[issue1537] null mount does not accept -o update

[Stathis Kamperis (via DragonFly issue tracker)]

Stathis Kamperis <ekamperi at gmail.com> added the comment:

Salute.

I have a patch here:
http://leaf.dragonflybsd.org/~beket/updnull.diff

I have tested it extensively and it works. Stuff I tried:

1. Switching between ro/rw in a local null mount.
And verified read-onlyness by trying to touch a file.

2. Switching between ro/rw in stacks of local null mounts.
And verified read-onlyness by trying to touch a file.

3. Switching between ro/rw in a NFS exported null mount.
Specifically, /pfs/@@-1:00004 was null mounted on /home. And /home was NFS
shared with dfly being the server. NFS client was opensolaris build 126. I was
able to write from osol when /home was exported as read-write, and failed to do
so when it was exported as read-only. Client correctly reported that fs was
read-only. And so did mount(8) in the server side.

I can provide copy/pastes from sessions, upon request. But better, fetch the
patch and try it yourself :)

This http://leaf.dragonflybsd.org/~beket/mountnull.png shows some preliminary
tests I did (they do not cover switching back to ro from rw, or 3.)

Best regards,
Stathis Kamperis

----------
assignedto:  -> Beket
nosy: +Beket
priority:  -> feature
status: chatting -> testing

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