Linus on qmail

Posted by Amit Shah on June 07, 2004

A thread's going on on LKML about a glibc bug that caches the value of getpid(), which breaks programs that create threads. Someone then reported qmail doing several getpid()s. Here's Linus' reply:

qmail is a piece of crap. The source code is completely unreadable, and it seems to think that "getpid()" is a good source of random data. Don't ask me why.

It literally does things like

random = now() + (getpid() << 16);

and since there isn't a single comment in the whole source tree, it's pointless to wonder why. (In case you wonder, "now()" just does a "time(NULL)" call - whee.).

I don't understand why people bother with it. It's not like Dan Bernstein is so charming that it makes up for the deficiencies of his programs.

But no, even despite the strange usage, this isn't a performance issue. qmail will call "getpid()" a few tens of times per connection because of the wonderful quality of randomness it provides, or something.

This is another gem you find when grepping for "getpid()" in qmail, and apparently the source of most of them:

if (now() - when < ((60 + (getpid() & 31)) << 6))

Don't you love it how timeouts etc seem to be based on random values that are calculated off the lower 5 bits of the process ID? And don't you find the above (totally uncommented) line just a thing of beauty and clarity?

Yeah.

Anyway, you did find something that used more than a handful of getpid() calls, but no, it doesn't qualify as performance-critical, and even despite it's peyote-induced (or hey, some people are just crazy on their own) getpid() usage, it's not a reason to have a buggy glibc.

Linus