lxc-copy fails on btrfs-backed container

[jonjonw]

Issue description

I am unable to clone a btrfs-backed container. It appears to be using the wrong path for the base rootfs.

Steps to reproduce

1. On a btrfs volume, create a container:
   lxc-create -n base -B btrfs -t download -- --dist archlinux --release current --arch amd64
2. Attempt to make a copy of the container: lxc-clone -n base -N child -B btrfs
3. Confirm it was not created: lxc-ls

Information to attach

Adding -o to get some logs gives:
# lxc-copy -n base -N child -B btrfs -o /var/log/lxc/child.log
lxc-copy: base: storage/btrfs.c: btrfs_create_snapshot: 530 Invalid cross-device link - Failed to create btrfs snapshot "/var/lib/lxc/child/rootfs" from "/usr/lib/lxc/rootfs"
lxc-copy: base: lxccontainer.c: copy_storage: 3571 Error copying storage.
lxc-copy: base: tools/lxc_copy.c: do_clone: 369 Failed to clone

Note the error indicates "from "/usr/lib/lxc/rootfs"" but the rootfs for base is at "/var/lib/lxc/base/rootfs"

Required information

• Distribution: archlinux
• The output of
  • lxc-start --version: 3.0.2
  • lxc-checkconfig
    `--- Namespaces ---
    Namespaces: enabled
    Utsname namespace: enabled
    Ipc namespace: enabled
    Pid namespace: enabled
    User namespace: enabled
    Network namespace: enabled

--- Control groups ---
Cgroups: enabled

Cgroup v1 mount points:
/sys/fs/cgroup/systemd
/sys/fs/cgroup/cpu
/sys/fs/cgroup/freezer
/sys/fs/cgroup/cpuset
/sys/fs/cgroup/memory
/sys/fs/cgroup/pids
/sys/fs/cgroup/devices
/sys/fs/cgroup/perf_event
/sys/fs/cgroup/hugetlb
/sys/fs/cgroup/net_cls,net_prio
/sys/fs/cgroup/blkio
/sys/fs/cgroup/rdma

Cgroup v2 mount points:
/sys/fs/cgroup/unified

Cgroup v1 clone_children flag: enabled
Cgroup device: enabled
Cgroup sched: enabled
Cgroup cpu account: missing
Cgroup memory controller: enabled
Cgroup cpuset: enabled

--- Misc ---
Veth pair device: enabled, not loaded
Macvlan: enabled, loaded
Vlan: enabled, not loaded
Bridges: enabled, loaded
Advanced netfilter: enabled, not loaded
CONFIG_NF_NAT_IPV4: enabled, not loaded
CONFIG_NF_NAT_IPV6: enabled, not loaded
CONFIG_IP_NF_TARGET_MASQUERADE: enabled, not loaded
CONFIG_IP6_NF_TARGET_MASQUERADE: enabled, not loaded
CONFIG_NETFILTER_XT_TARGET_CHECKSUM: enabled, not loaded
CONFIG_NETFILTER_XT_MATCH_COMMENT: enabled, not loaded
FUSE (for use with lxcfs): enabled, loaded

--- Checkpoint/Restore ---
checkpoint restore: enabled
CONFIG_FHANDLE: enabled
CONFIG_EVENTFD: enabled
CONFIG_EPOLL: enabled
CONFIG_UNIX_DIAG: enabled
CONFIG_INET_DIAG: enabled
CONFIG_PACKET_DIAG: enabled
CONFIG_NETLINK_DIAG: enabled
File capabilities:

Note : Before booting a new kernel, you can check its configuration
usage : CONFIG=/path/to/config /usr/bin/lxc-checkconfig
`

• uname -a
Linux ghost 4.18.9-1-ck-skylake #1 SMP PREEMPT Wed Sep 19 21:04:45 EDT 2018 x86_64 GNU/Linux
• cat /proc/self/cgroup
12:rdma:/ 11:blkio:/ 10:net_cls,net_prio:/ 9:hugetlb:/ 8:perf_event:/ 7:devices:/user.slice 6:pids:/user.slice/user-1000.slice/user@1000.service 5:memory:/user.slice/user-1000.slice/user@1000.service 4:cpuset:/ 3:freezer:/ 2:cpu:/ 1:name=systemd:/user.slice/user-1000.slice/user@1000.service/gnome-terminal-server.service 0::/user.slice/user-1000.slice/user@1000.service/gnome-terminal-server.service
• cat /proc/1/mounts
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0 sys /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0 dev /dev devtmpfs rw,nosuid,relatime,size=16278644k,nr_inodes=4069661,mode=755 0 0 run /run tmpfs rw,nosuid,nodev,relatime,mode=755 0 0 efivarfs /sys/firmware/efi/efivars efivarfs rw,nosuid,nodev,noexec,relatime 0 0 /dev/nvme0n1p2 / ext4 rw,noatime 0 0 securityfs /sys/kernel/security securityfs rw,nosuid,nodev,noexec,relatime 0 0 tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0 devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0 tmpfs /sys/fs/cgroup tmpfs ro,nosuid,nodev,noexec,mode=755 0 0 cgroup2 /sys/fs/cgroup/unified cgroup2 rw,nosuid,nodev,noexec,relatime,nsdelegate 0 0 cgroup /sys/fs/cgroup/systemd cgroup rw,nosuid,nodev,noexec,relatime,xattr,name=systemd 0 0 pstore /sys/fs/pstore pstore rw,nosuid,nodev,noexec,relatime 0 0 bpf /sys/fs/bpf bpf rw,nosuid,nodev,noexec,relatime,mode=700 0 0 cgroup /sys/fs/cgroup/cpu cgroup rw,nosuid,nodev,noexec,relatime,cpu 0 0 cgroup /sys/fs/cgroup/freezer cgroup rw,nosuid,nodev,noexec,relatime,freezer 0 0 cgroup /sys/fs/cgroup/cpuset cgroup rw,nosuid,nodev,noexec,relatime,cpuset 0 0 cgroup /sys/fs/cgroup/memory cgroup rw,nosuid,nodev,noexec,relatime,memory 0 0 cgroup /sys/fs/cgroup/pids cgroup rw,nosuid,nodev,noexec,relatime,pids 0 0 cgroup /sys/fs/cgroup/devices cgroup rw,nosuid,nodev,noexec,relatime,devices 0 0 cgroup /sys/fs/cgroup/perf_event cgroup rw,nosuid,nodev,noexec,relatime,perf_event 0 0 cgroup /sys/fs/cgroup/hugetlb cgroup rw,nosuid,nodev,noexec,relatime,hugetlb 0 0 cgroup /sys/fs/cgroup/net_cls,net_prio cgroup rw,nosuid,nodev,noexec,relatime,net_cls,net_prio 0 0 cgroup /sys/fs/cgroup/blkio cgroup rw,nosuid,nodev,noexec,relatime,blkio 0 0 cgroup /sys/fs/cgroup/rdma cgroup rw,nosuid,nodev,noexec,relatime,rdma 0 0 systemd-1 /proc/sys/fs/binfmt_misc autofs rw,relatime,fd=36,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=9761 0 0 debugfs /sys/kernel/debug debugfs rw,relatime 0 0 mqueue /dev/mqueue mqueue rw,relatime 0 0 hugetlbfs /dev/hugepages hugetlbfs rw,relatime,pagesize=2M 0 0 binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc rw,relatime 0 0 configfs /sys/kernel/config configfs rw,relatime 0 0 /dev/sda2 /var/lib/lxc btrfs rw,noatime,compress=zstd,space_cache,autodefrag,subvolid=24190,subvol=/lxc 0 0 /dev/sda2 /mnt/btrfs/tank btrfs rw,noatime,compress=zstd,space_cache,autodefrag,subvolid=5,subvol=/ 0 0