Re: [PATCH v3 07/18] scsi: sd: detect support for command duration limits

Damien Le Moal
2023-01-29T02:05:40Z

On 1/28/23 11:52, Bart Van Assche wrote:
> On 1/27/23 16:51, Damien Le Moal wrote:
>> On 1/27/23 22:00, Hannes Reinecke wrote:
>>> Hmm. Calling this during revalidate() makes sense, but how can we ensure
>>> that we call revalidate() when the user issues a MODE_SELECT command?
>>
>> Given that CDLs can be changed with a passthrough command, I do not think we can
>> do anything about that, unfortunately. But I think the same is true of many
>> things like that. E.g. "let's turn onf/off the write cache without the kernel
>> noticing"... But given that on a normal system only privileged applications can
>> do passthrough, if that happens, then the system has been hacked or the user is
>> shooting himself in the foot.
>>
>> cdl-tools project (cdladm utility) uses passtrhough but triggers a revalidate
>> after changing CDLs to make sure sysfs stays in sync.
>>
>> As Christoph suggested, we could change all this to an ioctl(GET_CDL) for
>> applications... But sysfs is so much simpler in my opinion, not to mention that
>> it allows access to the information for any application written in a language
>> that does not have ioctl() or an equivalent.
>>
>> cdl-tools has a test suite all written in bash scripts thanks to the sysfs
>> interface :)
>
> My understanding is that combining the sd driver with SCSI pass-through
> is not supported and also that there are no plans to support this
> combination.

Yes. Correct. Passthrough commands do not use sd. That is why cdl-tools triggers
a revalidate once it is done with changing the CDL descriptors using passthrough
commands.

>
> Martin, please correct me if I got this wrong.
>
> Thanks,
>
> Bart.
>

--
Damien Le Moal
Western Digital Research