Re: updating kernel to 2.6.13-rc1 from 2.6.12 + CONFIG_DEVFS_FS + empty /dev

[Willy Tarreau]

Hi Eric,

On Sat, Jul 02, 2005 at 09:22:20AM +0200, Eric Valette wrote:
> Greg KH wrote:
> 
> > Why?  Why not put it in ROM with your kernel image, look at how the
> > kernel build process does it with the "built-in" initramfs.
> 
> Well, nowadays, most system have only flash because ROM does not enable
> to do firmware upgrade. Second, putting it in the kernel or as a
> separate flash section or in an initrd does not change the problem :
> something has to be stored on non volatile memory whereas you do not
> need that for devfs (except devfs code itself of course) but then you
> have udev instead of devfs...

Well, although I've never used udev because I've been using sort of an
equivalent called "preinit" for 4 years now, I don't totally agree with
you about the firmware upgrade : when you package your systems to allow
the customer to perform "firmware" upgrades, your image is already very
specific to a hardware model, and I don't see why you would need to
create /dev entries independantly from the kernel or rootfs. Speaking
for myself, my .preinit script which describes how to fill /dev entries
is on the rootfs and does not need to change once packaged.

However, I agree that I encountered difficulties using this system on
more generic hardware, because sometimes the raid devices did not exist,
or things like this caused trouble.

IMHO, a generic system should use a full /dev directory and an embedded
system should use just the strict minimum necessary for the specific
hardware to run.

> > I boot my boxes with nothing in /dev and have been for almost a year
> > now.  udev works just fine for this, and so do some other programs that
> > work like udev does.
> 
> Nothing in /dev but with initramfs. Same cost...
> 
> BTW : valette@tri-yann->df /dev
> Filesystem           1K-blocks      Used Available Use% Mounted on
> tmpfs                    10240      2876      7364  29% /dev
> 
> 
> 2 MB RAM on my PC???  I must be missing something.

I think something went wrong, perhaps something like

   # some_prog >/dev/null 

while null did not exist. My /dev is a tmpfs too, but mounted with size=0,
so that I can only create inodes into it, but cannot write any data. One
other advantage of using size=0 is that "df" does not show it by default.

Cheers,
Willy

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