Re: Add a mountlist iterator (round 2)

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

> On 5. Apr 2017, at 05:14, Chuck Silvers <chuq%chuq.com@localhost> wrote:
> 
> have you considered a callback-based interface where the loop
> is inside the iteration API rather than in the caller?
> the vfs_busy/unbusy could also be hidden in the iteration API
> so that the callback would not need need to worry about it at all.
> 
> I looked at how the iteration stuff is used in your patches
> (the first one, I haven't looked in the latest one in detail)
> and it looks like most of users would be fine with not being able
> to do anything after vfs_unbusy().  the one place that really does
> want to do more after vfs_unbusy() is vfs_unmountall1(),
> but that could be rewritten to loop unmounting the last mount
> in the list until they're all gone.
> 
> I think this would further simplify most (if not all) cases of
> mountlist iteration.

Good hint.  Prepared a partial implementation of

int
mountlist_iterate(int (*cb)(struct mount *, void *), void *arg)

to take "mp" busy and call "cb(mp, arg)" for all mounted file systems.

A non waiting variant "mountlist_iterate_nowait()" could be added
when it gets needed.

Changed "vfs_unmountall1()" to retrieve mounts in descending
generation order which has the additional benefit that we don't
need reverse traversals any more.

Diffs are here: https://www.netbsd.org/~hannken/ml_iterator2a/

I prefer this API, opinions?

--
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig (Germany)