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SubjectRe: DEVFSv50 and /dev/fb? (or /dev/fb/? ???)
On Wed, 5 Aug 1998, Andrea Arcangeli wrote:
> On Tue, 4 Aug 1998, Shawn Leas wrote:
>
> >Specifically, what is ugly about it? Is it intrinsic in nature, or
> >something fixable? Is the design flawed? Then how? Back up your
>
> I don' t know about the Theodore idea of ugly but I agree with him. _I_
> see devfs flowed by its start. I just explained my thoughts about devfs
> some month ago before the first release of devfs. devfs is a workaround.
> We would not need devfs at all if the kdev_t would be a 64 bit unsigned
> integer.
>
> Instead of reply me that with devfs the root device _can_ be mounted
> readonly and we _can_ boot with a root fs with no major/minor number
> support, please tell me that you need to use these features. We could also
> write a videogame in the kernel and eventually play with it before mount
> the root device if you really want not used features (even if this example
> is not the right one, the exciting videogame probably would be played a
> lot ;-).

Simply having inodes with device info (Major/minor devices) incurrs a
penalty in that you have these inodes on a filesystem on disk (or maybe
RAM), in any case you are busying up yet another subsystem, and so
on. devfs is a shorter route to access devices, and this improves (on
some large scale systems) performance when you have a zillion
pseudodevices and you are accessing them a lot. Even if you give me
"Dcache speeds that up", I can say, well, that's only true while the
entries are in the dcache.

Think of having proc be a collection of physical directories with
physical files on disk. I know, this is not an exactly similar idea, but
the devfs shares some procfs-like goodies...

This is, of course, not to mention that device files only exist if they
are really there... Imagine, just

if [ -r /devfs/ide/hd/blah ]; then
echo "you have an ide disk"
fi

if [ -d /dev/fs/ide/cd ]; then
echo "you have a cdrom [or support for one]"
fi

or something like that... It's VERY NICE from a system management POV. I
can't wait to see what distributions do with it.

> I had to say that I never tried devfs and that it could be a very
> confortable workaround but I can' t like it ;-). Probably I' ll try soon
> though. I' m afraid to say this again and after the sure good work of
> Richard...

Well, I cannot gaurantee the total correctness of exactly everything I
claim, but I do understand that the devfs is a shortcut from userspace to
devices. This is a "Good Thing" (tm), in my book.

-Shawn
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