Re: Documentation for sysfs, hotplug, and firmware loading.

Rob Landley
2007-07-23T23:27:18Z

On Friday 20 July 2007 8:43:49 pm Greg KH wrote:
> On Fri, Jul 20, 2007 at 08:21:39PM -0400, Rob Landley wrote:
> > Ok, back up. /sys/devices does not contain all the information necessary
> > to populate /dev, because it hasn't got things like
> > ramdisks, /dev/zero, /dev/console which are THERE in sysfs, which may or
> > may not be supported by the kernel (the kernel might have ramdisk
> > support, might not).
>
> Welcome to 2007:
>
> $ ls /sys/devices/virtual/mem/
> full kmem kmsg mem null port random urandom zero
> $ ls /sys/devices/virtual/tty/
> console tty12 tty19 tty25 tty31 tty38 tty44 tty50 tty57 tty63
> ptmx tty13 tty2 tty26 tty32 tty39 tty45 tty51 tty58 tty7
> tty tty14 tty20 tty27 tty33 tty4 tty46 tty52 tty59 tty8
> tty0 tty15 tty21 tty28 tty34 tty40 tty47 tty53 tty6 tty9
> tty1 tty16 tty22 tty29 tty35 tty41 tty48 tty54 tty60
> tty10 tty17 tty23 tty3 tty36 tty42 tty49 tty55 tty61
> tty11 tty18 tty24 tty30 tty37 tty43 tty5 tty56 tty62
>
> I suggest you take a close look at the kernel before making statements
> like the above :)

I did:

landley@dell:/sys/devices$ ls /sys/devices/virtual
ls: /sys/devices/virtual: No such file or directory
landley@dell:/sys/devices$ cat /proc/version
Linux version 2.6.20-16-generic (root@terranova) (gcc version 4.1.2 (Ubuntu
4.1.2-0ubuntu4)) #2 SMP Thu Jun 7 20:19:32 UTC 2007

I.E. Ubuntu 7.04, stock. The most recent release, using a 2.6.20 kernel.

I see that what you're talking about is in 2.6.22. Back when I started
writing my document in May, I forgot to check 2.6.22.

> > These things could also, in future, have their major and minor numbers
> > dynamically (even randomly) assigned. That's been discussed on this
> > list.
>
> I tried that once, it will require some core api kernel changes and a
> lot of infrastrucure work to get that to work properly. Not that it
> will never happen in the future, but it's just not a trivial change at
> the moment...

Understood.

> thanks,
>
> greg k-h

Rob
--
"One of my most productive days was throwing away 1000 lines of code."
- Ken Thompson.