Re: [RFC PATCH -logging 00/10] scsi/constants: Output continuous error messages on trace

[Douglas Gilbert]

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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