Re: clone() <-> getpid() bug in 2.6?

Linus Torvalds
2004-06-06T06:07:48Z

On Sun, 6 Jun 2004, Kalin KOZHUHAROV wrote:
>
> Well, not exactly sure about my reply, but let me try.
>
> The other day I was debugging some config problems with my qmail instalation and I ended up doing:
> # strace -p 4563 -f -F
> ...
> [pid 13097] read(3, "\347\374\375TBH~\342\233\337\220\302l\220\317\237\37\25"..., 32) = 32
> [pid 13097] close(3) = 0
> [pid 13097] getpid() = 13097
> [pid 13097] getpid() = 13097
> [pid 13097] getuid32() = 89
> [pid 13097] getpid() = 13097
> [pid 13097] time(NULL) = 1086497450
> [pid 13097] getpid() = 13097
> [pid 13097] getpid() = 13097
> [pid 13097] getpid() = 13097

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