Re: [PATCH 0/23] File descriptor hot-unplug support v2

From: Miklos Szeredi
Date: Tue Jun 09 2009 - 01:51:16 EST

On Mon, 8 Jun 2009, Al Viro wrote:
> On Mon, Jun 08, 2009 at 06:44:41PM +0200, Miklos Szeredi wrote:
> > I'm still not getting what the problem is. AFAICS file operations are
> > either
> >
> > a) non-interruptible but finish within a short time or
> > b) may block indefinitely but are interruptible (or at least killable).
> >
> > Anything else is already problematic, resulting in processes "stuck in
> > D state".
> Welcome to reality...
> * bread() is non-interruptible
> * so's copy_from_user()/copy_to_user()

And why should revoke(2) care? Just wait for the damn thing to
finish. Why exactly do these need to be interruptible?

Okay, if we want revoke or umount -f to be instantaneous then all that
needs to be taken care of. But does it *need* to be?

My idea of revoke is something like below:

- make sure no new operations are started on the file
- check state of tasks for ongoing operations, if interruptible send signal
- wait for all pending operations to finish
- kill file

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