On Fri, Jun 01 2007, H. Peter Anvin wrote:
> > So there's a few things to take away from this:
> >
> > - regular file access MUST NOT return EAGAIN just because a page isn't
> > in the cache. Doing so is simply a bug. No ifs, buts or maybe's about
> > it!
> >
> > Busy-looping is NOT ACCEPTABLE!
> >
> > - you *could* make some alternative conventions:
> >
> > (a) you could make O_NONBLOCK mean that you'll at least
> > guarantee that you *start* the IO, and while you never return
> > EAGAIN, you migth validly return a _partial_ result!
> >
> > (b) variation on (a): it's ok to return EAGAIN if _you_ were the
> > one who started the IO during this particular time aroudn the
> > loop. But if you find a page that isn't up-to-date yet, and
> > you didn't start the IO, you *must* wait for it, so that you
> > end up returning EAGAIN atmost once! Exactly because
> > busy-looping is simply not acceptable behaviour!
>
> (b) seems really ugly. (a) is at least well-defined. Either seems
> wrong, though.
I totally agree, b) would get nasty. And while a) isn't perfect by any
means, I do follow Linus' logic and agree it's probably the best (only?)
way to handle it.
--
Jens Axboe
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