Re: [PATCH 5/9] block: introduce holder ops

[Christoph Hellwig <hch@lst.de>]

On Tue, May 16, 2023 at 07:36:26AM -0700, Darrick J. Wong wrote:
> > > +	mutex_lock(&bdev->bd_holder_lock);
> > >  	bdev->bd_holder = holder;
> > > +	bdev->bd_holder_ops = hops;
> > > +	mutex_unlock(&bdev->bd_holder_lock);
> > >  	bd_clear_claiming(whole, holder);
> > >  	mutex_unlock(&bdev_lock);
> > >  }
> > 
> > I guess the holder ops may be override in case of multiple claim, can
> > this be one problem from the holder ops user viewpoint? Or
> > warn_on_once(bdev->bd_holder_ops && bdev->bd_holder_ops != hops) is needed here?
> 
> <shrug> I'd have thought bd_may_claim would suffice for detecting
> multiple claims based on its "bd_holder != NULL" test?
> 
> Though I suppose an explicit test for bd_holder_ops != NULL would
> prevent multiple claims if all the claims had NULL holders.

bd_may_claim allows re-claims as long as the same holder is set.
I think we'll want to add an extra check that the holder_ops don't
change for this case.  They aren't with the current holders, but this
is a place where a belt and suspenders might be a good idea..

> 
> --D
> 
> > 
> > Thanks,
> > Ming
> > 
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