linux-kernel - Re: [PATCH 0/5] initmpfs v2: use tmpfs instead of ramfs for rootfs

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Message-ID: <51E88176.6040505@zytor.com>
Date:	Thu, 18 Jul 2013 16:59:50 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Rob Landley <rob@...dley.net>, linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Jeff Layton <jlayton@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Jim Cromie <jim.cromie@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Sam Ravnborg <sam@...nborg.org>,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH 0/5] initmpfs v2: use tmpfs instead of ramfs for rootfs

On 07/17/2013 04:06 PM, Andrew Morton wrote:
> On Tue, 16 Jul 2013 08:31:13 -0700 (PDT) Rob Landley <rob@...dley.net> wrote:
> 
>> Use tmpfs for rootfs when CONFIG_TMPFS=y and there's no root=.
>> Specify rootfstype=ramfs to get the old initramfs behavior.
>>
>> The previous initramfs code provided a fairly crappy root filesystem:
>> didn't let you --bind mount directories out of it, reported zero
>> size/usage so it didn't show up in "df" and couldn't run things like
>> rpm that query available space before proceeding, would fill up all
>> available memory and panic the system if you wrote too much to it...
> 
> The df problem and the mount --bind thing are ramfs issues, are they
> not?  Can we fix them?  If so, that's a less intrusive change, and we
> also get a fixed ramfs.
> 

mount --bind might be useful to fix for ramfs in general (as ramfs
should provide minimal standard filesystem functionality, and that one
counts, I believe), but honestly... we should have had tmpfs as a root
filesystem option either as rootfs or as an automatic overmount a long
time ago.

The automatic overmount option (that is tmpfs on top of rootfs) is nice
in some ways, as it makes garbage-collecting the inittmpfs trivial; this
might save some boot time in the more conventional root scenarios.  On
the other hand, it doesn't exactly seem to be a big problem to just
unlink everything.

	-hpa

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