Unprivileged lxc container fails to start due to error mounting proc

== SRU Justification ==

Impact: Unprivileged lxc containers fail to start whenever a filesystem is mounted on /proc/fs/nfsd.

Fix: Cherry pick upstream commit d443b9fd56e85c0e58d10b75cf5eb38e0b2c4c02.

Regression Potential: This commit modifies proc_register so that callers must set the proc_fops and/or proc_iops before calling rather that proc_register assigning them based on the type of inode passed. All call sites in 3.19 match exactly with those upstream at the time the patch was merged, except for proc_create_mount_point which is the call site causing this issue. Which is to say that there is no functional change for any proc inodes except for the ones which can cause this problem, therefore there should be little potential for regression.

---

Unprivileged lxc containers fail to start in some instances under vivid:

      lxc-start 1448306932.775 ERROR lxc_utils - utils.c:safe_mount:1686 - Operation not permitted - Failed to mount proc onto /usr/lib/x86_64-linux-gnu/lxc/proc
      lxc-start 1448306932.775 ERROR lxc_conf - conf.c:lxc_mount_auto_mounts:828 - Operation not permitted - error mounting proc on /usr/lib/x86_64-linux-gnu/lxc/proc flags 14

The failure is caused by the backport of 7236c85e1be51a9e25ba0f6e087a66ca89605a49 "mnt: Update fs_fully_visible to test for permanently empty directories." The backport itself is correct but some of its assumptions are not met to do a change which happened after 3.19. This causes /proc/fs/nfsd to fail the "directory is permanently empty" test, and when the nfsd fs another filesystem is mounted on that directory it causes the mount of proc in the container to fail. The fix is to bakcport d443b9fd56e85c0e58d10b75cf5eb38e0b2c4c02 "gut proc_register() a bit" as well.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: linux-image-3.19.0-33-generic 3.19.0-33.38
ProcVersionSignature: User Name 3.19.0-33.38-generic 3.19.8-ckt7
Uname: Linux 3.19.0-33-generic x86_64
AlsaDevices:
 total 0
 crw-rw---- 1 root audio 116, 1 Nov 23 21:22 seq
 crw-rw---- 1 root audio 116, 33 Nov 23 21:22 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.17.2-0ubuntu1.8
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
Date: Mon Nov 23 21:24:16 2015
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lsusb: Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
PciMultimedia:

ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB:

ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.19.0-33-generic root=UUID=63d8816d-53d7-4318-b873-2cfe367b957a ro console=tty1 console=ttyS0
RelatedPackageVersions:
 linux-restricted-modules-3.19.0-33-generic N/A
 linux-backports-modules-3.19.0-33-generic N/A
 linux-firmware 1.143.7
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 01/01/2011
dmi.bios.vendor: Bochs
dmi.bios.version: Bochs
dmi.chassis.type: 1
dmi.chassis.vendor: Bochs
dmi.modalias: dmi:bvnBochs:bvrBochs:bd01/01/2011:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-trusty:cvnBochs:ct1:cvr:
dmi.product.name: Standard PC (i440FX + PIIX, 1996)
dmi.product.version: pc-i440fx-trusty
dmi.sys.vendor: QEMU