Re: [ANNOUNCE] udev 021 release

["Alexander E. Patrakov" <patrakov@ums.usu.ru>]

On Wednesday 03 March 2004 17:22, Ed Tomlinson wrote:
> On March 03, 2004 04:56 am, Michael Weiser wrote:
> > Normally with static /dev one has a /dev/dsp device for example. As soon
> > as an application tries to open it the kernel would try to load a module
> > "sound" or "char-major-something" if sound support isn't compiled into
> > it. Now with udev I'll never get /dev/dsp in the first place and there's
> > no mechanism like devfs's file open monitoring and subsequent device
> > file creation. So my idea is to initialise /dev with some static files,
> > for hardware I know is there but hasn't had a driver loaded yet. My
> > question is: Is there a nicer and more elegant way than just unpacking a
> > tarball into /dev before starting udevd? A tarball would also break a
> > (theoretical) use of dynamic major/minor numbers by the kernel.
>
> Would it be possible to have something in the module itself?  i.e. We
> create a new macro to add info that a script can use.  This info could live
> in a new file in lib/modules or in the actual module.  This could be used
> to create the static setup dynamicly.

Actually, I am now busy implementing this (if you want, race with me - I am a 
very slow coder). My implementation, however, uses a 
directory: /lib/modules/2.6.3/sys. The entries are supposed to be in sysfs 
format, and defined in modules themseves, like:

MODULE_INFO(syshint, "block/loop0/dev=7:0");

Of course, a change to the depmod program is needed to create this hierarchy 
based on such "syshint" information.

Already found a bad thing with my approach: the loop module accepts a 
parameter max_loop:Maximum number of loop devices (1-256), and we should 
create the same (dynamic!) number of sysfs entries. The mismatch can lead to 
races e.g.:

1) Suppose that we create only one such syshint
2) The initscript creates only one /dev/loop0 device
3) An app wants to open /dev/loop0
4) The kernel modprobes block-major-7-0, i.e. loop
5) Udev is run in order to create all other loop devices, but it runs slowly.
6) An app wants to open /dev/loop1, but udev hasn't created this yet
7) Slow udev finally creates /dev/loop1

-- 
Alexander E. Patrakov



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