Date:	Wed, 27 Aug 2014 10:48:16 -0400
From:	Douglas Gilbert <dgilbert@...erlog.com>
To:	Hannes Reinecke <hare@...e.de>,
	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
CC:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, yrl.pp-manager.tt@...achi.com,
	linux-kernel@...r.kernel.org,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH -logging 00/10] scsi/constants: Output continuous
 error messages on trace

On 14-08-27 10:23 AM, Hannes Reinecke wrote:
> On 08/08/2014 03:07 PM, Douglas Gilbert wrote:
>> On 14-08-08 01:50 PM, Yoshihiro YUNOMAE wrote:
>>> Hi All,
>>>
>>> This patch set introduces new traceevents in order to output
>>> continuous error
>>> messages. Current SCSI printk messages in upstream kernel can be
>>> divided by and
>>> mixed with other messages. Even if each error message has its
>>> device id,
>>> sometimes we can easily be lost in mixed logs because the
>>> message's device id
>>> is separated from it's body. To avoid it, I'd like to use
>>> traceevents to
>>> store error messages into the ftrace or perf buuffer, because
>>> traceevents
>>> are atomically commited to the buffer.
>>>
>>> In this patch set, all printk messages are removed based on a local
>>> discussion with Hannes, but I think printk messages should be kept
>>> because all
>>> users don't enable traceevents and rsyslog can store as files.
>>>
>>> However, if printk of logging branch is kept, the messages are
>>> duplicate and
>>> it can induce stack overflow by using local buffer(*1).
>>>
>>>   (*1) https://lkml.org/lkml/2014/5/20/742
>>>
>>> So, my suggestion is follows:
>>>
>>> 1) printk
>>> Keeps current implemntation of upstream kernel.
>>> The messages are divided and can be mixed, but all users can check
>>> the error
>>> messages without any settings.
>>>
>>> 2) traceevents
>>> To get the complete messages, we can use ftrace or perf (or
>>> something on them).
>>> Users can always understand correct messages, but they need to set
>>> up the
>>> tracers.
>>>
>>> This patch set is based on Hannes' logging branch:
>>> http://git.kernel.org/cgit/linux/kernel/git/hare/scsi-devel.git/log/?h=logging
>>>
>>>
>>> [1/10] ~  [6/10]: just cleanup for logging branch
>>> [7/10] ~ [10/10]: introduce new traceevents
>>>
>>> Any comments are welcome!
>>
>> In sg3_utils there are now string yielding equivalents
>> to the sense buffer "print" functions. They take a form
>> like this:
>>    char * get_sense_str(const unsigned char * sense_buffer,
>>                         int sb_len, int blen, char * b);
>>
>> So this just does the hard work of decoding the sense buffer
>> (or saying it is invalid) the result of which it places in
>> buffer 'b'. And 'b' is returned (so this function can be in
>> the arguments of a driver's printing function).
>>
>> Adding such string functions would give other parts of the
>> SCSI subsystem the capability of tailoring their own
>> messages that include sense data information.
>>
>>
>> Existing sense buffer "print" function could be kept and
>> implemented using the newer "_str" variants. Would that
>> be worth the trouble?
>>
> Hmm. Probably not.
>
> I would rather go the approach we've been taking with the
> VPD pages, and do _not_ decode any sense code data
> (except from the usual sense key/ASC/ASCQ values, of course).
> Instead we should rather ensure that we can get to the raw
> sense code values from userspace so that we can interpret
> it later with userspace tools.
>
> My plan for updating scsi logging is:
>
> - move all lone 'printk' statements into dev_printk() variants
>    and ensure they are printed in one line to avoid breaking
>    logging statements up under high load
> - Update scsi_trace to use the functionality from constants.c
> - Convert the current scsi_logging mechanism over to tracepoints.
>
> The first bit is mostly done; I'll be sending the patchset for review.
> The hard part is the third bit; would be really grand if we can
> model this with the existing scsi_logging_level interface intact.
> But not sure if that's possible nor if it's desirable.
>
> Btw, _now_ would be a good chance to send an update of constants.c
> with latest SPC bits ...

 From constants.c:
  * Updated to SPC-4 T10/1713-D Rev 36g, D. Gilbert 20130701

Not much has changed between then and now (37a). There is a
lot pending for SPC-5 plus all the ZBC stuff, little of which
has hit the drafts yet. WRITE ATOMIC and a few new asc/ascq
codes is about all that I have noticed. Even when new asc/ascq
strings are approved, it needs the SPC4/5 technical editor to
allocate numbers for them.

So even if the timing is good from the kernel POV, not much
is available. The next T10 meeting is in a few weeks, lets
see what happens there.

Doug Gilbert


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