[dm-devel] [PATCH 21/24] dm cache: add trc policy shim

[Alasdair G Kergon]

On Thu, Oct 24, 2013 at 02:30:34PM -0400, Mike Snitzer wrote:
> From: Morgan Mears <morgan.mears at netapp.com>
 
> This commit includes a non-terminal policy (aka "shim") called trc that
> may be stacked ontop of a terminal policy (e.g. mq).
> The second shim, trc, adds function-call-level tracing to the policy
> stack.  By default, an INFO-level log message including function name
> and parameter(s) will be generated whenever most of the cache policy
> interface functions are called.  An interface to increase or decrease
> the verbosity of the trace output is also provided.
 
Firstly, why not call it 'trace' in full, rather than abbreviating it to 3
consonants?

> +++ b/drivers/md/dm-cache-policy-trc.c

> +#define DM_TRC_OUT(lev, p, f, arg...) \
> +	do { \
> +		if (to_trc_policy(p)->trace_level >= lev) \
> +			DMINFO("%s: " f, __func__, ## arg); \
> +	} while (0)

OK for private debugging, but I can't pretend to be very keen on this
one going upstream in this form.   Might this not need to support high
volumes of messages sometimes?  Were other upstream mechanisms
considered?  (E.g. see Documentation/trace).

Alasdair