Re: [PATCH] Open Firmware device tree virtual filesystem

Benjamin Herrenschmidt
2007-01-02T04:58:40Z

> I think there is high value in an OFW filesystem representation
> that gives you _EXACTLY_ what the OFW command line prompt does
> when you try to traverse the device tree from there, and that
> is what openpromfs tries to do.

Except that every OFW implementation I have here shows you different
things for the same original binary data :-)

> If you want raw access, use a character device or a similar auxilliary
> access to the data items. Another idea is to provide a seperate file
> operation (such as ioctl) on the OFW property files in order to fetch
> things raw and in binary.
>
> When I get some binary data out of a procfs or sysfs file I feel like
> strangling somebody. I'm grovelling around in a filesystem from the
> command line so that I can get some information as a user. If you
> don't give me text I can't tell what the heck it is.
>
> Simple system tools should not need to interpret binary data in
> order to provide access to simple structured data like this, that's
> just stupid.

I would agree with you if the data was properly typed in the first place
but it's not, thus you end up with heuristics and I hate heuristics in
the kernel :-) Now, that's also why everybody on ppc has "lsprop" at
hand which does the "pretty printing" thing.

I like being able to have a simple way (ie. tar /proc/device-tree) to
tell user to send me their DT and have in the end an exact binary
representation so I can actually dig for problems, like a wrong phandle
in an interrupt-map or stuff like that...

Cheers,
Ben.