Re: fanotify as syscalls

Linus Torvalds
2009-09-17T16:40:51Z

On Wed, 16 Sep 2009, Jamie Lokier wrote:
>
> I'd forgotten about Linus' strace argument. That's a good one.
>
> Of course everything should be a syscall by that argument :-)

Oh yes, everything _should_ be a syscall.

The problem is that many things are too "amorphous" to be system calls,
and don't have any sane generic semantics (ie they only act on a specific
device node). So we have ioctl's etc for those things.

And then we have page faults. I've long wished that from a system call
tracing standpoint we could show page faults as pseudo-system-calls (at
least as long as they happen from user space - trying to handle nesting is
not worth it). It would make it _so_ much more obvious what the
performance patterns are if you could just do

strace -ttT firefox

for the cold-cache case and you'd see where the time is really spent.

(yeah, yeah, you can get that kind of information other ways, but it's a
hell of a lot less convenient than just getting a nice trace with
timestamps).

> And strace can trace some ioctls and setsockopts. (But it's never
> pretty to see isatty() showing in strace as SNDCTL_TMR_TIMEBASE :-)

Yes, strace can fix things up, and show "send a packet" as "fanotify". But
it's nasty and hard.

Quite frankly, I have _never_ever_ seen a good reason for talking to the
kernel with some idiotic packet interface. It's just a fancy way to do
ioctl's, and everybody knows that ioctl's are bad and evil. Why are fancy
packet interfaces suddenly much better?

Linus