This is a silly question, but,
Is there anyway to do read/write on the same file without
the kernel lock? Thanks!
On Fri, 12 May 2000, Alfred Perlstein wrote:
> * Sergey Babkin <[EMAIL PROTECTED]> [000512 15:23] wrote:
> > Alfred Perlstein wrote:
> > >
> > > * Ville-Pertti Keinonen <[EMAIL PROTECTED]> [000511 22:49] wrote:
> > > >
> > > > [EMAIL PROTECTED] (FengYue) writes:
> > > >
> > > > > loop. Now, the third program reads 4K of data from /tmp/pagetest
> > > > > and exit if the 4K data does not contain all 'A's nor 'Z's. 3 programs
> > > > > run concurrently on the same machine (3.4). No lock in the code whatsoever,
> > > >
> > > > Not quite. If FreeBSD didn't perform locking, operations affecting
> > > > single filesystem blocks would probably be atomic (as long as the
> > > > userland buffer is in memory).
> > > >
> > > > However, FreeBSD does perform locking in read(2) and write(2) for
> > > > local files, so your third program should never fail and exit.
> > > >
> > > > Note that the system call interface does not guarantee reads or writes
> > > > to be atomic, this just happens to be how it is implemented at the
> > > > moment.
> > >
> > > Afaik several Unix standards mandate this behavior, Linux doesn't
> > > follow this standard though.
> >
> > Sounds like one more of these subtle weirdnesses in Linux that
> > annoy me so much :-(
>
> This weirdness is intentional, it's a shortcut for speed taken at
> the expense of real unix compatibility.
>
> > Solaris seems to be another example a system with not quite atomic
> > writes. The writes themselves seem to be atomic but in append mode the
> > positioning at the end of file is not atomic with writes. So when
> > appending to a log file from multiple sources the messages tend to
> > overlap (be written at the same position).
>
> That's why I use FreeBSD, it works. :)
>
> --
> -Alfred Perlstein - [[EMAIL PROTECTED]|[EMAIL PROTECTED]]
> "I have the heart of a child; I keep it in a jar on my desk."
>
>
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