passfd: Fix compilation error on IRIX

[Bruno Haible]

On IRIX 6.5, the passfd module does not compile any more, since the
headers now define CMSG_FIRSTHDR.

passfd.c: In function `sendfd':
passfd.c:57: warning: implicit declaration of function `CMSG_SPACE'
passfd.c:74: error: `SCM_RIGHTS' undeclared (first use in this function)
passfd.c:74: error: (Each undeclared identifier is reported only once
passfd.c:74: error: for each function it appears in.)
passfd.c:75: warning: implicit declaration of function `CMSG_LEN'
passfd.c: In function `recvfd':
passfd.c:141: error: `SCM_RIGHTS' undeclared (first use in this function)

But this implementation of passfd, even with fallback definitions of
CMSG_SPACE, CMSG_LEN, SCM_RIGHTS would not work. Therefore this patch.


2021-12-24  Bruno Haible  <br...@clisp.org>

        passfd: Fix compilation error on IRIX.
        * lib/passfd.c (sendfd): On IRIX, ignore CMSG_FIRSTHDR.
        (recvfd): Likewise. Produce a fake error ENOTCONN.

diff --git a/lib/passfd.c b/lib/passfd.c
index 8a3b7bd10..e22419a3c 100644
--- a/lib/passfd.c
+++ b/lib/passfd.c
@@ -52,7 +52,7 @@ sendfd (int sock, int fd)
   char byte = 0;
   struct iovec iov;
   struct msghdr msg;
-# ifdef CMSG_FIRSTHDR
+# if defined CMSG_FIRSTHDR && !defined __sgi
   struct cmsghdr *cmsg;
   char buf[CMSG_SPACE (sizeof fd)];
 # endif
@@ -66,7 +66,7 @@ sendfd (int sock, int fd)
   msg.msg_name = NULL;
   msg.msg_namelen = 0;
 
-# ifdef CMSG_FIRSTHDR
+# if defined CMSG_FIRSTHDR && !defined __sgi
   msg.msg_control = buf;
   msg.msg_controllen = sizeof buf;
   cmsg = CMSG_FIRSTHDR (&msg);
@@ -112,7 +112,7 @@ recvfd (int sock, int flags)
   struct msghdr msg;
   int fd = -1;
   ssize_t len;
-# ifdef CMSG_FIRSTHDR
+# if defined CMSG_FIRSTHDR && !defined __sgi
   struct cmsghdr *cmsg;
   char buf[CMSG_SPACE (sizeof fd)];
   int flags_recvmsg = flags & O_CLOEXEC ? MSG_CMSG_CLOEXEC : 0;
@@ -133,7 +133,7 @@ recvfd (int sock, int flags)
   msg.msg_name = NULL;
   msg.msg_namelen = 0;
 
-# ifdef CMSG_FIRSTHDR
+# if defined CMSG_FIRSTHDR && !defined __sgi
   msg.msg_control = buf;
   msg.msg_controllen = sizeof buf;
   cmsg = CMSG_FIRSTHDR (&msg);
@@ -193,6 +193,9 @@ recvfd (int sock, int flags)
           return -1;
         }
     }
+
+  if (fd < 0 && errno == 0)
+    errno = ENOTCONN;
 # else
   errno = ENOSYS;
 # endif