linux-kernel - Re: [PATCH] use tmpfs for rootfs v3

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Message-ID: <alpine.LSU.0.999.0810202006050.5225@be1.lrz>
Date:	Mon, 20 Oct 2008 20:13:09 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	Mike Frysinger <vapier.adi@...il.com>
cc:	Bodo Eggert <7eggert@....de>, jeffschroeder@...puter.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] use tmpfs for rootfs v3

On Sun, 19 Oct 2008, Mike Frysinger wrote:
> On Fri, Oct 17, 2008 at 07:16, Bodo Eggert wrote:

> > This patch allows chosing tmpfs instead of ramfs for the root filesystem.
> > Having tmpfs is usefull for running systems from RAM, because it does not
> > risk deadlocking the system and possibly allows swapping. Using tmpfs
> > increases the kernel by 10 bytes on x86_64.
> 
> great option, thanks
> 
> > --- linux-2.6.27.2-numlock/fs/Kconfig   2008-10-10 13:18:34.000000000 +0200
> > +++ linux-2.6.27.3-tmpfs/fs/Kconfig     2008-10-11 15:42:21.000000000 +0200
> > @@ -953,6 +953,27 @@ config TMPFS_POSIX_ACL
> >
> >          If you don't know what Access Control Lists are, say N.
> >
> > +config TMPFS_ROOT
> > +       bool "Use tmpfs instrad of ramfs for initramfs"
> > +       depends on TMPFS && SHMEM
> > +       default n
> > +       help
> > +         This replaces the ramfs used for unpacking the cpio images
> > +         with tmpfs.
> > +
> > +         If unsure, say N
> 
> this should be init/Kconfig and depend on BLK_DEV_INITRD i think.  and
> then update the comment to talk about the initial filesystem rather
> than cpio images.

Maybe, but then you'd have to go to filesystems->pseudo-fs to enable tmpfs,
then to i-don't-remember to set it as the rootfs, and then back to
fs->pseudo-fs to unselect ramfs.

Thinking of it as a tmpfs option makes it much easier to use.

> > +config RAMFS
> > +       bool "Ramfs file system support" if TMPFS_ROOT
> 
> if you have initramfs support disabled, then you should be able to
> disable RAMFS as well.  so perhaps the depend should read like:
> if BLK_DEV_INITRD && TMPFS_ROOT || !BLK_DEV_INITRD

No, since a kernel not having initcpio support will mount rootfs anyway,
create some directories and special files and use them to open the console
and to mount the real root into.
-- 
The enemy diversion you have been ignoring will be the main attack.
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