linux-kernel - About 'hash' event trigger patchset

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Message-ID: <CAM9d7ch-ZBYRHmhbHJEXQtS-V_kBPK5nMhtM3bPbHmnY+m-EeQ@mail.gmail.com>
Date:	Wed, 2 Apr 2014 08:31:04 +0000
From:	Namhyung Kim <namhyung@...nel.org>
To:	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: About 'hash' event trigger patchset

Hi Tom,

(Sorry for replying in another thread, I have a problem on mail settings)

I've just read your hash event trigger series, and want to give some feedback.

At first, the change log of 5/5 is actually a better documentation
than in patch 4/5 so I think it should be added to the doc also.  But
the syntax of the hash trigger should be look like:

- # echo hash:key(s):value(s)[:sort_keys()][ if filter] > event/trigger
+ # echo hash:key(s):value(s)[:"sort="sort_key(s)][ if filter] > event/trigger

Also on first example in the changelog of 5/5, key should be
'stacktrace' instead of 'call_site'.

As far as I see in the code, the sort key can receive an optional
descending/ascending modifier, but it's not documented.

One thing I noticed in the main logic is that it seems there's no
limit checking when adding/creating new entry.  In
hash_trigger_entry_create(), there's a check against max_entries but
if it goes beyond the max, it'd just access a NULL pointer AFAICS.  Am
I missing something?  Also I don't know what the difference between
->n_entries and ->total_entries (in hash_data).

I guess you wanted to set ->drops in that case, but I cannot find
where it gets set.  And I'm not sure it's good to check ->drop first,
since entry can find an existing entry and merged to it even if it
reached the max already.

Thanks,
Namhyung
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