linux-kernel - Re: [PATCH 05/10] drivers/char: Support compiling out /dev/zero

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Message-ID: <20150128215106.GA6338@cloud>
Date:	Wed, 28 Jan 2015 13:51:06 -0800
From:	josh@...htriplett.org
To:	Pavel Machek <pavel@....cz>
Cc:	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/10] drivers/char: Support compiling out /dev/zero

On Wed, Jan 28, 2015 at 10:07:51PM +0100, Pavel Machek wrote:
> On Fri 2015-01-23 12:37:11, Tom Zanussi wrote:
> > Some embedded systems with tightly controlled userspace have no use
> > for /dev/zero, and could benefit from the size savings gained by
> > omitting it.  Add a new EMBEDDED config option to disable it.
> > 
> > bloat-o-meter (based on tinyconfig):
> > 
> > add/remove: 0/3 grow/shrink: 0/1 up/down: 0/-391 (-391)
> > function                                     old     new   delta
> > chr_dev_init                                 162     147     -15
> > mmap_zero                                     16       -     -16
> > zero_fops                                    116       -    -116
> > zero_bdi                                     244       -    -244
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> 
> I'm not sure that 400 bytes are worth additional Kconfig noise. .. and
> pretty much everyone needs /dev/zero...

Relatively few, actually, given MMAP_ANONYMOUS.  Memory isn't allocated
via an mmap of /dev/zero.  It's useful for systems with shells that want
to redirect from it or read from it, but less useful for environments
with entirely compiled code.

/dev/null is much more commonly needed, though there are still systems
that won't need it (and can just disable read/writes on an fd entirely
rather than duping /dev/null to that fd).

That said, I'd be entirely in favor of consolidating many of these
"miscellaneous character device" options into a couple of Kconfig
options.  It doesn't seem critical to *individually* control each of
these files in /dev.

Personally, I'm hoping that we eventually end up with a disableable
CONFIG_CHAR similar to CONFIG_BLOCK.

- Josh Triplett
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