Dynamically lookup the base snap name

[simondeziel]

Rather than hardcode the core base name, look it up where/when needed. This was tested locally:

daemon.start:

$ sudo ls -l /var/snap/lxd/common/mntns/etc/ | grep core
lrwxrwxrwx 1 root root   37 Jan  9 12:48 alternatives -> /snap/core22/current/etc/alternatives
lrwxrwxrwx 1 root root   33 Jan  9 12:48 apparmor -> /snap/core22/current/etc/apparmor
lrwxrwxrwx 1 root root   35 Jan  9 12:48 apparmor.d -> /snap/core22/current/etc/apparmor.d

editor:

$ EDITOR=foo lxc config edit &
$ grep -a 'core[0-9]*' "/proc/$(pgrep vim.tiny)/environ"
LESSOPEN=| /usr/bin/lesspipe %s
HISTTIMEFORMAT=%F %T 
LANGUAGE=en_CA:en
LC_TIME=C.UTF-8
SNAP_COMMON=/var/snap/lxd/common
SNAP_INSTANCE_KEY=USER=sdeziel
XDG_SESSION_TYPE=x11
LXD_CONF=/home/sdeziel/snap/lxd/common/config
LD_LIBRARY_PATH=/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void:/snap/lxd/x1/lib:/snap/lxd/x1/lib/x86_64-linux-gnu
SHLVL=0
SNAP_UID=1000
TEMPDIR=/tmp
HOME=/home/sdeziel/snap/lxd/x1
SNAP_LIBRARY_PATH=/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void
DESKTOP_SESSION=ubuntu
SNAP_USER_DATA=/home/sdeziel/snap/lxd/x1
...
VIMINIT=source /snap/core22/current/etc/vim/vimrc
...
EDITOR=/snap/lxd/x1/bin/editor foo

kmod:

# nsenter -m -t "$(lxc info | awk '/server_pid:/ {print $2}')" sh -x /usr/sbin/lsmod | grep ^+
+ basename /usr/sbin/lsmod
+ NAME=lsmod
+ sed -n /^name:/ s/^name:\s*\(core[0-9]\{2\}\)/\1/p /meta/snap.yaml
+ SNAP_BASE=core22
+ id -u
+ [ 0 != 0 ]
+ [ lsmod = lsmod ]
+ exec /snap/core22/current/bin/kmod list

[simondeziel]

FTR, I asked if snap could get a SNAP_BASE variable to avoid resorting to "parsing" that yaml file ourselves. https://forum.snapcraft.io/t/environment-variables/7983/36?u=sdeziel