linux-kernel - Re: [PATCH 3/3] dm ioctl: Delete an unnecessary check before the function call "dm_table

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Message-ID: <CAMM=eLfpAiTeqvX17C3agsLXP03UD_Q7DnmhGnO5GjEC0pZa8Q@mail.gmail.com>
Date:	Sun, 8 Feb 2015 09:02:53 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	Alasdair Kergon <agk@...hat.com>, Neil Brown <neilb@...e.de>,
	device-mapper development <dm-devel@...hat.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	Julia Lawall <julia.lawall@...6.fr>,
	kernel-janitors@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] dm ioctl: Delete an unnecessary check before the
 function call "dm_table_destroy"

On Sun, Feb 8, 2015 at 4:55 AM, SF Markus Elfring
<elfring@...rs.sourceforge.net> wrote:
>> Your proposed patch (while technically correct) hurts code clarity.
>
> How many source code readability and understanding challenges does each
> additional condition check cause?

Please don't make a mountain out of a mole hill in an attempt to
defend your robotic patch (I'm quite tired of some of these static
analyzer patch submissions).

FYI, I did stage your other patch for 3.20, see:
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-3.20&id=d0ce7e911c97c7c6df1081dcedfefced82a0c6bf

> Can the affected place become also a bit more efficient?

Efficiency isn't a concern in this instance (it isn't a hot IO path).
And even if it were, a branch (with current code) is more efficient vs
a a jump + branch (your proposed patch) -- in the case that no active
table exists.  Now if it likely that old_map does exist then yes your
patch is always a very slight win.

But given the duality of the calling function (deals with loading a
new map and destroying the old map if it exists) I prefer to keep the
code as is.  Sorry.
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