Re: [JOS-Kernel] Device as a digital resource

[Gilbert Carl Herschberger II]

At 09:26 PM 3/22/00 +0200, Al <[EMAIL PROTECTED]> wrote:
>Gilbert Carl Herschberger II wrote:
>
>> Oh, I see where you might be going. You're looking for something like
>> the /dev subdirectory on Linux/UNIX. Would you like every device to
>> have a node in the file subsystem?
>
>No, not at all. Actually, I hate the way Linux handles filesystems.
>Files on a disk simply have nothing to do with devices. I can only think
>of the filesystem as an extension to the device called "hard disk." I
>cannot understand why /dev is a subdirectory! It is only a subdirectory
>in a tree describing the computer hardware, *NOT* the filesystem!

I am glad to hear this. Like you, I dislike the way Linux handles devices.
Why is /dev a subdirectory? Linux is working from a 30+ year old design.
The design was invented before the world wide web and the invention of a
scheme-based resource identifier. The Linux community is looking for a
solution. They are working on more dynamic /dev directory, so that devices
are assigned as needed. They won't be assigned only when the kernel is
compiled.

Just like all other operating systems, JOS has to break through this
paradox. A few devices, like RAM, must exist before a file subsystem. And
since a device, like VMM, might use the file subsystem, a file subsystem
must exist before most devices.

Resource-oriented thinking dominates the software industry today.
Everything's a resource in resource-oriented thinking. I believe the device
subsystem has greatest priority. A device subsystem is required. A file
subsystem is not. With a URI scheme, devices can use other devices; but,
they cannot use the file subsystem. After the device subsystem has been
created, the file subsystem is created using previously existing devices.

When blocks of data are read by the BIOS from a floppy, it is
resource-oriented. When blocks of data are read by GRUB from a hard drive,
it is resource-oriented. When blocks of data are read by Etherboot from a
BOOTP/TFTP service, it is resource-oriented. When package files are read by
a primordial class loader, it is resource-oriented. There is no OS file
subsystem yet.

File-oriented thinking dominated the software industry until 1996.
Everything's a file in file-oriented thinking. In classic architecture
prior to JOS, the operating system is in a rush to get to the file
subsystem as fast as it possibly can. In Linux, the file subsystem exists
first. It is compiled into the kernel. It exists before any devices. At
first, only a placeholder is used for a devices in the /dev directory.
Then, any device can use the file subsystem because it already exists.

Because the file subsystem needs devices to read files, additional devices
are plugged into the file subsystem as they become available. Nodes of the
file subsystem are mounted.

For Linux compatibility, a file subsystem might return a device as an I/O
stream from the /dev directory.


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