From mboxrd@z Thu Jan  1 00:00:00 1970
From: Loic Dachary <loic@dachary.org>
Subject: Resolving the ruleno / ruleset confusion
Date: Fri, 08 Aug 2014 15:38:13 +0200
Message-ID: <53E4D2C5.8050600@dachary.org>
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To: Ma Jianpeng <majianpeng@gmail.com>, "Chen, Xiaoxi" <xiaoxi.chen@intel.com>
Cc: Ceph Development <ceph-devel@vger.kernel.org>

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Hi,

As you noticed, there are places where ruleset and ruleno / ruleid are us=
ed interchangeably although they are not. This is a source of subtle bugs=
 that can be hard to trace. By default ruleid and ruleset are the same, b=
ut dumping a crush map including

rule data {
        ruleset 0
        type replicated
        min_size 1
        max_size 10
        step take default
        step chooseleaf firstn 0 type host
        step emit
}
rule metadata {
        ruleset 1
        type replicated
        min_size 1
        max_size 10
        step take default
        step chooseleaf firstn 0 type host
        step emit
}

and swapping the rules as follows

rule metadata {
        ruleset 1
        type replicated
        min_size 1
        max_size 10
        step take default
        step chooseleaf firstn 0 type host
        step emit
}

rule data {
        ruleset 0
        type replicated
        min_size 1
        max_size 10
        step take default
        step chooseleaf firstn 0 type host
        step emit
}

will have ruleset 1 with rule id 0 and ruleset 0 with rule id 1

Since the ruleset is the only reliable number, from the user point of vie=
w, we could simply change CrushWrapper.h to never return the rule id and =
assume only ruleset are given in argument, even where it currently claims=
 to be a rule id.

The downside is that looking up the ruleset implies iterating over all th=
e rules, but that's probably not an issue.

What do you think ?

Cheers
--=20
Lo=EFc Dachary, Artisan Logiciel Libre


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