mdev race conditions

[Mike Frysinger]

On Tuesday 03 June 2008, Bernard Blackham wrote:
> Mike Frysinger wrote:
> > you'll also need to make sure you do this somewhere which has temporary
> > storage ... otherwise you'll wreck embedded flash systems
>
> /dev is on tmpfs anyway.

not always ... but for the cases which i'm flagging, they'd better be or 
you're already wrecking things :)

> > *shrug* anything not daemon/netlink based looks like a hack to me
>
> And I'm inclined to agree.
>
>  > which means i still dont understand why people dont go use udevd if
>  > they need a real setup.
>
> s/real/reliable/
>
> What good is using mdev if it cannot be relied upon? (apart from using
> mdev -s at boot and an otherwise completely-static /dev).

this is actually a significant base for which mdev is perfect

> [... snip ...]
>
>  > better, just use udevd (which i honestly dont think is a big deal, it
>  > isnt exactly bloated ... it's 76k on x86_64 and it's built for speed,
>  > not size).
>
> It's 66K stripped on arm and built for size (the Makefile for udev-120
> does this by default). 66K is a lot for a critical daemon.

i'd disagree.  ignoring busybox, 66k is pretty damn tight considering 
everything udev offers.

> It does a 
> *lot* of stuff that nobody needs - it maintains a database in /dev/.udev
> of all devices and exports lots of information to userspace which
> probably does not matter to most embedded systems.

it does a *lot* of stuff that people keep asking to add to mdev.  historically 
i declined anything but the bare min stuff as imo, we're wasting time 
reinventing a perfectly good wheel.  Denys seems to be more open to merging 
features.

> I'd like someone to answer my original proposal of whether or not a
> simple daemon running in a loop would suffice. I imagine the resulting
> binary would be a mere few kilobytes in size, as *all* it needs to do is
> serialize requests and pass them to mdev. Nothing more.

writing a standalone binary does not fit the busybox design.  i doubt mdevd 
would be terribly difficult to do with real netlink sockets/daemon.
-mike
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