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

[Hannes Reinecke]

On 08/22/2014 09:54 PM, Douglas Gilbert wrote:
> On 14-08-12 11:13 PM, Yoshihiro YUNOMAE wrote:
> > Hi Douglas,
> >
> > Thank you for your comment.
> >
> > (2014/08/08 22:07), 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?
> >
> > I have already sent the idea using local buffer on this February,
> > but it was rejected by James (*1). By using stack region for local
> > buffer, stack overflow can occur. So, I implemented this feature
> > to atomically output an error message with device information.
> >
> > (*1) https://lkml.org/lkml/2014/5/20/742
>
> Hi,
> In the "_str" variants that I referred to, the caller provides
> the buffer and its length. The responsibility of the
> implementation of those "_str" variants is to use that
> buffer, not exceed it, and make sure that it is null terminated
> on return.
>
> Can't see any inherent threat to the stack size there, and if
> there is then that is just bad design by the caller.
>
> The advantage of the "_str" variants is that the caller can
> supply context and print/log a more useful message, perhaps
> including the caller's __func__ . That message could include
> sense information (perhaps truncated to 128 bytes, say),
> and be output as a single unit.
>
> IMO too many log messages are multi-line and in a noisy,
> misbehaving system those messages can be interleaved
> with other "noise" making them difficult to decipher.
Precisely, and that is what my patchset is trying to address.

I'm currently porting it to core-for-3.18, will be posting it
for review once it's done.

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
hare@xxxxxxx			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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