From: Neil Brown <neilb@suse.de>
Date: Mon, 5 Feb 2007 04:37:55 +0000 (+1100)
Subject: Make UDP sockets not blocking
X-Git-Tag: nfs-utils-1-0-11~17
X-Git-Url: https://git.decadent.org.uk/gitweb/?p=nfs-utils.git;a=commitdiff_plain;h=58e58ffbc0b12efbe00c9ad5f23d71d75790b524;hp=36959539fad2a5f125151a2e8bedb284d53b8c74

Make UDP sockets not blocking

 This is needs if mountd is running multithreaded else multiple threads
 will be blocked on a UDP port with nothing to read and so won't
 be able to serve up-calls from the kernel.

 Thanks to "Murali Krishna V" <vm.krishna@gmail.com> for highlighting
 the problem.
---

diff --git a/support/nfs/svc_socket.c b/support/nfs/svc_socket.c
index d712cab..3307600 100644
--- a/support/nfs/svc_socket.c
+++ b/support/nfs/svc_socket.c
@@ -113,11 +113,22 @@ svc_socket (u_long number, int type, int protocol, int reuse)
 	}
     }
 
-  if (sock >= 0 && protocol == IPPROTO_TCP)
+  if (sock >= 0)
     {
-	/* Make the TCP rendezvous socket non-block to avoid
-	 * problems with blocking in accept() after a spurious
-	 * wakeup from the kernel */
+	    /* This socket might be shared among multiple processes
+	     * if mountd is run multi-threaded.  So it is safest to
+	     * make it non-blocking, else all threads might wake
+	     * one will get the data, and the others will block
+	     * indefinitely.
+	     * In all cases, transaction on this socket are atomic
+	     * (accept for TCP, packet-read and packet-write for UDP)
+	     * so O_NONBLOCK will not confuse unprepared code causing
+	     * it to corrupt messages.
+	     * It generally safest to have O_NONBLOCK when doing an accept
+	     * as if we get a RST after the SYN and before accept runs,
+	     * we can block despite being told there was an acceptable
+	     * connection.
+	     */
 	int flags;
 	if ((flags = fcntl(sock, F_GETFL)) < 0)
 	  {