Date: Fri, 15 Sep 2017 19:27:52 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Edward Napierala <trasz@freebsd.org> Cc: Kirk McKusick <mckusick@mckusick.com>, freebsd-fs <freebsd-fs@freebsd.org>, Andriy Gapon <avg@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: mount / unmount and mountcheckdirs() Message-ID: <20170915162752.GX78693@kib.kiev.ua> In-Reply-To: <CAFLM3-oEvMxvTNL7cRPrQsNonxe89NFXY_yirhWcHprrvaem2Q@mail.gmail.com> References: <134c7c6e-f4f1-ef38-cc50-0e56c27c9fb8@FreeBSD.org> <201709150314.v8F3Ea6B085072@chez.mckusick.com> <20170915092001.GK78693@kib.kiev.ua> <CAFLM3-rqg9Pso636Y3Vm6JT0WxWossEfvnsMmmAbC-jEkvyS7Q@mail.gmail.com> <20170915103037.GM78693@kib.kiev.ua> <CAFLM3-oPXg1we2f6comaJCyUQU3OMuSR6YgupQD3qDMbM5o%2B=g@mail.gmail.com> <20170915110033.GO78693@kib.kiev.ua> <CAFLM3-q8eUPRwBOJU-in-syb3vgBnNm23aoJ0XCA7=C=BQkT7A@mail.gmail.com> <20170915114533.GS78693@kib.kiev.ua> <CAFLM3-oEvMxvTNL7cRPrQsNonxe89NFXY_yirhWcHprrvaem2Q@mail.gmail.com>
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On Fri, Sep 15, 2017 at 05:06:10PM +0100, Edward Napierala wrote: > 2017-09-15 12:45 GMT+01:00 Konstantin Belousov <kostikbel@gmail.com>: > > > On Fri, Sep 15, 2017 at 12:31:05PM +0100, Edward Napierala wrote: > > > 2017-09-15 12:00 GMT+01:00 Konstantin Belousov <kostikbel@gmail.com>: > > > > > > > On Fri, Sep 15, 2017 at 11:49:17AM +0100, Edward Napierala wrote: > > > > > 2017-09-15 11:30 GMT+01:00 Konstantin Belousov <kostikbel@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@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@v2:~]% cd /media/md0 > > > > > > > [trasz@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@v2:/media/md0]% ls > > > > > > > [trasz@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@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@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@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 ? > > > > > > > > > > Yes. > > > > > > > > > > If yes, then this demonstration indeed proves that autofs behaves as > > > > intended on mount. > > > > > > > > > > Exactly. And, from what I understand, that would break if > > mountcheckdirs() > > > got removed from the mount path. > > > > Even for autofs ? Don't autofs postpone lookup() completion until the > > mount occurs ? > > > > It does, and that case might work - I'm not sure, but it might. But what > happens afterwards, after the syscall that triggered the mount completes? > You would still have a shell with cwd in that dir, now covered by another > filesystem. Autofs doesn't do anything to "lift" the process to the newly > mounted filesystem root. The change of the current directory should have already triggered the action, because it was preceeded by lookup. At least this is my understanding of the flow.
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