Re: [gentoo-dev] Suggestion for getting rid of udev

[Nathan Phillip Brink <binki@gentoo.org>]

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On Wed, Oct 12, 2011 at 12:40:23AM -0400, Walter Dnes wrote:
> Hi all
> 
>   Recently, there was a firestorm on the gentoo-user list over the idea
> that udev would eventually require /usr to be on the same physical
> parition as /, or else use initramfs, which is its own can of worms. I'm
> not a programmer, let alone a developer.  Rather than merely ranting, I
> went and searched for an alternative.
...
> 
>   Another option is to take the current Gentoo setup, drop udev and
> use mdev in the same manner as Alpine uses it.  In case anyone asks,
> auto mounting should still be possible.  Attached is an excerpt from
> /var/log/messages from a basic Alpine install.  The kernel messages were
> generated when I inserted a USB key into a usb jack.

Seeing from the prior conversations here (sorry for lack of citation)
and
http://lists.busybox.net/pipermail/busybox/2011-September/076710.html
, I suspect that the root problem isn't with udev itself but with the
udev rules.

The magic which makes automatic userspace configuration possible is in
the udev rules and makes udev appear to be the problem. For example,
if you switch to mdev currently, you will notice that X11's device
autodetection doesn't work so well. (At least for me, X11's
autodetection magically works for detecting input devices with udev
but not with mdev). It is concievable that you could develop a
parallel database of mdev-compatible rules and even let packages
install rules specific to themselves (with modification to mdev
http://lists.busybox.net/pipermail/busybox/2011-September/076666.html
). With these sorts of things, you might figure out a way to make
X11's device autoconfiguration work or perform other device
initialization tasks. But at the same time, you have a good chance of
accidentally introducing a reliance on libraries/programs installed to
/usr. This latter problem is the issue, deciding how much software
should have --prefix=/ versus the normal --prefix=/usr.

You can already try out what using mdev instead of udev is like in
Gentoo. Just add `sys-apps/busybox mdev' to /etc/portage/package.use,
remerge busybox. You must be sure to be using busybox-1.92.2 or later
for bug #83301.

# rc-update add mdev sysinit
# rc-update del udev sysinit

But be 'ware that this isn't guaranteed to provide a successful boot
;-).

> Oct  9 13:46:00 e521 kern.info kernel: [10714.105621] usb 2-8: new high speed USB device using ehci_hcd and address 4
> Oct  9 13:46:00 e521 kern.info kernel: [10714.241353] usb 2-8: New USB device found, idVendor=13fe, idProduct=1e00
> Oct  9 13:46:00 e521 kern.info kernel: [10714.241357] usb 2-8: New USB device strings: Mfr=1, Product=2, SerialNumber=3
> Oct  9 13:46:00 e521 kern.info kernel: [10714.241360] usb 2-8: Product: Patriot Memory  
> Oct  9 13:46:00 e521 kern.info kernel: [10714.241362] usb 2-8: Manufacturer:         
> Oct  9 13:46:00 e521 kern.info kernel: [10714.241364] usb 2-8: SerialNumber: 078215A302CF
> Oct  9 13:46:00 e521 kern.info kernel: [10714.244241] scsi4 : usb-storage 2-8:1.0
> Oct  9 13:46:01 e521 kern.notice kernel: [10715.279753] scsi 4:0:0:0: Direct-Access              Patriot Memory   PMAP PQ: 0 ANSI: 0 CCS
> Oct  9 13:46:02 e521 kern.notice kernel: [10715.930991] sd 4:0:0:0: [sdb] 31326208 512-byte logical blocks: (16.0 GB/14.9 GiB)
> Oct  9 13:46:02 e521 kern.notice kernel: [10715.931980] sd 4:0:0:0: [sdb] Write Protect is off
> Oct  9 13:46:02 e521 kern.debug kernel: [10715.931983] sd 4:0:0:0: [sdb] Mode Sense: 23 00 00 00
> Oct  9 13:46:02 e521 kern.err kernel: [10715.931986] sd 4:0:0:0: [sdb] Assuming drive cache: write through
> Oct  9 13:46:02 e521 kern.err kernel: [10715.935986] sd 4:0:0:0: [sdb] Assuming drive cache: write through
> Oct  9 13:46:02 e521 kern.info kernel: [10715.981381]  sdb: sdb1
> Oct  9 13:46:02 e521 kern.err kernel: [10715.986028] sd 4:0:0:0: [sdb] Assuming drive cache: write through
> Oct  9 13:46:02 e521 kern.notice kernel: [10715.986035] sd 4:0:0:0: [sdb] Attached SCSI removable disk

Unless if I'm missing something, those messages _always_ show up even
if udev or mdev haven't been invoked.

-- 
binki

Look out for missing or extraneous apostrophes!

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