+ qemu-discuss@nongnu.org back.
On 9/10/24 1:15 PM, DUO Labs wrote:
> Should the fd be sent through SCM_RIGHTS just before the getfd command, or can
> you somehow combine the two messages into one?
It is one simple cmsghdr message, with both the getfd qmp message, and also the
fd/SCM_RIGHTS.
I suggest read the libvirt code.
465 /**
466 * virSocketSendMsgWithFDs:
467 * @sock: socket to send payload and fds to
468 * @payload: payload to send
469 * @payload_len: length of @payload
470 * @fds: array of fds to send
471 * @fds_len: len of fds array
472
473 * Send @fds along with @payload to @sock using SCM_RIGHTS.
474 * Return number of bytes sent on success.
475 * On error, set errno and return -1.
476 */
477 int
478 virSocketSendMsgWithFDs(int sock,
479 const char *payload,
480 size_t payload_len,
481 int *fds,
482 size_t fds_len)
483 {
484 g_autofree char *control = NULL;
485 const size_t control_size = CMSG_SPACE(sizeof(int) * fds_len);
486 struct cmsghdr *cmsg;
487 struct msghdr msg = { 0 };
488 struct iovec iov[1]; /* Send a single payload, so set vector len to 1 */
489 int ret;
490
491 control = g_new0(char, control_size);
492
493 iov[0].iov_base = (void *) payload;
494 iov[0].iov_len = payload_len;
495
496 msg.msg_iov = iov;
497 msg.msg_iovlen = 1;
498
499 msg.msg_control = control;
500 msg.msg_controllen = control_size;
501
502 cmsg = CMSG_FIRSTHDR(&msg);
503 /* check to eliminate "potential null pointer dereference" errors during
build */
504 if (!cmsg) {
505 errno = ENOSPC;
506 return -1;
507 }
508
509 cmsg->cmsg_len = CMSG_LEN(sizeof(int) * fds_len);
510 cmsg->cmsg_level = SOL_SOCKET;
511 cmsg->cmsg_type = SCM_RIGHTS;
512 memcpy(CMSG_DATA(cmsg), fds, sizeof(int) * fds_len);
513
514 do {
515 ret = sendmsg(sock, &msg, 0);
516 } while (ret < 0 && errno == EINTR);
517
518 return ret;
519 }
Dongli Zhang
