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Message-ID: <20140915203844.GA14761@nixos.hsd1.nh.comcast.net> Date: Mon, 15 Sep 2014 16:38:44 -0400 From: Shea Levy <shea@...alevy.com> To: Seth Forshee <seth.forshee@...onical.com> Cc: linux-kernel@...r.kernel.org, lxc-devel@...ts.linuxcontainers.org Subject: Re: [RFC PATCH 0/2] Loop device psuedo filesystem Hi, I wanted to test these patches (to support creating and filling a disk image containing a btrfs filesystem and several subvolumes as an unprivileged user), but the build fails due to what looks like a missing loopfs.c in fs/loopfs (or alternatively an erroneous line in fs/loopfs/Makefile). I built based off of 3.17-rc5. ~Shea On Tue, May 27, 2014 at 11:58:54PM +0200, Seth Forshee wrote: > I'm posting these patches in response to the ongoing discussion of loop > devices in containers at [1]. > > The patches implement a psuedo filesystem for loop devices, which will > allow use of loop devices in containters using standard utilities. Under > normal use a loopfs mount will initially contain a single device node > for loop-control which can be used to request and release loop devices. > Any devices allocated via this node will automatically appear in that > loopfs mount (and in devtmpfs) but not in any other loopfs mounts. > CAP_SYS_ADMIN in the userns of the process which performed the mount is > allowed to perform privileged loop ioctls on these devices. > > Alternately loopfs can be mounted with the hostmount option, intended > for mounting /dev/loop in the host. This is the default mount for any > devices not created via loop-control in a loopfs mount (e.g. devices > created during driver init, devices created via /dev/loop-control, etc). > This is only available to system-wide CAP_SYS_ADMIN. > > I still have some testing to do on these patches, but they work at > minimum for simple use cases. It's possible to use an unmodified losetup > if it's new enough to know about loop-control, with a couple of caveats: > > * /dev/loop-control must be symlinked to /dev/loop/loop-control > * In some cases losetup attempts to use /dev/loopN when the device node > is at /dev/loop/N. For example, 'losetup -f disk.img' fails. > > Device nodes for loop partitions are not created in loopfs. These > devices are created by the generic block layer, and the loop driver has > no way of knowing when they are created, so some kind of hook into the > driver will be needed to support this. > > Thanks, > Seth > > [1] http://article.gmane.org/gmane.linux.kernel/1703988 > > Seth Forshee (2): > loop: Add loop filesystem > loop: Permit priveleged operations within user namespaces > > drivers/block/loop.c | 137 +++++++++++++---- > drivers/block/loop.h | 2 + > fs/Makefile | 1 + > fs/loopfs/Makefile | 6 + > fs/loopfs/inode.c | 360 +++++++++++++++++++++++++++++++++++++++++++++ > include/linux/loopfs.h | 53 +++++++ > include/uapi/linux/magic.h | 1 + > 7 files changed, 535 insertions(+), 25 deletions(-) > create mode 100644 fs/loopfs/Makefile > create mode 100644 fs/loopfs/inode.c > create mode 100644 include/linux/loopfs.h > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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