Re: [PATCH] coda: kill file_count abuse

[David Chinner <dgc@sgi.com>]

On Fri, Jul 20, 2007 at 01:53:16AM +0100, Al Viro wrote:
> On Fri, Jul 20, 2007 at 10:45:34AM +1000, David Chinner wrote:
> > On Thu, Jul 19, 2007 at 06:16:00PM -0400, Jan Harkes wrote:
> > > On Thu, Jul 19, 2007 at 11:45:08PM +0200, Christoph Hellwig wrote:
> > > > ->release is the proper way to detect the last close of a file,
> > > > file_count should never be used in filesystems.
> > > 
> > > Has been tried, the problem with that once ->release is called it is too
> > > late to pass the the error back to close(2).
> > 
> > I think you'll find the problem is that fput() throws away the error
> > from ->release, not that it's too late....
> 
> Just where would that return value go?

To the context that dropped the last reference. It can't be
reported to anything else....

I'd much prefer to get an error on a file to any process
that was using the file than have a potential indication of
data or filesystem corruption silently dropped in the
bit bucket.....

> BTW, the reason why checks for struct file refcount blow is not far
> from that:
> 
> task A: write()
> task B (sharing descriptor table with A): close()
> task C (with another reference to struct file in question): close()
> task A: return from write()
> 
> Now, the final fput() here happens in write().  In particular, no
> call of close(2) sees refcount equal to 1.

Sure, but you've given no reason why the write() is unable to
or should not return the error.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group