The DAP 5.6 specification (28-Mar-1980) does not appear to have much information concerning device mounting.

It's not clear how much DAP was designed to be concerned with such activities, but it would appear that it implicitly expects that any device that is available is usable.  There are some bits in the File Access Options (FOP) and Generic Device Characteristics (DEV) attributes that have some information concerning mounting, viz:

Attribute

Bit

Name

Meaning

FOP

13

FB$DMO

Rewind and dismount magnetic tape on close.

DEV

10

FB$MNT

Device is currently mounted.

DEV

11

FB$DMT

Device  is marked for dismount.

So assuming you are accessing a magnetic tape, you can request that it be rewound and dismounted when closed and you can get some information concerning mount status.

At this time of DAP design, large systems basically lived on tape and disk mounts, given the expense of the devices to actually read and write their respective media.  There was a cost for a mount, but if you were using a lot of space, it could pay to have your own media where you wouldn't get hit with the storage costs.

Mounting structures is also a well understood mechanism to provide additional access control granularity.

A "regulated" structure on Tops-20 can not be used unless it is first mounted by the user.  It may be spun up and online, but if it is regulated, you must mount it first.  This gives you the opportunity to put policy on the mount with an access control request.  At Columbia, nobody was allowed to mount the (regulated) staff structure (CU:, an RP07) unless they were staff.  Students were not allowed to mount anything.  Paying customers could mount non-domestic regulated structures.  I wrote the code for the 'Judge', our access control job (or ACJ) which did this as it required some hooks in Galaxy (Quasar and MOUNTR).

FAL is not subject to such ACJ policy because it specifically informs Tops-20 to by-pass mount counts.  So that's kind of a back door because you could use FAL to snoop around regulated structures, which is exactly what we didn't want to be happening.  It bothered me, but not enough for me to tell management that it should be addressed.

I was fixing a bug in FAL ANONYMOUS processing when I recalled this and it began to bother me more.  I don't want regulated structures being implicitly used.  My extended mode FTP server does not bypass mount counts and this is what keeps web crawlers from snooping through every file I have.  You have to explicitly know the structure name and request it with an SMNT verb which you can then put policy on.  So I scratched the itch and implemented a MOUNTING command with the following options:

PREVENTED is the most restricted, as a FAL job only has access to unregulated structures (which require no mounting).  So that's good.

AUTOMATIC maybe gets you the best of both worlds.  You can access online structures provided policy allows you to, elsewhere which means that users that expect to be able to mount structures will have this done for them.  I have yet to put in another command to restrict ANONYMOUS usage, in other words, forbid automatic mounting for ANONYMOUS.

Is my reading of DAP is close enough?  How do other DEC operating systems handle this?  I know VMS can handle disk and tape mounts, I forget about RSTS, RSX and RT.