Re: [PATCH v8 10/11] scsi: sr: support (un)block events

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On Mon, 29 Oct 2012, James Bottomley wrote:

> On Mon, 2012-10-29 at 17:01 +0800, Aaron Lu wrote:
> > 2 interfaces are added to block/unblock events for the disk sr manages.
> > This is used by SATA ZPODD, when ODD is runtime powered off, the events
> > poll is no longer needed so better be blocked. And once powered on,
> > events poll will be unblocked.
> > 
> > These 2 interfaces are needed here because SATA layer does not have
> > access to the gendisk structure sr manages.
> 
> I'm afraid this is a nasty layering violation.  You can't have a low
> level driver have knowledge of a call back in an upper layer one (in
> this case sr_block_events).
> 
> This is all done it looks like because of the problem of getting access
> to the scsi_cd structure from libata, but it's not the right way to
> solve it.
> 
> I also don't really think you need to do any blocking or unblocking.  As
> I said in the previous thread, just fake the events the standard tells
> you to, so userspace can probe to its heart's content and you can keep
> the device powered off.

James, one of us has misunderstood the event-polling mechanism.  As far
as I know, the polling calls that Aaron is concerned with are generated
by the kernel, not by userspace.

Alan Stern

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