Re: [PATCH] scsi: sd: block: Handle cases where devices come online read-only

[Hannes Reinecke <hare@suse.de>]

On 2/12/19 9:03 AM, Christoph Hellwig wrote:
> On Fri, Feb 08, 2019 at 06:38:31PM -0500, Martin K. Petersen wrote:
>> Some devices come online in write protected state and switch to
>> read-write once they are ready to process I/O requests.
> 
> That is really weird.  What kind of devices are these?
> 
No, not really.
Some arrays (HP IIRC) use a similar mechanism for volume copy or snapshots.

>> Note that per-partition ro settings are lost on revalidate. This has
>> been broken for at least a decade and it will require major surgery to
>> fix. To my knowledge nobody has complained about being unable to make
>> partition read-only settings stick through a revalidate. So hopefully
>> this patch will suffice as a simple fix for stable.
> 
> Should we warn when we lost these settings on a revalidate?
> 
> I have to say I don't like the tristate too much - it seems to allow
> setting a hardware write protected device writable again by user
> interfaction, right?
> 
> Should we just have a hardware and a user policy field that are separate
> instead?
> 
Problem is how the mechanism should work.
Thing is, once a device goes read-only we pretty much stop accessing it 
(as it will send any filesystem down onto the recovery path).
And once we stop sending I/O to it we'll lose the ability to figure out 
that the device switched back to R/W mode.

(Always assuming that we'll be getting a sense code in the first place).

But overall I have to agree with Christoph.
Read-only devices and the handling of which is pretty much 
array-specific, so I doubt we can generalize much here.

Cheers,

Hannes
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Dr. Hannes Reinecke		   Teamlead Storage & Networking
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