Re: [PATCH] creating link /dev/root to device / is mounted from

[Matthias Schwarzott <zzam@gentoo.org>]

On Freitag, 20. April 2007, Kay Sievers wrote:
> On 4/20/07, Matthias Schwarzott <zzam@gentoo.org> wrote:
> > Some software (like hal) needs the /dev/root link (as /proc/mounts can
> > contain it).
>
> Right, but HAL doesn't need it, it just assumes that device-file
> entries in /proc/mounts are also available in /dev.
>
> The "/dev/root missing but in /proc/mounts" only happens for people
> who run their own compiled kernels without an initramfs.
>
> > The attached patch contains one program which compares the major/minor
> > number supplied to it on the command-line with the numbers of the device
> > / is located on.
> > It is used with this rule (see 60-root_link.rules):
> > SUBSYSTEM="block", PROGRAM="blockdev_is_root $major $minor",
> > SYMLINK+="root"
>
> Why do we want to run a program for _every_ block device, just to
> create /dev/root? It's an operation you only need to do once at
> bootup, and the root-device is obviously already there, before you
> start udev out of the rootfs. :)
>
I think this is not too bad, as the program itself is only around 3k size.

> The udev init-script checks if /dev is already mounted with tmpfs from
> initramfs, if not, it will need to do it, and at that point, we can
> just mknod /dev/root, can't we?

Well, our initramfs does not move its /dev to new mounted root filesystem, but 
we get a completely fresh tmpfs.

We also can just have a program to write out major/minor of "/" and then mknod 
it (outside of udev)
But I really like a link better.
Here I also can search udev-database (or whatever)

For example when /usr is already mounted (for udevinfo):
dev_nr=$(root_get_dev_nr)
dev_path=$(udevtrigger --verbose --attr-matchfiv=${dev_nr})
dev_name=$(udevinfo -q name --path ${dev_path})
ln -s /dev/${dev_name} /dev/root


Or inject some rule into udev like
ATTR{dev}="${dev_nr}", SYMLINK+="root"
But how to inject? /etc is read-only at udevd starting. Or can rule-files 
include other rule files? Like in /dev/.udev/

Matthias

-- 
Matthias Schwarzott (zzam)

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