[TUHS] Device special files

[ron minnich]

Well, those are surprising responses for me anyway I guess.

Here's the thing about special files. They have an integer 'x' attached to
them which basically means "this file represents an index into an internal
kernel struct'.

Now if you are comfortable with the idea that a file, with a number
attached to its metadata, said number representing an index into an array
of structs, which has to work for all time and all kernels: then we're just
comfortable with different things. 'nuf said.

moving right along, when did /dev first appear?

On Wed, Feb 7, 2018 at 8:40 AM Nemo <cym224 at gmail.com> wrote:

> [top-post righted]
> > On 2/6/2018 9:06 PM, Dan Cross wrote:
> >
> > On Tue, Feb 6, 2018 at 8:48 PM, Dave Horsfall <dave at horsfall.org> wrote:
> >>
> >> On Wed, 7 Feb 2018, Greg 'groggy' Lehey wrote:
> >>>>
> >>>> V3 and earlier still *called* them special files, but it seems they
> were
> >>>> essentially just magic inode numbers (there was no physical file on
> disk,
> >>>> just any directory entry with the given inode would be the special
> file).
> >>>
> >>> Isn't that still the case?
> >>
> >> Wasn't that "devfs" (which Penguin/OS calls "udev")?  I've never grokked
> >> that concept.
> >
> > No. devfs was (is?) a pseudo-filesystem where only special files
> > corresponding to the devices enumerated by the kernel during
> > autoconfiguration are present. The contents are synthesized at boot time
> and
> > the filesystem is mounted at some canonical location (like /dev), but is
> > otherwise ephemeral. This is in contrast to the older /dev, which is
> usually
> > just a directory on the root filesystem, wherein one created a number of
> > device files that may (or may not) correspond to an actual hardware
> device
> > in the system (remember the old dance of, "cd /dev && ./MAKEDEV foo" when
> > you added a "foo" onto your system?). The inodes and directory entries
> for
> > those files actually exist in the disk-resident filesystem structures
> > (though of course data blocks aren't allocated to those files and the
> inode
> > doesn't refer to any data blocks).
> [...]
> >         - Dan C.
> >
> >
> On 7 February 2018 at 11:24, Arthur Krewat <krewat at kilonet.net> wrote:
> > medusa# mount | egrep '^/dev'
> > /devices on /devices read/write/setuid/devices/rstchown/dev=9640000 on
> Fri
> > Jan 19 16:33:07 2018
> [...]
> > SunOS medusa 5.11 11.3 i86pc i386 i86pc
>
> Further more (5.10 sun4u):
>
> File Systems                                           devfs(7FS)
>
> NAME
>      devfs - Devices file system
>
> DESCRIPTION
>      The devfs filesystem manages a name  space  of  all  devices
>      under  the Solaris operating environment and is mounted dur-
>      ing boot on the /devices name space.
>
>      The /devices name space is dynamic and reflects the  current
>      state  of  accessible  devices  under  the Solaris operating
>      environment. The names of all attached device instances  are
>      present under /devices.
>
>      The content under /devices is under the exclusive control of
>      the devfs filesystem and cannot be changed.
>
> N.
>
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