Re: libata hotplug question

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2009-12-01 at 13:51 +0900, Tejun Heo wrote:
> 
> If the hotplug events are completely reliable, we can add a flag to
> tell libata EH to trust the hotplug notices completely but then again
> I'm not too convinced about the benefits of implementing it in very
> small number of drivers.  It could be more beneficial to keep the
> behavior consistent across all ATA drivers.

Well... in my case I know for sure the device is out. So the stuff
libata does to try to poke at the device is not only a waste of time,
but a few scary messages in the dmesg log ;-)

> It's basically an advisory flag telling libata to try to look for new
> devices.  From outside EH, the only behavior difference is that with
> the flag set EH will try to re-enable ports which got disabled due to
> repeated reset failures.

Ok, but ata_ehi_hotplugged() will set it anyway so I don't really have
to do anything.

> > At the end of the day, it might be better to just add those link
> > callbacks... I'll give that a try too, unless you have a better
> idea.
> 
> Link callbacks won't change the hotplug behavior tho.

Right, see my other message, they make the situation even more complex
in fact so I'm backing off that.

> Oh yeah, link stuff will help that.  Or you can also implement custom
> softreset which checks link status and exits early if there's no
> device.

That might be an option, I'll look at it.

> The only problem with the latter approach is that you'll need
> to take care of the race window in the driver itself.  You can close
> the window by checking link status again in postreset and rescheduling
> hotplug event if hotplug event happened after the link state is
> checked in softreset but before the port was thawed.

I've done simpler. I've added a pair of calls to lock/unlock the media
bay which directly grab the bay driver internal mutex, which guarantees
we won't get any callback while we hold it. I could have done something
like you described instead but this is easy and allow to also easily
solve some of the possible races with drivers/ide while at it.

> Those events are all advisory.  The final decision is always upto what
> the reset methods and following probes tell the EH, so it may go
> through one more EH round but it won't lose anything.

That's what I'm starting to understand :-) Very good. I'll look at the
custom softreset approach.

Cheers,
Ben.