LXD stop hook wrapper (#564)

This requires support in `lxd-user` to add support for the `callhook`
subcommand.

Related to canonical/lxd#13331

Depends on canonical/lxd#14253

snapcraft.yaml

@@ -1401,7 +1401,12 @@ parts:
 
       # Build the binaries
       go build -trimpath -o "${CRAFT_PART_INSTALL}/bin/lxc" github.com/canonical/lxd/lxc
-      go build -trimpath -o "${CRAFT_PART_INSTALL}/bin/lxd" -tags=libsqlite3 github.com/canonical/lxd/lxd
+
+      # Build LXD server binary into ${CRAFT_PART_INSTALL}/sbin/lxd so that it does not conflict with the
+      # lxd-stophook wrapper script which is stored in ${CRAFT_PART_INSTALL}/bin/lxd.
+      # This way when a container stops it will call "/snap/lxd/current/bin/lxd callhook" which is handled by the
+      # lxd-stophook script, which in turn will execute "/snap/lxd/current/bin/lxd-user callhook" to notify LXD.
+      go build -trimpath -o "${CRAFT_PART_INSTALL}/sbin/lxd" -tags=libsqlite3 github.com/canonical/lxd/lxd
 
       # Build static binaries
       CGO_ENABLED=0 go build -trimpath -o "${CRAFT_PART_INSTALL}/bin/lxd-agent" -tags=agent,netgo github.com/canonical/lxd/lxd-agent
@@ -1440,7 +1445,7 @@ parts:
       usr/share/misc/: share/misc/
       var/lib/usbutils/usb.ids: share/misc/
       usr/sbin/: bin/
-      sbin/: bin/
+      sbin/sgdisk: bin/
     prime:
       - bin/dnsmasq
       - bin/getfattr
@@ -1461,9 +1466,9 @@ parts:
       - share/misc/usb.ids
 
       - bin/lxc
-      - bin/lxd
       - bin/lxd-agent
       - bin/lxd-user
+      - sbin/lxd
 
   lxd-ui:
     source: https://github.com/canonical/lxd-ui
@@ -1546,10 +1551,12 @@ parts:
       rm -rf "${CRAFT_PRIME}/usr/share/"
 
       # Strip binaries (excluding shell scripts and LXCFS)
+      # The "${CRAFT_PRIME}/bin/lxd" file is ignored as that is the lxd-stophook wrapper script.
       find "${CRAFT_PRIME}"/bin -type f \
         -not -path "${CRAFT_PRIME}/bin/ceph" \
         -not -path "${CRAFT_PRIME}/bin/editor" \
         -not -path "${CRAFT_PRIME}/bin/lxc-checkconfig" \
+        -not -path "${CRAFT_PRIME}/bin/lxd" \
         -not -path "${CRAFT_PRIME}/bin/nvidia-container-cli" \
         -not -path "${CRAFT_PRIME}/bin/remote-viewer" \
         -not -path "${CRAFT_PRIME}/bin/snap-query" \
@@ -1559,7 +1566,10 @@ parts:
         -not -path "${CRAFT_PRIME}/bin/uefivars.py" \
         -not -path "${CRAFT_PRIME}/bin/lxcfs" \
         -not -path "${CRAFT_PRIME}/bin/gpu-2404-custom-wrapper" \
-        -exec strip -s {} +
+        -exec strip --strip-all {} +
+
+      # This is the actual LXD binary.
+      strip --strip-all "${CRAFT_PRIME}/sbin/lxd"
 
       # Strip binaries not under bin/ due to being dynamically
       # added to the path with `snap set lxd`, like `criu.enable=true`
@@ -1602,6 +1612,7 @@ parts:
     organize:
       commands/snap-query: bin/
       hooks/: snap/hooks/
+      wrappers/lxd-stophook: bin/lxd
       wrappers/gpu-2404-custom-wrapper: bin/
       wrappers/editor: bin/
       wrappers/remote-viewer: bin/

snapcraft/wrappers/lxd-stophook

@@ -0,0 +1,8 @@
+#!/bin/sh
+# Use exec so that this script process is replaced.
+# This avoids polluting the process tree with this wrapper script.
+if [ "$1" = "callhook" ]; then
+    exec /snap/lxd/current/bin/lxd-user "$@"
+fi
+
+exec lxd "$@"