Re: fgetattr/fsetattr file operation

[Jamie Lokier <jamie@shareable.org>]

Miklos Szeredi wrote:
> On Thu, 4 Jun 2009, Brian Molnar wrote:
> > > On Thu, Jun 4, 2009 at 12:04 PM, Andreas Dilger <adilger@sun.com> wrote:
> > > This sounds very strange - different processes (or even the same
> > > process using different file handles) will see different results
> > > for fstat() which are yet different from stat().  I can't imagine
> > > that applications would like this at all.
> > 
> > Ya, no doubt a good deal of applications would get very confused if
> > they didn't know the difference. And it is not the goal of this FS to
> > support the use of general applications.
> 
> Actually, well written applications shouldn't assume that
> fd=open(path);fstat(fd) is equivalent to fd=open(path);stat(path).
> Why?  Because the second one is racy wrt. remove and rename.

No, but well written applications can and do assume this:

    st1=stat(path)

    ...time passes, maybe do some filesystem operations, talk on the network...

    fd=open(path)
    st2=fstat(fd)

    if (st1!=st2)
        abort or loop "Race happened, something changed under me..."

-- Jamie
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