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1.3.19-1:poll bug. Patch included.


While working on another program (syslogd in inetutils) I found that the poll function was returning POLLERR when something arrived on a UDP socket; it should be return POLLIN. Inside the poll function, recvfrom was returning -1 with errno = EMSGSIZE, but the only error value being check for in WSAENOTCONN. However EMSGSIZE is a reasonable return value since the buffer to recvfrom was only 1 byte while the actual message size was larger than this. Basically saying your buffer is too small for the message, but since we are only peeking, this shouldn't be returned as a POLLERR.

The fix should be to add EMSGSIZE as part of the condition so this error returns POLLIN. I'm including the patch below and a changelog following that. Please review these changes and make sure that they seem reasonable. I've done tests on my system (windows XP) and have verified that the change works.

Index: winsup/cygwin/
RCS file: /cvs/src/src/winsup/cygwin/,v
retrieving revision 1.34
diff -u -p -r1.34
--- winsup/cygwin/ 20 Nov 2002 11:00:15 -0000 1.34
+++ winsup/cygwin/ 3 Feb 2003 01:52:10 -0000
@@ -112,7 +112,8 @@ poll (struct pollfd *fds, unsigned int n
sense then. It returns WSAENOTCONN in that
case. Since that's not actually an error,
we must not set POLLERR but POLLIN. */
- if (WSAGetLastError () != WSAENOTCONN)
+ if (WSAGetLastError () != WSAENOTCONN &&
+ errno!=EMSGSIZE)
fds[i].revents |= POLLERR;
fds[i].revents |= POLLIN;
2003-02-02 Peter Rehley<>

* EMSGSIZE being ignore returning incorrect POLLERR on UDP socket receive
if recvfrom returns error, return POLLIN if errno = EMSGSIZE

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