Re: exact semantics of union mounts (and TRYEMULROOT)

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

[one message]
>>> Union mounts [...]
>> I don't think so, directory ops all happen at the upper level (or
>> nowhere).
> I don't think that's what Plan 9 does [...]

[another message]
>> Also, the 5.2 mount(8) manpage says
>>              union       [...]
>> [...], it sounds to me as though the above preempts most of your
>> questions.
> No, it doesn't.  Union mounts were invented by Plan 9 and the Plan 9
> behavior is the normative reference.

Then why are you asking here?  Why not ask on a Plan 9 list?

I see no reason NetBSD's union mounts have to, nor even should, be
identical, or even as close to identical as the rest of the system can
support, to Plan 9's union mounts.

Indeed, union mounts in NetBSD are old enough (1.4T, from about the
turn of the millennium, has both mount -o union and mount -t union!)
that I think changing the existing NetBSD semantics to match Plan 9's
would be a bad idea.  (If you want to add mount -o plan9union and/or
mount -t plan9union, that's a separate question.)

> Vague and ambiguous statements in our man pages aren't particularly
> helpful.

Denigratory adjectives aside (I found the statements I quoted neither
vague nor ambiguous), that depends on whether you are trying to
suddenly (as far as users are concerned) change decade-plus-old
semantics to match some relatively obscure OS most of them have likely
never heard of, or whether you're trying to fix the implementation we
have of those decade-plus-old semantics.  Your first email left me
thinking it was the latter.  If it's actually the former, most of what
I wrote is irrelevant and I have little-to-nothing to say on the
subject, since I'm not familiar with the Plan 9 semantics.

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