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Date:      Fri, 22 Nov 2019 15:16:02 +0100
From:      Jan Behrens <jbe-mlist@magnetkern.de>
To:        Borja Marcos <borjam@sarenet.es>
Cc:        Martin Simmons <martin@lispworks.com>, freebsd-fs@freebsd.org
Subject:   Re: ZFS snapdir readability (Crosspost) OT: mount -t zfs for snapshots
Message-ID:  <20191122151602.c84f717ca3d1a9bb6a66aab8@magnetkern.de>
In-Reply-To: <B708E4EB-0387-47B2-B03F-A2134A3F3169@sarenet.es>
References:  <20191107004635.c6d2e7d464d3d556a0d87465@magnetkern.de> <CAOtMX2huHZcXHH%2B=3Bx7hX_p9udJ2acOX%2BZL8vW=pjqbe6mOAA@mail.gmail.com> <e2eecef7-21b6-0ff2-b259-71421b7d097c@sentex.net> <9B22AD46-BE87-4305-9638-74D23AD4C8CA@sarenet.es> <cfcc12dd-e9eb-5a98-a031-ab18436a2dd3@sentex.net> <261FE331-EC5C-48C8-9249-9BCBF887CE38@sarenet.es> <913f7040-6e38-452d-6187-e17fae63b652@sentex.net> <20191120144041.7f916360dc0c69bf509c9bd1@magnetkern.de> <AEF4CA02-36B3-42FC-BE92-14DF0AF99540@sarenet.es> <20191120163437.691abd369ab9c0a6d7d45ff2@magnetkern.de> <CF38B478-3638-4C18-B69F-E589DE9BBB95@sarenet.es> <20191120175803.03401c3316fe756cc46f79f1@magnetkern.de> <3C5DC6DD-C44B-41EE-B7AB-6D8F94E43174@sarenet.es> <201911211259.xALCxShX008743@higson.cam.lispworks.com> <462E2C53-2490-4B8C-BB54-BCE8B75BAEB0@sarenet.es> <201911211630.xALGUT5Z010705@higson.cam.lispworks.com> <B708E4EB-0387-47B2-B03F-A2134A3F3169@sarenet.es>

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On Fri, 22 Nov 2019 09:09:52 +0100
Borja Marcos <borjam@sarenet.es> wrote:

> > On 21 Nov 2019, at 17:30, Martin Simmons <martin@lispworks.com> wrote:
> > 
> >> I’ve never seen that and, indeed, on FreeBSD 12.1 it’s not possible. Or I am terribly
> >> sloppy today!
> >> 
> >> Did I miss anything? Is it a new ZFS on Linux feature?
> >> 
> >> root@micro1:~ # mount -t zfs -o ro pool/dataset@snapshot /mnt
> >> mount: unpul/wwwnfsen@antesinst: Device busy
> >> root@micro1:~ # 
> > 
> > It looks like unpul/wwwnfsen@antesinst is already mounted -- probably in .zfs :-)
> 
> (This is a bit of off-topic now, the behavior of mount -t zfs)
> 
> Yep, it’s only uglier!
> 
> Whenever you access any of the directories below .zfs/snapshot the snapshot
> is automagically mounted. It’s also sort of invisible except when you run “mount -v”. In that
> case those snapshot mounts are visible. You can also unmount them.

I also just confirmed that once I manually mount a snapshot, I can't
access it through .zfs/snapshot anymore. Of course, this is doesn't
help with solving the original problem because in order to prohibit
snapshot access for non-privileged users, it would require all
snapshots to be mounted atomically at the same time the associated
filesystem is mounted.

> [...]
> 
> Borja.

Regards,
Jan




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