From: Seth Forshee <seth.forshee@canonical.com>
To: LXC development mailing-list <lxc-devel@lists.linuxcontainers.org>
Cc: Jens Axboe <axboe@kernel.dk>,
Serge Hallyn <serge.hallyn@canonical.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org,
James Bottomley <James.Bottomley@HansenPartnership.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [lxc-devel] [RFC PATCH 00/11] Add support for devtmpfs in user namespaces
Date: Fri, 16 May 2014 10:43:38 -0500 [thread overview]
Message-ID: <20140516154338.GB23902@ubuntu-hedt> (raw)
In-Reply-To: <1400254108.3540.5.camel@canyon.ip6.wittsend.com>
On Fri, May 16, 2014 at 11:28:28AM -0400, Michael H. Warfield wrote:
> On Fri, 2014-05-16 at 09:06 -0500, Seth Forshee wrote:
> > On Thu, May 15, 2014 at 09:35:32PM -0700, Greg Kroah-Hartman wrote:
> > > On Fri, May 16, 2014 at 01:49:59AM +0000, Serge Hallyn wrote:
> > > > > I think having to pick and choose what device nodes you want in a
> > > > > container is a good thing. Becides, you would have to do the same thing
> > > > > in the kernel anyway, what's wrong with userspace making the decision
> > > > > here, especially as it knows exactly what it wants to do much more so
> > > > > than the kernel ever can.
> > > >
> > > > For 'real' devices that sounds sensible. The thing about loop devices
> > > > is that we simply want to allow a container to say "give me a loop
> > > > device to use" and have it receive a unique loop device (or 3), without
> > > > having to pre-assign them. I think that would be cleaner to do using
> > > > a pseudofs and loop-control device, rather than having to have a
> > > > daemon in userspace on the host farming those out in response to
> > > > some, I don't know, dbus request?
> > >
> > > I agree that loop devices would be nice to have in a container, and that
> > > the existing loop interface doesn't really lend itself to that. So
> > > create a new type of thing that acts like a loop device in a container.
> > > But don't try to mess with the whole driver core just for a single type
> > > of device.
>
> > No matter what I don't think we get out of this without driver core
> > changes, whether this was done in loop or by creating something new.
> > Not unless the whole thing is punted to userspace, anyway.
>
> > The first problem is that many block device ioctls check for
> > CAP_SYS_ADMIN. Most of these might not ever be used on loop devices, I'm
> > not really sure. But loop does at minimum support partitions, and to get
> > that functionality in an unprivileged container at least the block layer
> > needs to know the namespace which has privileges for that device.
>
> Woa! Time out... Sorry, this will be an off topic aside.
>
> Loop devices support partitions? I'd love to know how that works. I've
> tried several times in the past to do that but it's failed every time.
> I haven't been able to find any how-to in the past. This article was
> just a couple of years ago (after the last time I tried this):
>
> http://madduck.net/blog/2006.10.20:loop-mounting-partitions-from-a-disk-image/
>
> This guy didn't use partitions directly but used the offset to the
> mount, which is what I had to use. Everything I found always referred
> to using mount offsets in order to mount partitions within a loop
> device.
It's controlled by the loop.max_part module parameter. It defaults to 0,
which means no partition support. For any value > 0 max_part will be the
maximum available partition number, after rounding it up to the nearest
power of 2 minus 1 (so max_part=5 gives you up to 8 partitions,
max_part=8 gives you up to 16, etc).
next prev parent reply other threads:[~2014-05-16 15:43 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-14 21:34 [RFC PATCH 00/11] Add support for devtmpfs in user namespaces Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 01/11] driver core: Assign owning user namespace to devices Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 02/11] driver core: Add device_create_global() Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 03/11] tmpfs: Add sub-filesystem data pointer to shmem_sb_info Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 04/11] ramfs: Add sub-filesystem data pointer to ram_fs_info Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 05/11] devtmpfs: Add support for mounting in user namespaces Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 06/11] drivers/char/mem.c: Make null/zero/full/random/urandom available to " Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 07/11] block: Make partitions inherit namespace from whole disk device Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 08/11] block: Allow blkdev ioctls within user namespaces Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 09/11] misc: Make loop-control available to all " Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 10/11] loop: Assign devices to current_user_ns() Seth Forshee
2014-05-14 21:34 ` [RFC PATCH 11/11] loop: Allow priveleged operations for root in the namespace which owns a device Seth Forshee
2014-05-23 5:48 ` Marian Marinov
2014-05-26 9:16 ` Seth Forshee
2014-05-26 15:32 ` [lxc-devel] " Michael H. Warfield
2014-05-26 15:45 ` Seth Forshee
2014-05-27 1:36 ` Serge E. Hallyn
2014-05-27 2:39 ` Michael H. Warfield
2014-05-27 7:16 ` Seth Forshee
2014-05-27 13:16 ` Serge Hallyn
2014-05-15 1:32 ` [RFC PATCH 00/11] Add support for devtmpfs in user namespaces Greg Kroah-Hartman
2014-05-15 2:17 ` [lxc-devel] " Michael H. Warfield
2014-05-15 3:15 ` Seth Forshee
2014-05-15 4:00 ` Greg Kroah-Hartman
2014-05-15 13:42 ` Michael H. Warfield
2014-05-15 14:08 ` Greg Kroah-Hartman
2014-05-15 17:42 ` Serge Hallyn
2014-05-15 18:12 ` Seth Forshee
2014-05-15 22:15 ` Greg Kroah-Hartman
2014-05-16 1:42 ` Michael H. Warfield
2014-05-16 7:56 ` Richard Weinberger
2014-05-16 19:20 ` James Bottomley
2014-05-16 19:42 ` Michael H. Warfield
2014-05-16 19:52 ` [lxc-devel] Mount and other notifiers, was: " James Bottomley
2014-05-16 20:04 ` Michael H. Warfield
2014-05-16 1:49 ` [lxc-devel] " Serge Hallyn
2014-05-16 4:35 ` Greg Kroah-Hartman
2014-05-16 14:06 ` Seth Forshee
2014-05-16 15:28 ` Michael H. Warfield
2014-05-16 15:43 ` Seth Forshee [this message]
2014-05-16 18:57 ` Greg Kroah-Hartman
2014-05-16 19:28 ` James Bottomley
2014-05-16 20:18 ` Seth Forshee
2014-05-20 0:04 ` Eric W. Biederman
2014-05-20 1:14 ` Michael H. Warfield
2014-05-20 14:18 ` Serge Hallyn
2014-05-20 14:21 ` Seth Forshee
2014-05-21 22:00 ` Eric W. Biederman
2014-05-21 22:33 ` Serge Hallyn
2014-05-23 22:23 ` Eric W. Biederman
2014-05-28 9:26 ` Seth Forshee
2014-05-28 13:12 ` Serge E. Hallyn
2014-05-28 20:33 ` Eric W. Biederman
2014-05-18 2:42 ` Serge E. Hallyn
2014-05-17 4:31 ` Eric W. Biederman
2014-05-17 16:01 ` Seth Forshee
2014-05-18 2:44 ` Serge E. Hallyn
2014-05-19 13:27 ` Seth Forshee
2014-05-20 14:15 ` Serge Hallyn
2014-05-20 14:26 ` Serge Hallyn
2014-05-17 12:57 ` Michael H. Warfield
2014-05-15 18:25 ` Richard Weinberger
2014-05-15 19:50 ` Serge Hallyn
2014-05-15 20:13 ` Richard Weinberger
2014-05-15 20:26 ` Serge E. Hallyn
2014-05-15 20:33 ` Richard Weinberger
2014-05-19 20:22 ` Andy Lutomirski
2014-05-20 14:19 ` Serge Hallyn
2014-05-23 8:20 ` Marian Marinov
2014-05-23 13:16 ` James Bottomley
2014-05-23 16:39 ` Andy Lutomirski
2014-05-24 22:25 ` Serge Hallyn
2014-05-25 8:12 ` James Bottomley
2014-05-25 22:24 ` Serge E. Hallyn
2014-05-28 7:02 ` James Bottomley
2014-05-28 13:49 ` Serge Hallyn
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