    <sys/uio.h>            /* struct iovec */
#include    <errno.h>
#include    <stddef.h>
#include    "ourhdr.h"

static struct cmsghdr    *cmptr = NULL;    /* buffer is malloc'ed first time */
#define    CONTROLLEN    (sizeof(struct cmsghdr) + sizeof(int))
        /* size of control buffer to send/recv one file descriptor */

/* Pass a file descriptor to another process.
 * If fd<0, then -fd is sent back instead as the error status. */

int
send_fd(int clifd, int fd)
{
    struct iovec    iov[1];
    struct msghdr    msg;
    char            buf[2];    /* send_fd()/recv_fd() 2-byte protocol */

    iov[0].iov_base = buf;
    iov[0].iov_len  = 2;
    msg.msg_iov     = iov;
    msg.msg_iovlen  = 1;
    msg.msg_name    = NULL;
    msg.msg_namelen = 0;
    if (fd < 0) {
        msg.msg_control    = NULL;
        msg.msg_controllen = 0;
        buf[1] = -fd;    /* nonzero status means error */
        if (buf[1] == 0)
            buf[1] = 1;    /* -256, etc. would screw up protocol */
    } else {
        if (cmptr == NULL && (cmptr = malloc(CONTROLLEN)) == NULL)
            return(-1);
        cmptr->cmsg_level  = SOL_SOCKET;
        cmptr->cmsg_type   = SCM_RIGHTS;
        cmptr->cmsg_len    = CONTROLLEN;
        msg.msg_control    = (caddr_t) cmptr;
        msg.msg_controllen = CONTROLLEN;
        *(int *)CMSG_DATA(cmptr) = fd;        /* the fd to pass */
        buf[1] = 0;        /* zero status means OK */
    }
    buf[0] = 0;            /* null byte flag to recv_fd() */

    if (sendmsg(clifd, &msg, 0) != 2)
        return(-1);
    return(0);
}