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Re: [Sheflug] Where is /dev/eth0 ? What are major & minor device numbers?



On 31 May 2002 07:17:51 +0100
Alex Hudson <home [at] alexhudson.com> wrote:

> On Thu, 2002-05-30 at 23:49, Andrew Basterfield wrote:
> > They're there for compatibility but they're no longer used by the
> > kernel to identify which device a /dev entry corresponds to.
> 
> Your statment was that it doesn't use them, which it clearly does. Try
> reading fs/devfs/base.c; they crop up quite often.

The kernel devfs code presents the device's major/minor if the driver also
has a old style major/minor interface. It does not, however, 'use' them
for device access. It would work without them. That's the point.

> Yes, I agree they are there for compatability, no, you cannot do without
> them.

They are used by lilo and similar userland programs that need to map from
a /dev entry to a physical device outside of the kernel. That's all
they're there for AFAIK. You could take major/minor support out of devfs
and still be able to access the device normally in practically all
applications.

> > > Devfs is filesystem based. "Device Filesystem" = Devfs.
> > 
> > Devfs is not a filesystem, a filesystem is a system for storing files.
> 
> What do you think entries in /devfs are? They're files. Devfs is a
> filesystem. It's code is in linux/fs. Mount shows it as type 'devfs'. 
>
> Trying to argue procfs is less a filesystem than ext2 is fairly
> non-sensical.

Procsfs, devfs, usbfs, devpts et al don't exist on media, therefore they
are virtual. They also offer only limited support for normal filesystem
operations making them IMHO 'less of a filesystem'.

>  Everything is a virtual filesystem, it's even called the VFS.

VFS is not a filesystem and it doesn't pretend to be, it's an abstraction
layer which replaced the original Minix-only fs code in early Linux
kernels, making all filesystems and pseudo-filesystems look a bit like
Minix to the lower levels of the kernel. Just because a filesystem sits
behind VFS doesn't make it virtual. The filesystems are real,
pseudo-filesystems and VFS are virtual.

--Andrew

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