|| ||Linus Torvalds <torvalds-AT-linux-foundation.org> |
|| ||Jamie Lokier <jamie-AT-shareable.org> |
|| ||Re: fanotify as syscalls |
|| ||Thu, 17 Sep 2009 09:40:16 -0700 (PDT)|
|| ||Evgeniy Polyakov <zbr-AT-ioremap.net>, Eric Paris <eparis-AT-redhat.com>,
David Miller <davem-AT-davemloft.net>,
|| ||Article, Thread
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
> 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?
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