Re: fibre channel sync cache question

[Michael Reed <mdr@sgi.com>]

Douglas Gilbert wrote:
> Arjan van de Ven wrote:
>> On Tue, 2006-07-25 at 16:28 -0600, Moore, Eric wrote:
>>> -- Tuesday, July 25, 2006 4:22 PM, Michael Reed wrote:
>>>> Using fibre channel disks, I've noticed that when the system shuts down
>>>> that the sd_driver issues a sync cache command to the device.  I've
>>>> also
>>>> noticed that when the lldd is removed via rmmod that this sync cache is
>>>> not executed.  I would think that the sync cache would be desirable
>>>> under this circumstance.
>>>>
>>> This is not handled from sg path as well.  Meaning if you
>>> use sdparm, and enable the caching page WCE bit, then reboot,
>>> there is no SYNC cache issued from above.
>>> We handle this in fusion drivers due to short coming from above.
>>
>>
>> Hi,
>>
>> that sounds sooo like the wrong approach... wouldn't it be better to fix
>> sg instead?
> 
> Uh? sg is just a pass through. As such it can subvert
> policy decisions of the kernel. That isn't always a
> bad thing :-)
> 
> The design flaw is any driver that tries to maintain a
> state variable associated with a device (logical unit)
> and can't cope with situations when it gets out of sync.
> If you managed to neuter the pass through, how would you
> cope with another initiator?

Perhaps the best policy for sd is to assume that WCE is enabled
and just issue the sync cache.

--

I'm wondering about the policy of issuing a sync cache.  There
are target removal paths which result in it not being issued.

So, the real question is: when a scsi target is removed, is it
policy that sync cache will be issued?

In fibre channel, here are two code paths in which sync cache
is not issued.

	- removal of LLDD (rmmod)
	- removal of target via sysfs device/delete

In a closer look at the target removal via sysfs device/delete,
I observe that portions of the sysfs fc_remote_ports/rport-*
remain in place.

Do we need to tie the device/delete to the transport?

Can of worms?  Close eyes, run screaming?

Mike


> 
> Doug Gilbert
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