Re: hot plug on ICH9 with AHCI on

[Tejun Heo <tj@kernel.org>]

Hello,

Владимир Дашевский wrote:
>> Not all EMIs are one-shot events.  Some can span seconds.  Links don't
>> always come up right after failures.  Sometimes they require more than
>> one hardresets to get back to working order.  Link status report is
>> not reliable.  Sometimes they report offline for a while after certain
>> events.  If you know how to work around the above problems under a
>> second, I'm all ears but I doubt it unless it involves an additional
>> mechanical switch.
>>   
> Well, for example, USB devices have a pull-up resistor on their D+ line.
> DC bias can be used for detection of device presence without mechanical
> switch.

SATA is not USB and onlineness detection isn't that simple.  Also,
have you tried to run a system on a USB device over flaky connection?

>> The echo to delete node is synchronous.  It will return after the
>> device is completely removed but please note that "removing" in this
>> sense only covers the device itself.  It will flush the request queue
>> and spin the drive down but won't do anything about filesystems.  You
>> need to unmount first.  hal and desktop stuff already do the right
>> thing for devices marked removable.
>>   
> Ok, but two more questions:
> 1. Is there any generic mechanism of notifiing processes which had
> previously opened device being deleted of this event? What will happen
> to such processes? Is it possible to check who are those who uses the
> drive at the moment?

-EIO will happen, fuser, but if you want something intelligent, hal +
dbus.

> 2. If the drive was deleted is it possible to start it back without
> physical re-connection? Can I simulate status change og that port to
> force the driver to auto-detect block device?

I don't really follow what you're trying to achieve but if you want
some fancy snapshotting + remapping trick, the best place would be dm.

> PS: as for this:
>> I'll be happy to improve EH behavior but you need to come up with
>> better reasons.
>>   
> I can tell that for me enclosure management support is quite a good
> reason.

How is that in any way exclusive against longer detach delay?

> Unfortunately, there is no this support in official kernel. I have
> seen only limited support of activity LED in kernel 2.6.28.
> However, I am using Debian where the latest kernel is only
> 2.6.26. As a result I had to write a simple ahci_em module which
> register simple proc interface to send LED states to all ICH9
> ports. However, final goal is to integrate this module with mdadm to
> have proper indication of RAID state.

The biggest obstacle is that there aren't too many enclosure devices
floating around.  What kind of device are you using?

-- 
tejun