linux-kernel - Re: [SCSI] fix media change events for polled devices

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Date:	Fri, 21 Mar 2008 14:44:22 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-scsi@...r.kernel.org
Subject: Re: [SCSI] fix media change events for polled devices

On Fri, 2008-03-21 at 13:12 -0400, Jeff Garzik wrote:
> Linux Kernel Mailing List wrote:
> >     [SCSI] fix media change events for polled devices
> >     
> >     Commit:
> >       a341cd0f (SCSI: add asynchronous event notification API)
> >     breaks:
> >       285e9670 (sr,sd: send media state change modification events)
> >     by introducing an event filter, which is removed here, to make
> >     events, we are depending on, happen again.
> 
> 
> By simply reading the code history, it is trivial to verify that this 
> description is false:
> 
> Commit 285e9670 depends on a341cd0f, so by definition it is 285e9670 -- 
> or rather the incomplete update of your original patch that resulted in 
> 285e9670 -- that is broken.
> 
> Since commit 285e9670 is broken, you fixed the wrong thing.
> 
> Furthermore, you broke a userspace interface that was introduced by 
> a341cd0f, by removing the event filter controlled by userspace.

> Did anyone bother to read any code at all?

Yes, I did.  The userspace interface has never worked as a writeable
attribute because it's read only (as Kay has pointed out several times).
Based on that, I just #if'd out the filter code to get polled media
events working again.

The filter can be put back with a better discriminator for 2.6.26

> When 285e9670 was updated for the scsi_evt_* interface, it should have 
> initialized the supported_events mask.

That would break HAL ... it's using the presence of the media_event flag
in the variable to indicate it doesn't need to poll.  We need two flags,
one for polling and one for AN.

> And that is the fix -- initialize supported_events according to sr/sd's 
> needs, and revert this change (4d1566ed2100d074ccc654e5cf2e44cdea3a01d0) 
> as obviously broken.

James


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