[stgt] STGT fork for "broken disk emulation"

[ronnie sahlberg]

On Wed, Jul 23, 2014 at 7:50 AM, FUJITA Tomonori
<fujita.tomonori at lab.ntt.co.jp> wrote:
> On Tue, 22 Jul 2014 16:23:54 +1000
> Mark Harvey <markh794 at gmail.com> wrote:
>
>> Could this be simply a new backing store type ?
>
> Sounds reasonable to me. If we could inject an error dynamically, it
> would be useful, I think.

Thanks. That is useful to know.

I will refactor the code and move the error injection into a new
backing store instead.  bs_errorinject.c or something.

Only drawback wiht a backing store I think would be that you can not
test non-medium access CDBs from it, nor can we error inject on the
iscsi layer.
That said, I do not know if that would be all that useful anyway.
At this stage I am mainly interested in trying to create a disk with
failing medium so that we can test scsi initiators and filesystem
error recovery paths to make both
easier to test and more robust against medium failures.

This all depends on if I can reach a stage where people like file
system developers, raid driver developers etc, will find it useful and
will want to use it.


regards
ronnie sahlberg


>
>> Depends on error injection you want/need. If it is scsi command related, should be achievable in backing store. If it's transport related then I could see it being more invasive.
>>
>> Another idea would be to hijack send/receive diagnostic op code. Initiator could send "injection commands" via receive diag op code payload & check status etc via send diag
>>
>> Sent from my iPhone
>>
>>> On 22 Jul 2014, at 7:52, ronnie sahlberg <ronniesahlberg at gmail.com> wrote:
>>>
>>> List,
>>>
>>> I have created a temporary work version of TGTD at:
>>> https://github.com/rsahlberg/flaky-stgt
>>>
>>> This is not a production TGTD or a version that any normal users should use,
>>> instead I had an idea to try to add features to make it possible to create an
>>> iSCSI device that is broken and misbehaves in controllable ways.
>>>
>>> For example, imagine a scsi disk that is "good" right now but after a
>>> certain stage in a scripted test the disk goes bad and start failing
>>> all WRITE commands.
>>> Just like a disk that suddenly has run out of reallocation space.
>>>
>>>
>>> The only people I see that could find this type of feature useful
>>> would be, I guess,
>>> filesystem developers, SCSI initiator midlayer developers or perhaps
>>> people writing
>>> code that talks directly to the disk and want to test that their error
>>> recovery paths
>>> work.
>>> I see no use or benefit from these features to normal users.
>>>
>>>
>>> Right now it is a bit in flux, and I also need to see if I can find
>>> buy-in and convince
>>> filesystem and block device driver developer folks that this could
>>> actually be useful to them.
>>>
>>> Later on would come the question, should I refactor the code and
>>> should we push this into STGT mainline?
>>> I personally think that this usecase I am aiming for is so special
>>> case, and is only
>>> features that are useful or relevant to an almost infinitely small set
>>> of filesystem and block device driver developers that it would not
>>> make much sense.
>>> But if the TGTD community would rather have this built-in to official TGTD I am
>>> more than happy to rework the patches once things stabilize and submit.
>>>
>>> This is not a hostile fork. this is a temporary work/scratch space
>>> while I experiment
>>> on "broken disk emulation" and while I try to see if there is interest
>>> in the devlopment community of this as a test tool.
>>>
>>>
>>> If anyone of you think this could be useful, please feel to try it out
>>> or let your
>>> filesystem developer friends know that "could you use a scsi disk that
>>> is 'busted' in controllable ways for your testing?"
>>>
>>>
>>> best regards
>>> ronnie sahlberg
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