mount / unmount and mountcheckdirs()

[Konstantin Belousov]

On Fri, Sep 15, 2017 at 11:49:17AM +0100, Edward Napierala wrote:
> 2017-09-15 11:30 GMT+01:00 Konstantin Belousov <kostikbel at gmail.com>:
> 
> > On Fri, Sep 15, 2017 at 11:08:31AM +0100, Edward Napierala wrote:
> > > 2017-09-15 10:20 GMT+01:00 Konstantin Belousov <kostikbel at gmail.com>:
> > > > I believe that the current autofs does not allow a process to get into
> > > > this situation at all.
> > > >
> > >
> > > It does.  For example:
> > >
> > > [trasz at v2:~]% cd /media/md0
> > > [trasz at v2:/media/md0]% mount
> > > /dev/ada0s1a on / (ufs, local, noatime, journaled soft-updates)
> > > devfs on /dev (devfs, local, multilabel)
> > > map -hosts on /net (autofs)
> > > map -media on /media (autofs)
> > > [trasz at v2:/media/md0]% ls
> > > [trasz at v2:/media/md0]% mount
> > > /dev/ada0s1a on / (ufs, local, noatime, journaled soft-updates)
> > > devfs on /dev (devfs, local, multilabel)
> > > map -hosts on /net (autofs)
> > > map -media on /media (autofs)
> > > /dev/md0 on /media/md0 (ufs, local, noatime, nosuid, automounted)
> > >
> > > Getting rid of mountcheckdirs() in the unmount path should be fine, I
> > think.
> > How the example proves that mountcheckdirs() can be removed ?
> 
> 
> In the unmount path?  It doesn't; I just don't think autofs would be
> affected,
> since having a current working directory in a mountpoint prevents the
> unmount
> (unless it's forced).
> 
> In the mount path?  See below.
> 
> 
> > How can
> > we see which directory content was printed by ls, the covered or mounted ?
> >
> 
> Well, it would be pretty useless if you got the covered directory.
This is exactly what is being discussed.

> But ok, here's
> a better example, one that actually shows that:
> 
> [trasz at v2:/media/md0]% mount
> /dev/ada0s1a on / (ufs, local, noatime, journaled soft-updates)
> devfs on /dev (devfs, local, multilabel)
> map -hosts on /net (autofs)
> map -media on /media (autofs)
> [trasz at v2:/media/md0]% ls -al
> total 9
> drwxr-xr-x  3 root  wheel     512 Sep 10 10:16 .
> drwxr-xr-x  3 root  wheel     512 Sep  8 11:42 ..
> drwxrwxr-x  2 root  operator  512 Sep 10 10:16 .snap
> [trasz at v2:/media/md0]% mount
> /dev/ada0s1a on / (ufs, local, noatime, journaled soft-updates)
> devfs on /dev (devfs, local, multilabel)
> map -hosts on /net (autofs)
> map -media on /media (autofs)
> /dev/md0 on /media/md0 (ufs, local, noatime, nosuid, automounted)
> 
> Notice the .snap/ directory; it's an empty UFS filesystem.
And the .snap is from the /dev/md0 volume, right ?
If yes, then this demonstration indeed proves that autofs behaves as
intended on mount.