Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs directories.

[Alan Stern]

On Wed, 27 May 2009, James Bottomley wrote:

> Hardly ... our current refcounting is on destruction (releases).  This
> problem is an instance of visibility (the del calls) we need the
> visibility teardown to work nicely.  We currently have no refcounting on
> the visibility.  Even if we did (and we could add a ref on when the
> underlying device del calls are done), what happens if the target needs
> to become visible again.  Apparently the generic device infrastructure
> can't accept doing an add on a previously del'd device.

Definitely not.

> The most obvious way of fixing this is to have a special case for
> targets of dying hosts ... they could call del early on the
> understanding that they're never getting new underlying devices.  That
> would allow the wait to trigger on the last target del, which is what is
> optimal.

I don't understand all the subtle issues here.  In other contexts, the 
solution would be to initialize a refcount to 1 when the target is 
allocated, increment it when a device is added, and decrement it when a 
device is removed or the host is removed.  When the refcount goes to 0, 
the target is deleted.  Why wouldn't this kind of approach work?

Alan Stern

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