Matching something against an environment-variable

Matching something against an environment-variable

[Matthias Schwarzott]

Hi!

I just have noticed that comparisons like this are not possible with udev:

something=ENV{MY_VAR}
or
something="$env{MY_VAR}"

The reason I want to use that is: creating /dev/root without executing a 
program for every blockdev.

With some rule like this:
SUBSYSTEM="block", ATTR{dev}=ENV{ROOT_DEV_NR}, SYMLINK+="root"


with variable ROOT_DEV_NR be either set by 
A. SUBSYSTEM="block", IMPORT{file}+="/dev/.udev/root_dev_nr"
and that file is created by udev-startscript

B. injecting the env-var with
udevcontrol env ROOT_DEV_NR=$(get_root_dev)
after udevd has been started

I think the variant  something=ENV{MY_VAR} should not be too complicated to 
realize.

Matthias

-- 
Matthias Schwarzott (zzam)

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Re: Matching something against an environment-variable

[Kay Sievers]

On 4/27/07, Matthias Schwarzott <zzam@gentoo.org> wrote:
> I just have noticed that comparisons like this are not possible with udev:
>
> something=ENV{MY_VAR}

Key names can't appear on the right side, it's always a quoted value.

> or
> something="$env{MY_VAR}"

Right, this version could be made working, but today we don't apply
format chars before we compare the values.

> The reason I want to use that is: creating /dev/root without executing a
> program for every blockdev.
>
> With some rule like this:
> SUBSYSTEM="block", ATTR{dev}=ENV{ROOT_DEV_NR}, SYMLINK+="root"
>
> with variable ROOT_DEV_NR be either set by
> A. SUBSYSTEM="block", IMPORT{file}+="/dev/.udev/root_dev_nr"
> and that file is created by udev-startscript
>
> B. injecting the env-var with
> udevcontrol env ROOT_DEV_NR=$(get_root_dev)
> after udevd has been started
>
> I think the variant  something=ENV{MY_VAR} should not be too complicated to
> realize.

Why don't you write out a 50-rootdev.rules file before starting udevd?
So you don't need to import anything, or match on globel variables:
   SUBSYSTEM="block", ENV{MAJOR}="8", ENV{MINOR}="5", SYMLINK+="root"

Kay

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Re: Matching something against an environment-variable

[Andrey Borzenkov]

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On Monday 30 April 2007, Kay Sievers wrote:
>
> Why don't you write out a 50-rootdev.rules file before starting udevd?
> So you don't need to import anything, or match on globel variables:
>    SUBSYSTEM=="block", ENV{MAJOR}=="8", ENV{MINOR}=="5", SYMLINK+="root"
>

At least here udev is started when root is still mounted read-only. Of course 
what is possible, in udev.conf

udev_rules="/dev/.udev/rules.d /etc/udev/rules.d"

and drop rootdev.rules under /dev/.udev/rules.d.

-andrey

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Re: Matching something against an environment-variable

[Matthias Schwarzott]

On Montag, 30. April 2007, Kay Sievers wrote:
>
> Why don't you write out a 50-rootdev.rules file before starting udevd?
> So you don't need to import anything, or match on globel variables:
>    SUBSYSTEM="block", ENV{MAJOR}="8", ENV{MINOR}="5", SYMLINK+="root"
>
The problem here is: udev is started before root filesystem is remounted R/W.

At least two solutions to that:
A. Add a symlink in /etc/udev/rules.d/ pointing to somewhere in /dev/.udev/ or 
on any other tmpfs location. And create the file there.

B. Adding some file-inclusion command to udev rule language.

Matthias

-- 
Matthias Schwarzott (zzam)

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