[TUHS] Device special files

[Nemo]

[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.