From 7530e8cdd506ecec1f4ad3bbd55f94de5a6d63ac Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Mon, 26 Oct 2020 14:21:53 +0000
Subject:  Separate and expose ancil_recv_fd/ancil_send_fd

 The goal is to make late channel creation easy, as opposed to
textclient which always creates a new channel at start time.

 This commit also moves posixishard.h inclusions as late as possible.
---
 src/libunixonacid/ancil_send_fd.c | 45 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 src/libunixonacid/ancil_send_fd.c

(limited to 'src/libunixonacid/ancil_send_fd.c')

diff --git a/src/libunixonacid/ancil_send_fd.c b/src/libunixonacid/ancil_send_fd.c
new file mode 100644
index 0000000..98366c7
--- /dev/null
+++ b/src/libunixonacid/ancil_send_fd.c
@@ -0,0 +1,45 @@
+/* ISC license. */
+
+#include <skalibs/nonposix.h>
+
+#include <errno.h>
+#include <string.h>
+#include <sys/uio.h>
+#include <sys/socket.h>
+
+#include <skalibs/djbunix.h>
+#include <skalibs/ancil.h>
+#include <skalibs/posixishard.h>
+
+union aligner_u
+{
+  struct cmsghdr cmsghdr ;
+  int i ;
+} ;
+
+int ancil_send_fd (int sock, int fd, char ch)
+{
+  ssize_t r ;
+  struct iovec v = { .iov_base = &ch, .iov_len = 1 } ;
+  union aligner_u ancilbuf[1 + (CMSG_SPACE(sizeof(int)) - 1) / sizeof(union aligner_u)] ;
+  struct msghdr hdr =
+  {
+    .msg_name = 0,
+    .msg_namelen = 0,
+    .msg_iov = &v,
+    .msg_iovlen = 1,
+    .msg_control = ancilbuf,
+    .msg_controllen = CMSG_SPACE(sizeof(int))
+  } ;
+  struct cmsghdr *c = CMSG_FIRSTHDR(&hdr) ;
+  memset(hdr.msg_control, 0, hdr.msg_controllen) ;
+  c->cmsg_level = SOL_SOCKET ;
+  c->cmsg_type = SCM_RIGHTS ;
+  c->cmsg_len = CMSG_LEN(sizeof(int)) ;
+  *(int *)CMSG_DATA(c) = fd ;
+  do r = sendmsg(sock, &hdr, MSG_NOSIGNAL) ;
+  while (r < 0 && errno == EINTR) ;
+  if (r <= 0) return 0 ;
+  fd_close(fd) ;
+  return 1 ;
+}
-- 
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