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-   -   udev <-> mdev (http://www.linux-archive.org/gentoo-development/682905-udev-mdev.html)

Ian Stakenvicius 07-12-2012 01:37 PM

udev <-> mdev
 
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On 11/07/12 11:40 PM, Walter Dnes wrote:
> On Wed, Jul 11, 2012 at 09:49:18AM -0400, Michael Mol wrote
>> Walter Dnes (very active over in gentoo-user) has put a lot of
>> work into testing and documenting mdev as an alternative for
>> udev. There's been a good deal of success there, up to and
>> including it working with GNOME 2. The work's been documented on
>> the wiki: https://wiki.gentoo.org/wiki/Mdev
>
> I'm now testing automount under mdev. No GUI required. I hope to
> have a wiki page up soon.
>
> As for GNOME and KDE, they're trying to become OS's in their own
> right. What can I say? There are a lot of alternative desktop
> environments and window managers. That's my target.
>

Out of curiosity, since mdev is (i assume) more than complete enough
to handle mounting, would it be possible to initially start with mdev
and then hand over control to udev (if there was a need for udev, that
is) , to avoid initramfs with separate /usr ?

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"Walter Dnes" 07-12-2012 08:07 PM

udev <-> mdev
 
On Thu, Jul 12, 2012 at 09:37:33AM -0400, Ian Stakenvicius wrote

First a disclaimer... I am not a C programmer, let alone a developer.
I feel like I've been dragged into this kicking and screaming in order
to save the Gentoo that I remember from a few years ago.

> Out of curiosity, since mdev is (i assume) more than complete enough
> to handle mounting, would it be possible to initially start with mdev
> and then hand over control to udev (if there was a need for udev, that
> is) , to avoid initramfs with separate /usr ?

I think that's exactly how initramfs itself works. You might be able
to use an initrd instead of initramfs. See Zac Medico's posting at...
http://archives.gentoo.org/gentoo-dev/msg_20749880f5bc5feda141488498729fe8.xml
That was the clue that got me started on replacing udev with mdev.

Once you have psuedo-filesystems and partitions mounted, you need to
shut down mdev and start up udev. And make sure that
/proc/sys/kernel/hotplug points to udev.

If you want to get fancy, you can boot from a separate small boot
partition, or for that matter a USB key. Then either chroot or
pivot_root into the udev environment. For pivot_root man pages see
http://linux.die.net/man/8/pivot_root and
http://linux.die.net/man/2/pivot_root

--
Walter Dnes <waltdnes@waltdnes.org>

William Hubbs 07-12-2012 10:29 PM

udev <-> mdev
 
Hi all,

On Thu, Jul 12, 2012 at 04:07:41PM -0400, Walter Dnes wrote:
> On Thu, Jul 12, 2012 at 09:37:33AM -0400, Ian Stakenvicius wrote
>
> First a disclaimer... I am not a C programmer, let alone a developer.
> I feel like I've been dragged into this kicking and screaming in order
> to save the Gentoo that I remember from a few years ago.
>
> > Out of curiosity, since mdev is (i assume) more than complete enough
> > to handle mounting, would it be possible to initially start with mdev
> > and then hand over control to udev (if there was a need for udev, that
> > is) , to avoid initramfs with separate /usr ?
>
> I think that's exactly how initramfs itself works. You might be able
> to use an initrd instead of initramfs. See Zac Medico's posting at...
> http://archives.gentoo.org/gentoo-dev/msg_20749880f5bc5feda141488498729fe8.xml
> That was the clue that got me started on replacing udev with mdev.

initrd is deprecated and has been for a long time; you should use
initramfs.

> Once you have psuedo-filesystems and partitions mounted, you need to
> shut down mdev and start up udev. And make sure that
> /proc/sys/kernel/hotplug points to udev.

If you are using udev, /proc/sys/kernel/hotplug should be empty; do not
point this to udev.

Thanks,

William

Duncan 07-13-2012 05:58 AM

udev <-> mdev
 
William Hubbs posted on Thu, 12 Jul 2012 17:29:31 -0500 as excerpted:

>> And make sure that
>> /proc/sys/kernel/hotplug points to udev.
>
> If you are using udev, /proc/sys/kernel/hotplug should be empty; do not
> point this to udev.

Yes. I've not changed that setting from whatever the default is, and I
guess udev moved its hook out from there quite some time ago so it's
pointing at nothing, but having that actually point to something is known
in kernel circles to lead to a lot of unnecessary grief. They're
seriously thinking about (and may be planning on) removing that option
from the kernel entirely, to keep people configuring their first kernels
from getting themselves in trouble, but of course that's now part of the
kernel/userspace interface, so it isn't allowed to just disappear like
kernel/kernel interfaces can. At minimum they'd likely have to have it
on the deprecation and removal schedule for awhile. (I've not checked to
see if it's there already.)

--
Duncan - List replies preferred. No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman

"Walter Dnes" 07-13-2012 08:04 PM

udev <-> mdev
 
On Fri, Jul 13, 2012 at 05:58:25AM +0000, Duncan wrote

> They're seriously thinking about (and may be planning on) removing
> that option from the kernel entirely, to keep people configuring
> their first kernels from getting themselves in trouble, but of course
> that's now part of the kernel/userspace interface, so it isn't allowed
> to just disappear like kernel/kernel interfaces can. At minimum
> they'd likely have to have it on the deprecation and removal schedule
> for awhile. (I've not checked to see if it's there already.)

So what happens to people using mdev? Do we have to switch from
Linu-x to Lenna-x?

--
Walter Dnes <waltdnes@waltdnes.org>

Richard Yao 07-13-2012 08:12 PM

udev <-> mdev
 
On 07/13/2012 04:04 PM, Walter Dnes wrote:
> On Fri, Jul 13, 2012 at 05:58:25AM +0000, Duncan wrote
>
>> They're seriously thinking about (and may be planning on) removing
>> that option from the kernel entirely, to keep people configuring
>> their first kernels from getting themselves in trouble, but of course
>> that's now part of the kernel/userspace interface, so it isn't allowed
>> to just disappear like kernel/kernel interfaces can. At minimum
>> they'd likely have to have it on the deprecation and removal schedule
>> for awhile. (I've not checked to see if it's there already.)
>
> So what happens to people using mdev? Do we have to switch from
> Linu-x to Lenna-x?
>

mdev would need to switch to the netlink hotplug interface.

Maxim Kammerer 07-13-2012 10:49 PM

udev <-> mdev
 
On Fri, Jul 13, 2012 at 11:12 PM, Richard Yao <ryao@gentoo.org> wrote:
> mdev would need to switch to the netlink hotplug interface.

I think that's quite unlikely, since mdev is not a daemon. Perhaps by
the time /proc/sys/kernel/hotplug is gone, mdev advocates will have
settled on some early udev fork. [1]

[1] http://archives.gentoo.org/gentoo-dev/msg_72b87bf5888d6f6e675429dbfe420db5.xml

--
Maxim Kammerer
Liberté Linux: http://dee.su/liberte

"Walter Dnes" 07-14-2012 12:13 AM

udev <-> mdev
 
On Sat, Jul 14, 2012 at 01:49:32AM +0300, Maxim Kammerer wrote
> On Fri, Jul 13, 2012 at 11:12 PM, Richard Yao <ryao@gentoo.org> wrote:
> > mdev would need to switch to the netlink hotplug interface.
>
> I think that's quite unlikely, since mdev is not a daemon. Perhaps by
> the time /proc/sys/kernel/hotplug is gone, mdev advocates will have
> settled on some early udev fork. [1]

Do you realize this would effectively kill linux in the embedded
device area? Udev, even without the systemd code, is simply to large
for embedded devices.

--
Walter Dnes <waltdnes@waltdnes.org>

Canek Peláez Valdés 07-14-2012 12:36 AM

udev <-> mdev
 
On Fri, Jul 13, 2012 at 7:13 PM, Walter Dnes <waltdnes@waltdnes.org> wrote:
> On Sat, Jul 14, 2012 at 01:49:32AM +0300, Maxim Kammerer wrote
>> On Fri, Jul 13, 2012 at 11:12 PM, Richard Yao <ryao@gentoo.org> wrote:
>> > mdev would need to switch to the netlink hotplug interface.
>>
>> I think that's quite unlikely, since mdev is not a daemon. Perhaps by
>> the time /proc/sys/kernel/hotplug is gone, mdev advocates will have
>> settled on some early udev fork. [1]
>
> Do you realize this would effectively kill linux in the embedded
> device area? Udev, even without the systemd code, is simply to large
> for embedded devices.

The guys from ProFUSION would disagree with you:

http://profusion.mobi/

It is a "a software development company focused on embedded systems",
and several of its employees contribute code and ideas for systemd, so
they also use udev. For embedded systems.

The idea that udev "is simply to large" is simply incorrect, I believe.

Regards.
--
Canek Peláez Valdés
Posgrado en Ciencia e Ingeniería de la Computación
Universidad Nacional Autónoma de México

Michael Mol 07-14-2012 12:40 AM

udev <-> mdev
 
On Fri, Jul 13, 2012 at 8:13 PM, Walter Dnes <waltdnes@waltdnes.org> wrote:
> On Sat, Jul 14, 2012 at 01:49:32AM +0300, Maxim Kammerer wrote
>> On Fri, Jul 13, 2012 at 11:12 PM, Richard Yao <ryao@gentoo.org> wrote:
>> > mdev would need to switch to the netlink hotplug interface.
>>
>> I think that's quite unlikely, since mdev is not a daemon. Perhaps by
>> the time /proc/sys/kernel/hotplug is gone, mdev advocates will have
>> settled on some early udev fork. [1]
>
> Do you realize this would effectively kill linux in the embedded
> device area? Udev, even without the systemd code, is simply to large
> for embedded devices.

I'll venture a guess the solution will be to create a shim daemon
which turns around and launches udev.

--
:wq


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