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

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Date:	Wed, 27 May 2009 14:15:42 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Kay Sievers <kay.sievers@...y.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	SCSI development list <linux-scsi@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	<linux-fsdevel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs  directories.

On Wed, 27 May 2009, Eric W. Biederman wrote:

> Alan Stern <stern@...land.harvard.edu> writes:
> 
> > On Wed, 27 May 2009, Kay Sievers wrote:
> >
> >> On Wed, May 27, 2009 at 01:49, James Bottomley
> >> <James.Bottomley@...senpartnership.com> wrote:
> >> 
> >> > OK ... perhaps we have to wait a little harder: try this; it waits until
> >> > all the targets have disappeared from visibility via an event.
> >> 
> >> That seems to work fine here.
> >
> > It's good for a short-term fix.  For the longer term, I still think 
> > it's a mistake to wait for the sdevs to be released before deleting the 
> > target.  It gives user programs the ability to block the host-removal 
> > thread indefinitely.
> 
> How can user programs block removal indefinitely today?

As fas as I know, they can't.  Instead, they can cause the SCSI layer 
to unregister a sysfs directory containing a child directory.  :-)

Basically, a user program can delay removal of the child (i.e., the
target) directory indefinitely, because currently the target isn't
unregistered when all its children are removed -- it's unregistered
when all its children are _released_.

Alan Stern

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