Originally Posted by mr_bandit

To be honest, I did not look at errno after msgget() returned 0 (It was in the wee early hours and I had bigger fish..). I will try that and get back with the results. This will also tell me if the original key returns 0.

The interesting thing is we loaded a *way* earlier version of the code to test a completely different thing. I jut did a ipcs and got

Code:

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages
0x000000f0 0          gfi        666        0            0

where you can see msgqid == 0 and the system seems to be performing happily (at least this part of it). This would seem to enforce the observation / theory that once the msgqid becomes 0, it stays 0. No complaints from msgsnd() or msgrcv().

So - this may be a brainfart on my part. After all, I did have another bug throwing a SIGSEGV at the same time. And it was very late/early. If it is a brainfart, my apologies.

Again, this an unpatched Ubuntu 8

@achenlehas an interesting suggestion. I had not thought of setting errno to a value before making the call. The question then becomes: why not set it to (-1)? errno values are positive, at least on Linux. (I seem to remember them being negative numbers on BSD 4.1, but that was a *long* time ago...)

This function shall not change the setting of errno if successful.

Since some value is returned on error and is also a valid return on
success, an application wishing to check for error situations should
set errno to 0, then call function(), then check errno.