race conditions in udevd

[Chris Friesen <chris_friesen@sympatico.ca>]

I just realized that we've got some gaping flaws in the udevd signal 
handler logic.

Currently the actual signal handler sets various flags.  We then wait 
for an incoming message and handle it, then check the flags to see if we 
need to do various things..

The problem is, if we get SIGALRM or SIGCHLD before we get back to 
recvmsg(), we'll wait there until the next message comes in--which could 
be quite a while.  Sorry guys, I screwed up in my original patch, and it 
took until now to see it.

The fix is straightforward.  In the init code we create a pipe.  In the 
signal handler we write a byte (based on what signal came in) to the 
pipe. We add a select() in the main loop that listens on the pipe and on 
the unix socket.  When the unix socket is readable, we run the existing 
recvmsg() code.  When the pipe is readable, we read the byte and run the 
appropriate code.

I don't have time to send a patch tonight, but will do so in the next 
few days if nobody beats me to it.

Chris



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