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

[Andrey Borzenkov <arvidjaar@mail.ru>]

[-- Attachment #1.1: Type: text/plain, Size: 2449 bytes --]

On Saturday 21 April 2007, Matthias Schwarzott wrote:
> 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.
>

I believe, most iplementations do. Actually how you solve the issue 
with /dev/null & Co. without it?

> 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)
>

Yes that is nice. What about a simple program that can manupulate udev 
database? I am not sure if the format allows it though.

-andrey

> For example when /usr is already mounted (for udevinfo):
> dev_nr=$(root_get_dev_nr)
> dev_path=$(udevtrigger --verbose --attr-match=dev=${dev_nr})
> dev_name=$(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



[-- Attachment #1.2: Type: application/pgp-signature, Size: 189 bytes --]

[-- Attachment #2: Type: text/plain, Size: 286 bytes --]

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/

[-- Attachment #3: Type: text/plain, Size: 226 bytes --]

_______________________________________________
Linux-hotplug-devel mailing list  http://linux-hotplug.sourceforge.net
Linux-hotplug-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel