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runtime-config-linux: Separate mknod from cgroups
With mknod entries in linux.devices and cgroups entries in linux.resources.devices. Background discussion in [1]. For specifying device cgroups independent of device creation. This makes it easy to distinguish between configs that call for cgroup adjustments (which have linux.resources entries) from those that don't. Without this split, folks interested in making that distinction would have to parse the device section to determine if it included cgroup changes. This will also make it easy to drop either portion (mknod [2] or cgroups [3]) independently of the other if the project decides to do so. Using seperate sections for mknod and cgroups also allows us to avoid the complicated validation rules needed for the combined format mknod/cgroup [4]. Now that there is a section specific to supplying devices, I shifted the default device listing over from config-linux [5]. The /dev/ptmx entry is a bit awkward, since it's not a device, but it seemed to fit better over here. But I would also be fine leaving it with the other mounts in config-linux. fileMode, uid, and gid are optional, because mknod(2) doesn't need them and specifies the handling when they aren't set [6,7]. Similarly, major/minor numbers are only required for S_IFCHR and S_IFBLK [6]. I've left off wording about required runtime behavior for unset values, because I'd rather address that with a blanket rule [8]. For the cgroup, access is optional because the kernel docs show an example that doesn't write an access field to the devices.deny file [9]. The current kernel docs don't go into much detail on this behavior (I expect unset and 'rwm' are equivalent), but if the kernel doesn't need a value written, the spec should get out of the way and allow users to not specify a value. The reference links are sorted into two blocks, with kernel-doc links sorted alphabetically followed by man pages sorted alphabetically by section. The cgroup link is new since 2016-01-13 [10]. [1]: https://groups.google.com/a/opencontainers.org/forum/#!topic/dev/y_Fsa2_jJaM Subject: Separate config entries for device mknod and cgroups? Date: Mon, 5 Oct 2015 12:46:55 -0700 Message-ID: <20151005194655.GN28418@odin.tremily.us> [2]: opencontainers#98 [3]: https://groups.google.com/a/opencontainers.org/forum/#!topic/dev/qWHoKs8Fsrk Subject: removal of cgroups from the OCI Linux spec Date: Wed, 28 Oct 2015 17:01:59 +0000 Message-ID: <CAD2oYtO1RMCcUp52w-xXemzDTs+J6t4hS5Mm4mX+uBnVONGDfA@mail.gmail.com> [4]: opencontainers#101 [5]: opencontainers#171 (comment) [6]: http://man7.org/linux/man-pages/man2/mknod.2.html#DESCRIPTION [7]: https://github.com/opencontainers/specs/pull/298/files#r51053835 [8]: opencontainers#285 (comment) [9]: https://kernel.org/doc/Documentation/cgroup-v1/devices.txt [10]: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=34a9304a96d6351c2d35dcdc9293258378fc0bd8 Signed-off-by: W. Trevor King <wking@tremily.us>
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