[Info-vax] Filesystems on VMS, was: Re: Command Procedure Pipe output to a variable

[Simon Clubley]

On 2021-09-22, Lawrence D?Oliveiro <lawrencedo99 at gmail.com> wrote:
> On Wednesday, September 8, 2021 at 5:58:13 AM UTC+12, Simon Clubley wrote:
>> Linux has also recently acquired the ability to mount filesystems over 
>> SSH, but you are unlikely to ever see that in VMS due to VMS's utter 
>> inability to support userspace filesystems. 
>
> I think how that actually works is that Linux has long implemented filesystems through a VFS indirection layer, which is how it?s able to handle all kinds of different volume formats (e.g. DOS FAT, ISO 9660, Apple HFS+, Windows NTFS, old IRIX XFS, MINIX etc). But these would normally all require in-kernel drivers. So FUSE (?Filesystem in Userspace?) implements a single generic in-kernel filesystem driver on top of VFS, that offers an API to userland processes. And this is used by a whole bunch of additional packages like sshfs, mtpfs, winregfs etc. In fact, the FUSE version of NTFS is actually more full-featured than the kernel version.

Yes, that's how it works.

VMS has absolutely nothing like the FUSE support Linux does.

It does have ACPs to handle some _devices_ in process context, but they
are nothing like FUSE and ACPs are very ugly to implement anyway.
Also, good luck finding any public documentation for writing an ACP.

VMS doesn't even have anything like the filesystem kernel plugin modules
that you see in Linux and elsewhere. The VMS architecture simply isn't
setup to support anything like that.

BTW, did you know that once you load a device driver into VMS, you
can't even remove it unlike what you can do elsewhere ?

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.