MEDIUM: listener: provide a fallback for accept4() when not supported

It happens that on some systems, the libc is recent enough to permit
building with accept4() but the kernel does not support it. The result
is then a disaster since no connection is accepted. We now detect this
and automatically fall back to accept() and fcntl() when this happens.

diff --git a/src/listener.c b/src/listener.c
index c4259bcd5a1bf56f0de53093baf7c85a4bf5e9ea..6781e587cd5b61efed5e9a1142988c3121a0cf5e 100644 (file)
--- a/src/listener.c
+++ b/src/listener.c
@@ -311,6 +311,11 @@ void listener_accept(int fd)
 
 #ifdef USE_ACCEPT4
                cfd = accept4(fd, (struct sockaddr *)&addr, &laddr, SOCK_NONBLOCK);
+               if (unlikely(cfd == -1 && errno == EINVAL)) {
+                       /* unsupported syscall, fallback to normal accept()+fcntl() */
+                       if ((cfd = accept(fd, (struct sockaddr *)&addr, &laddr)) != -1)
+                               fcntl(cfd, F_SETFL, O_NONBLOCK);
+               }
 #else
                cfd = accept(fd, (struct sockaddr *)&addr, &laddr);
 #endif