So the non-portable MSG_DONTWAIT may alleviate the problem... might

as well use it on architectures that support it.

4 files changed, 32 insertions, 15 deletions

diff --git a/configure b/configure
index ba4439a..389b31b 100755
--- a/configure
+++ b/configure
@@ -442,7 +442,8 @@ EOF
   choose cl getpeerucred GETPEERUCRED 'getpeerucred()'
   choose cl ipv6 IPV6 'IPv6 support' $socket_lib
   choose clr malloc0 MALLOC0 'non-NULL malloc(0)'
-  choose clr okwaitall OKWAITALL 'a usable MSG_WAITALL flag'
+  choose c msgdontwait MSGDONTWAIT 'MSG_DONTWAIT'
+  choose clr nbwaitall NBWAITALL 'non-blocking MSG_WAITALL'
   choose cl openat OPENAT 'openat()'
   choose cl linkat LINKAT 'linkat()'
   choose clr pipe2 PIPE2 'pipe2()'
diff --git a/src/libunixonacid/unixmessage_receive.c b/src/libunixonacid/unixmessage_receive.c
index 502b523..5c80082 100644
--- a/src/libunixonacid/unixmessage_receive.c
+++ b/src/libunixonacid/unixmessage_receive.c
@@ -14,19 +14,18 @@
 #include <skalibs/siovec.h>
 #include <skalibs/unixmessage.h>
 
-#ifdef SKALIBS_HASOKWAITALL
-# ifdef SKALIBS_HASCMSGCLOEXEC
-#  define RECV(fd, hdr) recvmsg(fd, (hdr), MSG_WAITALL | MSG_CMSG_CLOEXEC)
-# else
-#  define RECV(fd, hdr) recvmsg(fd, (hdr), MSG_WAITALL)
-# endif
+static int const awesomeflags =
+#ifdef SKALIBS_HASMSGDONTWAIT
+  MSG_WAITALL | MSG_DONTWAIT
+#elif defined (SKALIBS_HASNBWAITALL)
+  MSG_WAITALL
 #else
-# ifdef SKALIBS_HASCMSGCLOEXEC
-#  define RECV(fd, hdr) recvmsg(fd, (hdr), MSG_CMSG_CLOEXEC)
-# else
-#  define RECV(fd, hdr) recvmsg(fd, (hdr), 0)
-# endif
+  0
 #endif
+#ifdef SKALIBS_HASCMSGCLOEXEC
+  | MSG_CMSG_CLOEXEC
+#endif
+  ;
 
 static int unixmessage_receiver_fill (unixmessage_receiver_t *b)
 {
@@ -51,7 +50,7 @@ static int unixmessage_receiver_fill (unixmessage_receiver_t *b)
     cbuffer_wpeek(&b->mainb, v) ;
     iovec_from_siovec(iov, v, 2) ;
   }
-  r = RECV(b->fd, &msghdr) ;
+  r = recvmsg(b->fd, &msghdr, awesomeflags) ;
   if (r <= 0) return r ;
   {
     struct cmsghdr *c = CMSG_FIRSTHDR(&msghdr) ;
diff --git a/src/sysdeps/trymsgdontwait.c b/src/sysdeps/trymsgdontwait.c
new file mode 100644
index 0000000..0c8ad15
--- /dev/null
+++ b/src/sysdeps/trymsgdontwait.c
@@ -0,0 +1,17 @@
+/* ISC license. */
+
+#undef _POSIX_C_SOURCE
+#undef _XOPEN_SOURCE
+
+#ifndef _XPG4_2
+# define _XPG4_2
+#endif
+
+#ifndef _BSD_SOURCE
+#define _BSD_SOURCE
+#endif
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+int value = MSG_DONTWAIT ;
diff --git a/src/sysdeps/tryokwaitall.c b/src/sysdeps/trynbwaitall.c
index 15721b5..0f55080 100644
--- a/src/sysdeps/tryokwaitall.c
+++ b/src/sysdeps/trynbwaitall.c
@@ -53,8 +53,8 @@ static int child (int p, int fd)
   if (write(p, "", 1) < 1) return 111 ; /* sync with the parent */
   if (select(fd+1, &rfds, 0, 0, 0) < 1) return 111 ;
 
-  /* On buggy systems, the following recvmsg will block, despite
-     setting the fd non-blocking */
+  /* The following recvmsg may block, despite setting the fd
+     non-blocking. That is what we're testing. */
 
   if (recvmsg(fd, &msg, MSG_WAITALL) < 1) return 111 ;
   if (write(p, "", 1) < 1) return 111 ;