Restart GNOME logs in to GNOME, not the account's default session (gaming mode after the conversion); the default is put back afterwards

patches/steamify-gdm-relogin.sh

@@ -6,11 +6,36 @@
 # ("A graphical session is already running!"): so the user is ended first,
 # then GDM restarted. That work runs in its own transient unit, because
 # ending the user kills this process too.
+#
+# An optional session id as the argument ("gnome"): that session is logged in
+# for this time only. The session in AccountsService (what the next boot goes
+# to: gaming mode after the SteamOS conversion) is put back once the new
+# session is up.
 if [[ "$1" != --work ]]; then
     [[ -n "${SUDO_USER:-}" ]] || exit 1
-    exec systemd-run --no-block --collect --unit=steamify-gdm-relogin "$0" --work "$SUDO_USER"
+    exec systemd-run --no-block --collect --unit=steamify-gdm-relogin "$0" --work "$SUDO_USER" "${1:-}"
 fi
 USER_NAME="$2"
+SESSION="$3"
+ACCOUNT="/var/lib/AccountsService/users/$USER_NAME"
+
+# Session= and XSession= of the user, as GDM reads them at the next login.
+get_session() { sed -n "s/^$1=//p" "$ACCOUNT" 2>/dev/null | head -1; }
+set_session() {
+    local key
+    touch "$ACCOUNT"
+    grep -q '^\[User\]' "$ACCOUNT" || echo "[User]" >> "$ACCOUNT"
+    for key in Session XSession; do
+        if grep -q "^$key=" "$ACCOUNT"; then sed -i "s|^$key=.*|$key=$1|" "$ACCOUNT"
+        else sed -i "/^\[User\]/a $key=$1" "$ACCOUNT"; fi
+    done
+    systemctl restart accounts-daemon 2>/dev/null || true
+}
+if [[ -n "$SESSION" ]]; then
+    OLD_SESSION="$(get_session Session)"; OLD_XSESSION="$(get_session XSession)"
+    set_session "${SESSION%.desktop}"
+fi
+
 # GDM is stopped first, so its login screen doesn't show while the old user
 # manager shuts down; a new login right away fails ("A graphical session is
 # already running!", or the session dies at once), so wait until it is gone.
@@ -20,3 +45,14 @@ loginctl terminate-user "$USER_NAME"
 USER_RUNTIME="/run/user/$(id -u "$USER_NAME")"
 for _ in $(seq 120); do [[ -d "$USER_RUNTIME" ]] || break; sleep 0.25; done
 systemctl start gdm.service
+
+if [[ -n "$SESSION" ]]; then
+    # The new session has read what it logs in to once its user manager runs; then the next boot's session goes back.
+    for _ in $(seq 120); do [[ -d "$USER_RUNTIME" ]] && break; sleep 0.25; done
+    sleep 8
+    if [[ -n "$OLD_SESSION" ]]; then
+        sed -i "s|^Session=.*|Session=$OLD_SESSION|" "$ACCOUNT"
+        if [[ -n "$OLD_XSESSION" ]]; then sed -i "s|^XSession=.*|XSession=$OLD_XSESSION|" "$ACCOUNT"; fi
+        systemctl restart accounts-daemon 2>/dev/null || true
+    fi
+fi