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Old 07-16-2012, 01:53 PM
Ian Stakenvicius
 
Default udev <-> mdev

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On 15/07/12 09:00 PM, Maxim Kammerer wrote:
> On Mon, Jul 16, 2012 at 3:30 AM, Duncan <1i5t5.duncan@cox.net>
> wrote:
>> Thinking in that direction does stimulate yet another idea, tho.
>> What about a squashfs root? AFAIK squashfs is read-only at use
>> time, thus enforcing actually mounting something else to write
>> anything, eliminating many of the down sides of sticking with the
>> initial ramfs root, but it would allow the same flexibility in
>> terms of sticking whatever into it at create-time, while only
>> taking the memory necessary for what's actually stuck in it at
>> create-time.
>
> It is possible, see:
> https://github.com/mkdesu/liberte/blob/master/src/root/initrd/init
> https://github.com/mkdesu/liberte/blob/master/src/etc/fstab
>
> The setup above is somewhat different from what you have in mind
> (SquashFS image is located on disk, and contains the complete live
> filesystem, not just a skeleton), so mounting read-writable
> branches can be deferred to the regular post-initramfs services
> (such as localmount) — on the other hand, maybe you want to do the
> same (mount branches read-only in initramfs, and remount them
> read-write in an init.d service).
>

...if going this route, why not simply not bother to pivot_root out of
the initramfs at all? or pivot_root but only into a directory
structure still sitting in the initramfs? As long as all non-root
bits are in separate storage, you can mount 'em all in the appropriate
place...


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Old 07-16-2012, 05:52 PM
Duncan
 
Default udev <-> mdev

Ian Stakenvicius posted on Mon, 16 Jul 2012 09:53:20 -0400 as excerpted:

> ...if going this route, why not simply not bother to pivot_root out of
> the initramfs at all? or pivot_root but only into a directory structure
> still sitting in the initramfs? As long as all non-root bits are in
> separate storage, you can mount 'em all in the appropriate place...

I'm not sure whether that was asked of me or Maxim K, but that was
beginning to be my conclusion as well. See the earlier comment about not
even using an initr* at all, "tho this would be close".

--
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
 
Old 07-29-2012, 11:31 AM
Luca Barbato
 
Default udev <-> mdev

On 07/14/2012 03:21 AM, Olivier Crête wrote:
> Seriously, mdev is a just a bad and now useless hack, it does nothing
> more than using devtmpfs. You do not need udev for a very simple system.
> If you system is a bit more complicated, than udev is what you want. It
> works fine on millions of shipping devices.
>
> And on any new embedded platform, one should seriously think about using
> systemd too. It is very lean, replaces most of the giant, unmaintainable
> shellscripts that you find in many devices with smaller compiled code,
> and was designed to be a good fit for embedded devices.

Last time I looked at systemd it was anything that lean.

Obviously you can say that if you already need dbus and glib and ...
${systemd_deplist} it doesn't count.

Likewise if you are already using busybox it comes with a quite rich shell.

Most depends on what you consider embedded.

lu

--

Luca Barbato
Gentoo/linux
http://dev.gentoo.org/~lu_zero
 
Old 07-29-2012, 11:38 AM
Luca Barbato
 
Default udev <-> mdev

On 07/14/2012 04:34 AM, Canek Peláez Valdés wrote:
> On Fri, Jul 13, 2012 at 9:32 PM, Canek Peláez Valdés <caneko@gmail.com> wrote:
> [snip]
>> A lot of that is optional. The only hard dependencies are:
>>
>>> =sys-apps/kmod-5
>>> =sys-apps/util-linux-2.20
>> dev-util/gperf
>>> =dev-util/intltool-0.40.0
>> virtual/pkgconfig
>> virtual/os-headers
>>
>> Everything else is optional. I repeat: the idea that udev is somewhat
>> "bloated" or "fat" is really incorrect.

> Little correction: inherit autotools brings things like automake and
> libtool, but then again, almost *every* Gentoo installation has those.

build dependencies should not count. =)

The bare udev shouldn't be that huge, then you start look at the glib
integration and such and it might get a bit more than you'd like.

Forking udev and making sure it stays as lean as possible isn't that bad.

Making mdev a bit richer and enjoy the speed advantage of busybox over
stand alone shells could be another option.

Most of the perceived speed in non-shell init systems is due not having
to spawn as many processes. A full busybox wouldn't spawn many processes.

lu

--

Luca Barbato
Gentoo/linux
http://dev.gentoo.org/~lu_zero
 
Old 07-30-2012, 04:44 PM
"Walter Dnes"
 
Default udev <-> mdev

On Sun, Jul 29, 2012 at 01:38:28PM +0200, Luca Barbato wrote

> Forking udev and making sure it stays as lean as possible isn't that bad.

That describes mdev to a T. No need to re-invent the wheel.

> Making mdev a bit richer and enjoy the speed advantage of busybox
> over stand alone shells could be another option.

The busybox people would probably not want "additional functionality"
built-in. A better route would be "mdev helper programs" or "shims"
that we can add to Gentoo as required. Actually, shell scripts
launched by /etc/mdev.conf can be quite powerful. E.g. wiki page
https://wiki.gentoo.org/wiki/Mdev/Automount_USB has ash scripts to
implement auto(un)mounting of USB devices. It works for me, but I'm
waiting for feedback from other users before moving it out of beta
("Work In Progress") status. Once I'm confident in the scripts, I'll
link to them from the main mdev page at
https://wiki.gentoo.org/wiki/Mdev In case you're wondering, I'm not a
C programmer, so scripting was the only available tool for me.

> Most of the perceived speed in non-shell init systems is due not
> having to spawn as many processes. A full busybox wouldn't spawn
> many processes.

It would be an interesting project to make a busybox-based Gentoo
fork. But there are differences between busybox utilities and
standalone gnu utilities. This is especially important for a
source-based distro like Gentoo, where all sorts of gnu utilities
get excercised by build scripts each time you do an update.

--
Walter Dnes <waltdnes@waltdnes.org>
 

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