linux-kernel - Re: [PATCH 1/2] md: make devices disappear when they are no longer needed.

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Message-ID: <20081124063806.GA28946@ZenIV.linux.org.uk>
Date:	Mon, 24 Nov 2008 06:38:06 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Neil Brown <neilb@...e.de>
Cc:	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	Tejun Heo <tj@...nel.org>, Doug Ledford <dledford@...hat.com>
Subject: Re: [PATCH 1/2] md: make devices disappear when they are no longer
	needed.

On Mon, Nov 24, 2008 at 03:47:51PM +1100, Neil Brown wrote:

> > What lifetime rules do you really want?  I never liked the tricks pulled
> > by md wrt gendisk lifetimes and that might be a good time to sort that
> > out for good...
> 
> I'm not sure what 'tricks' you are referring to.  Can you elaborate?
> 
> I want the gendisk to appear as soon as it is needed (not because I
> think that is necessarily a good idea, but it is legacy functionality that I
> don't think we can easily discard).  And I want them to disappear when
> they contain no information and have nothing referring to them.

"Tricks" are about md_probe() and weird allocation time for these suckers.
But OK, legacy API is a good argument.

So you want the rules of the same nature as for module refcount?  Then
the natural place to do that would be in failure exit of __blkdev_get()
and in normal path in blkdev_put() (for the final opener going away).

However, let's try to do it right - there's a *lot* of drivers where
we do no work in ->release() until it's the final one.  It would be
nice to accomodate them as well while we are at it...
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