** Also affects: cloud-utils (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: cloud-utils (Ubuntu Xenial)
Status: New => In Progress
** Description changed:
+ === Begin SRU Template ===
+ [Impact]
+ The 16.10 kernel dropped a legacy kernel module alias that allowed usage of
+ the 'overlay' filesystem via name 'overlayfs'. This broke overlayroot as
+ it explicitly tried to to use 'overlayfs' by name in loading of modules and
+ also in entry in /etc/fstab.
+
+ Without this fix, overlayroot will simply not work on any upstream kernel
+ or Ubuntu kernel of 16.10 (yakkety) or later.
+
+ [Test Case]
+ Note, not applying proposed as shown in step 3 below will recreate failure.
+
+ 1.) Start an instance of a cloud image.
+
+ 2.) get a suitable 4.8 kernel
+ On 16.10 or later, this is already done. On 16.04, we currently need to
+ install the kernel team's PPA to get one.
+
+ $ sudo apt-add-repository -y ppa:canonical-kernel-team/ppa
+ $ sudo apt update -q && sudo apt install -y linux-virtual-hwe-16.04-edge
</dev/null
+
+ 3.) Enable proposed and install overlayroot to show fix.
+ $ rel=$(lsb_release -sc)
+ $ echo "deb http://archive.ubuntu.com/ubuntu $rel-proposed main" |
+ $ sudo tee /etc/apt/sources.list.d/proposed.list
+ $ sudo apt update -qy && sudo apt install -qy overlayroot </dev/null
+ $ dpkg-query --show overlayroot
+ overlayroot 0.27ubuntu1.3
+
+ 4.) Enable overlayroot and reboot
+ # remove the cloud-init written mount options for /dev/vdb
+ # if we do not do this, then /mnt ends up not mounted due to ordering.
+ $ sudo sed -i.dist
s/,x-systemd.requires=cloud-init.service,comment=cloudconfig// /etc/fstab
+ $ echo "overlayroot=tmpfs" | sudo tee /etc/overlayroot.local.conf
+ $ sudo reboot
+
+ 5.) log back in and look around.
+ a.) check that 'overlayroot' is in /proc/mounts
+ $ awk '$1 == "overlayroot" { print $0 }' /proc/mounts
+ overlayroot / overlay
rw,relatime,lowerdir=/media/root-ro,upperdir=/media/root-rw/overlay,workdir=/media/root-rw/overlay-workdir/_
0 0
+
+ b.) check /run/initramfs/overlayroot.log
+ $ grep success /run/initramfs/overlayroot.log
+ [success]: configured root with 'tmpfs' using overlay per
/dev/vda1/etc/overlayroot.local.conf
+
+ 6.) try with recurse disabled
+
+ Assuming you're on the same system and in an overlayroot, to change the
+ file necessary, we use overlayroot-chroot.
+
+ $ echo overlayroot=tmpfs:recurse=0 | sudo overlayroot-chroot tee
/etc/overlayroot.local.conf
+ $ sudo reboot
+
+ 7.) log back in and look around.
+ This time the /mnt should not have overlay on it.
+
+ $ grep vdb /proc/mounts
+ /dev/vdb /mnt ext4 rw,relatime,data=ordered 0 0
+ $ grep overlay /proc/mounts
+ overlayroot / overlay
rw,relatime,lowerdir=/media/root-ro,upperdir=/media/root-rw/overlay,workdir=/media/root-rw/overlay-workdir/_
0 0
+ $ cat /etc/overlayroot.local.conf
+ overlayroot=tmpfs:recurse=0
+
+ [Regression Potential]
+ The most likely regression is just in failure for overlayroot to work.
+ That was the case 100% of the time on any kernel without 'overlayfs'
+ filesystem, so this can't really make things worse from that perspective.
+
+ Some of the code change was related to fixing another issue, with 'recurse'.
+ Testing recurse (where not just / is mounted as an overlayroot) is done
+ above
+ echo overlayroot=tmpfs:recurse=1 | sudo overlayroot-chroot tee
/etc/overlayroot.local.conf
+
+ [Other Info]
+ The full overlayroot/init-bottom/overlayroot can be seen at [1]. The
+ specific change that fixed the issue is in revision 115 at [2].
+
+ Related bugs:
+ * bug 1630274 adjusted the mechanism for determining if overlay was
supported.
+ The change to do so is included in the xenial backport for this bug.
+
+ [1]
http://bazaar.launchpad.net/~cloud-initramfs-tools/cloud-initramfs-tools/trunk/view/head:/overlayroot/scripts/init-bottom/overlayroot
+ [2]
http://bazaar.launchpad.net/~cloud-initramfs-tools/cloud-initramfs-tools/trunk/revision/115
+
+ === End SRU Template ===
+
+
+ === Original Description ===
+ As mentioned in LP: #1411294, it's now called 'overlay' instead of
'overlayfs'.
+ Ubuntu had patched the kernel for compatibility.
+
+ The Ubuntu kernels as of 4.8 (16.10 kernel) and possibly a bit before no
+ longer have a overlayfs module either. Thus, this is now affecting
+ yakkety.
+
+ (The original reporter is @~gpo-9.)
+
The changes recently added to mount-image-callback under bug 1493188
that were targeted at supporting 'overlay' filesystem type while still
supporting 'overlayfs' may result in exiting with "unsupported" when a
mount would work.
The changes basically said:
if overlay in /proc/filesystems:
return GOOD
modprobe --quiet --use-blacklist overlay
if overlay in /proc/filesystems:
return GOOD
return BAD
the path that fails now that previously succeeded is when 'modprobe'
would not work, but 'mount -t overlay' *would*. This occurs in build
systems where the running kernel is of one version and code is running
in a chroot that does not have access to the kernel modules in
/lib/modules/.
'mount -t overlay' works in this scenario because the mount abi call passes
the filesystem type 'overlay', and the kernel then does:
fs/filesystems.c: if (!fs && (request_module("fs-%.*s", len, name)
== 0))
The kernel's scope is not chrooted, so the module gets loaded and
everything is happy.
The new changes are to instead basically do:
- for fstype in overlay overlayfs; do
- mount -t $fstype <options> && return GOOD
- if /proc/filesystems is readable and $fstype in /proc/filesystems; then
- return FAIL
- fi
- done
+ for fstype in overlay overlayfs; do
+ mount -t $fstype <options> && return GOOD
+ if /proc/filesystems is readable and $fstype in /proc/filesystems; then
+ return FAIL
+ fi
+ done
--
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https://bugs.launchpad.net/bugs/1630274
Title:
mount-image-callback may not mount overlay when it could
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