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Date:      Fri, 30 Apr 2021 20:04:13 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 255061] [PATCH] Proof of concept nested mounts for automounter -hosts map
Message-ID:  <bug-255061-227-69fQASnW7y@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-255061-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-255061-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D255061

Edward Tomasz Napierala <trasz@FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |trasz@FreeBSD.org

--- Comment #1 from Edward Tomasz Napierala <trasz@FreeBSD.org> ---
Hello, and thank you!  I'm really happy to see work being done on what's
probably the main piece of functionality missing from our current automount=
er.

I like the approach you've taken.  Regarding the unmounting problem (notes.=
txt,
#1): I agree about it being the primary missing piece.  I'm not sure I like=
 the
idea of recursive unmounts (or recursive anything) in the kernel.  I wonder,
though, using your example:

/net              (autofs)
/net/foo/a        (nfs, automounted)
/net/foo/a/b      (autofs, automounted)
/net/foo/a/x      (autofs, automounted)
/net/foo/a/b/c    (nfs, automounted)

It should be technically possible (using 'umount -f') to forcibly unmount
/net/foo/a despite /net/foo/a/b and its siblings still being mounted, and
unmount the (now unaccessible) submounts afterwards.  Thus, it might be
possible to add a flag to the unmount(2) syscall to make it to fail the
unmount(2) syscall with EBUSY if there are still vnodes open, except the on=
es
with autofs submounts mounted over it?

Regarding notes.txt, #4: I think autofs(5) doesn't stop just the initial th=
read
that triggered the mount, but also all other attempts to access the same
mountpoint - the threads should "queue up" on the automountd request struct=
ure,
and get unpaused after automountd signals the mount is done.

As for all the other points, I generally agree, or just have nothing to add=
 at
the moment.  I've only skimmed through the source for now, but don't have a=
ny
major suggestions yet apart from a fairly general ones, eg that it might ma=
ke
sense to use tree(3) macros, or not check for NULL before free(3).

I wonder, should we perhaps move this discussion to http://reviews.FreeBSD.=
org?

Thanks again!

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