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

[Yoshihiro YUNOMAE]

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

Thanks,
Yoshihiro YUNOMAE

--
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@xxxxxxxxxxx


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