Re: [gentoo-user] udev + /usr

[Michael Schreckenbauer]

Hi Alan,

On Monday, 12. September 2011 15:02:48 Alan Mackenzie wrote:
> Hi, everybody.
>
> Hope nobody minds me starting a new thread with an accurate name.
>
> Which version of udev is it that has this nauseating feature of needing
> /usr loaded to boot?

> Somewhere in that version's source will be several (or lots of) "/usr".
> Just how difficult is it going to be to replace "/usr/bin" with "/bin"
> throughout the source?

you misunderstood something. udev is able to run arbitrary scripts. Some of 
those scripts are located in /usr/* or need something there. I doubt you will 
find references to /usr in the udev-sources.

> udev is part of the kernel.

No. udev is usperspace.

> How come the kernel hackers aren't up in
> arms about this as much as we are?  Or are they, maybe?  In which case,
> maybe the kernel people would welcome an option to disrequire the early
> mounting of /usr as much as we would.
>
> Anyhow, I'd like to take a peek at the source code which does this evil
> thing.  Would somebody please tell me which version of udev is involved.

Every udev version works this way.
Fixing udev to continue working with separate /usr is far from trivial imo. 
Changing some paths is not the way to go for sure.
First of all, udev has to distinguish between "device not present" and "script 
error of some kind". Failing scripts have to be queued somehow for later 
execution. If a script keeps failing, it has to be removed from that queue, 
with a message to syslog or something like that. If udev needs a script in 
/usr/* to mount /usr then there's a chicken-egg-problem, which could be hard 
to solve (if possible at all without moving things from /usr/ to /).
Note, that I am wild guessing here, I did not study the udev sources or any 
related script/rule :)

> Thanks.

Best,
Michael