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

From: Alan Stern
Date: Wed May 27 2009 - 14:16:49 EST

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

> Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes:
> > On Wed, 27 May 2009, Kay Sievers wrote:
> >
> >> On Wed, May 27, 2009 at 01:49, James Bottomley
> >> <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> 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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