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SubjectRE: Dynamic Devices
Date
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Hi

> > method of having major,minor device files in /dev is going to have
to
> > go dynamic at some point or other (especially with the advent of
hot
>
> Not true. You can map vast major/minors to files, you know.

But to accomodate vast major/minor combinations you have to increase
the size of dev_t which (by your own words) will breaking everything.
That sounds like too high a cost to me.

> True. Use rm(1). Note "not used" is not the same as "device is not
present
> right now". F.ex, I want /dev/fd0 stay around if only to carry
permissions
> for floppies I insert into the drive.

Obviously, but I have a whole truck load of SCSI and goodness knows
what else entries that I don't use because I don't own anything to
connect to them. i didn't get any choice about those, my distro put
them there. I could remove them, but the effort involved isn't really
worth it. However, I would like it cleaned up (messy file systems piss
me off ;)

> Also note that the "callback to userland" scheme that was in the
> kernel was scrapped some time ago as too fragile and too much
overhead:
> kerneld became kmod.

So scrap devfs and write kdevfs ;)

> I just don't get it. Even if you have to hack MAKEDEV to recognize
modems,
> and set them up with your defaults.

Wouldn't it be nicer to have it done for you?

> The current scheme is totally transparent, without any extra
crutches to
> get it limping along. So it is a loose-loose situation.

It's largely transparent to new users because distros create hundreds
of devices so that John Q Newbie will never have to worry his poor
little head about mknod'ing or using MAKEDEV. That's not really
transparent. It's not much of a big deal either. I don't think the
issue here is really the average user and his need for a few devices
here and there, but maximising the potential of the kernel. In the
same way that a tiny fraction of linux users require 4GB ram support,
but it has been put in, so, only a tiny fraction may need thousands of
devices, but it should still be catered for (especially if it then
makes the usage neater for everyone else).

> I'm not arguing against devfs, I'm arguing against the idea that a
dynamic
> naming scheme for devices will magically manage your devices for
you. It
> just can't.

It's certainly a non-trivial problem, but it's not something that
"can't" be done.

> > I'm totally unbiased because I know nothing about the
implementation
> > of devfs or traditional devices,
>
> Then you can't know how much this costs, kernel-wise.

and yet you advocate changing the dev_t structure which you claim will
break everything (and worse, it is userspace stuff). That sounds like
a particularly horrific cost to me.

> for i in 0 1 2 3 4 5; do
> MAKEDEV usb$i
> done
>
> is so hard that the kernel _must_ do it for you?

That is an oversimplified example that doesn't address the issues
being discussed here.


- ---
_____ _ _ _____
| __ | |___ ___| |_ ___| __|_ _ ___ Chris "Ng" Jones
| __ -| | .'| _| '_|___|__ | | | | chris@black-sun.co.uk
|_____|_|__,|___|_,_| |_____|___|_|_| www.black-sun.co.uk
S o f t w a r e

"Linux is beating Windows" - David Cole, Microsoft Executive

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