Package: autopkgtest Version: 4.1 Severity: normal Tags: patch btrfs gets *really* confused if you attach multiple copies of the same filesystem, because it tracks filesystems by UUID, not by device node (part of its built-in RAID-equivalent): <https://btrfs.wiki.kernel.org/index.php/Gotchas#Block-level_copies_of_devices>
In my experiments with a btrfs-based virtual machine, /proc/self/mounts etc. thought the mounted partitions and subvolumes all came from /dev/vdb, even though they clearly weren't because only /dev/vda could have been mounted read/write. For least-astonishment, the default should perhaps be to *not* provide the base image as a block device (and tests that need to exercise nested virtualization can specifically ask for it), but that would be a behaviour change so I haven't done it in the attached patch. -- System Information: Debian Release: stretch/sid APT prefers unstable-debug APT policy: (500, 'unstable-debug'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental-debug'), (1, 'experimental') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 4.7.0-1-amd64 (SMP w/4 CPU cores) Locale: LANG=en_GB.utf8, LC_CTYPE=en_GB.utf8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system) Versions of packages autopkgtest depends on: ii apt-utils 1.3.1 ii libdpkg-perl 1.18.10 ii procps 2:3.3.12-2 ii python3 3.5.1-4 ii python3-debian 0.1.29 Versions of packages autopkgtest recommends: ii autodep8 0.8 Versions of packages autopkgtest suggests: pn lxc <none> pn lxd-client <none> ii qemu-system 1:2.7+dfsg-1 ii qemu-utils 1:2.7+dfsg-1 ii schroot 1.6.10-2+b1 -- no debconf information
>From e5bb6c8d765da5622189f322815b9b92b45ad540 Mon Sep 17 00:00:00 2001 From: Simon McVittie <simon.mcvit...@collabora.co.uk> Date: Wed, 26 Oct 2016 18:02:00 +0100 Subject: [PATCH 2/5] autopkgtest-virt-qemu: add --no-attach-base-image option btrfs gets *really* confused if you attach multiple copies of the same filesystem, because it tracks filesystems by UUID, not by device node (part of its built-in RAID-equivalent): <https://btrfs.wiki.kernel.org/index.php/Gotchas#Block-level_copies_of_devices> In my experiments with a btrfs-based virtual machine, /proc/self/mounts etc. thought the mounted partitions and subvolumes all came from /dev/vdb, even though they clearly weren't because only /dev/vda could have been mounted read/write. For least-astonishment, the default should perhaps be to *not* provide the base image as a block device (and tests that need to exercise nested virtualization can specifically ask for it), but that would be a behaviour change so I haven't done it here. Signed-off-by: Simon McVittie <simon.mcvit...@collabora.co.uk> --- virt/autopkgtest-virt-qemu | 9 +++++++++ virt/autopkgtest-virt-qemu.1 | 17 ++++++++++++++++- 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/virt/autopkgtest-virt-qemu b/virt/autopkgtest-virt-qemu index 0036f2e..bfb8e73 100755 --- a/virt/autopkgtest-virt-qemu +++ b/virt/autopkgtest-virt-qemu @@ -89,6 +89,12 @@ def parse_args(): help='Enable debugging output') parser.add_argument('--qemu-options', help='Pass through arguments to QEMU command.') + parser.add_argument('--attach-base-image', action='store_true', + default=True, + help='Attach base image as an extra virtual disk') + parser.add_argument('--no-attach-base-image', action='store_false', + default=True, dest='attach_base_image', + help='Attach base image as an extra virtual disk') parser.add_argument('image', nargs='+', help='disk image to add to the VM (in order)') @@ -192,6 +198,9 @@ def login_tty_and_setup_shell(): def setup_baseimage(): '''setup /dev/baseimage in VM''' + if not args.attach_base_image: + return + term = VirtSubproc.get_unix_socket(os.path.join(workdir, 'ttyS1')) # Setup udev rules for /dev/baseimage; set link_priority to -1024 so diff --git a/virt/autopkgtest-virt-qemu.1 b/virt/autopkgtest-virt-qemu.1 index 39602b4..a62dde9 100644 --- a/virt/autopkgtest-virt-qemu.1 +++ b/virt/autopkgtest-virt-qemu.1 @@ -26,7 +26,7 @@ does the given images, but will instead create a temporary overlay for the primary image, and add all other images as read-only. -The first image without the overlay is always added as an additional +By default, the first image without the overlay is added as an additional read-only hard drive, which will be available for tests as .IR /dev/baseimage . This allows tests that require nested VMs to reuse the same image. Be @@ -35,6 +35,9 @@ aware that will not be accessible between calling .B autopkgtest-reboot-prepare and the next boot, thus make sure to stop accessing it before. +The +.B \-\-no\-attach\-base\-image +command-line option disables this behaviour. .SH REQUIREMENTS .B autopkgtest-virt-qemu @@ -108,6 +111,18 @@ Show boot messages from serial console. Enable debugging output. .TP +.BR \-\-attach\-base\-image ", " \-\-no\-attach\-base\-image +Enable or disable attaching a read-only copy of the base image (without the +read/write overlay) for the first disk image as an extra virtual disk, with +hardware serial number +.B BASEIMAGE +and udev rules to create a symbolic link +.BR /dev/baseimage . +This allows tests that require nested VMs to reuse the same image, but is +a very bad idea when using btrfs, which is confused by the duplicate +filesystem UUIDs. + +.TP .BI "--qemu-options=" arguments Pass through arguments to QEMU command; e. g. --qemu-options='-readconfig qemu.cfg' -- 2.10.1
