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Date:      Fri, 18 Sep 2015 13:54:29 +0800
From:      Julian Elischer <julian@freebsd.org>
To:        Kevin Day <toasty@dragondata.com>, Jan Bramkamp <crest@rlwinm.de>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: Neutered devices in jails (per FS flag?)
Message-ID:  <55FBA715.707@freebsd.org>
In-Reply-To: <7D445BFC-AB18-4EAD-8065-F0A934B1A479@dragondata.com>
References:  <E0C9157B-0FB7-4B2B-9BA2-5779DA7877FF@dragondata.com> <55F99F5A.302@rlwinm.de> <7D445BFC-AB18-4EAD-8065-F0A934B1A479@dragondata.com>

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On 9/17/15 12:58 AM, Kevin Day wrote:
>> On 16/09/15 18:30, Kevin Day wrote:
>>> We’re currently using jails to allow servers to copy backups of themselves to a central backup server. The problem we’re having is with mknod/devices. Currently jails don’t allow device files to be created, which makes sense - you don’t want them to be able to bypass the jail by opening /dev/kmem or something. We want jails to be able to create device files, just not be able to open/use them.
>>>
>>> Has anyone given any thought to changing this behavior? Allowing jails to create/manipulate device files, but not actually opening them? I.e. instead of returning EPERM on creating the device, instead return EPERM on opening it? This would likely need to be a filesystem flag, because jails still require some devices to work (a separate devfs mount or something). We could make the jail’s /dev read only or use devfs so those devices still work, but have the parent jail directory with a “noopendev” flag or something similar.
>>>
>>> Has anyone gone down this path before?
>> There is no reason to backup device files on FreeBSD because FreeBSD uses a dynamic devfs. Backup the devfs rules and devfs.conf instead of the device files.
> We’re backing up non-FreeBSD systems, as well as some software that creates its own devices inside a mini-chroot it needs to run.
you can't create device files under FreeBSD...... well, you can make 
the nodes I guess but they don't connect to any device..
they only exist to allow them to be exported through NFS as far as I know.

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