freebsd-update: improve pkgbase check

The previous version used a case-insensitive match (default for -x).
The presence of packages like freebsd-git-devtools and freebsd-ftpd
would falsely trigger the packaged base check.

Instead, just use `pkg which /usr/bin/uname` as a packaged base
indication.  pkg uses /usr/bin/uname to determine ABI, so we can rely on
it existing.  If it comes from a package then packaged base is in use.

Also, extend the check to all freebsd-update commands.  It is easier to
just disallow all commands, and easier to test.

Reported by: Mark Millard
Reviewed by: manu
Fixes: cf1aba2857 ("freebsd-update: refuse to operate on a pkgbase system")
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D47378

usr.sbin/freebsd-update/freebsd-update.sh

@@ -1107,12 +1107,13 @@ check_pkgbase()
 	if ! pkg -c ${BASEDIR} -N >/dev/null 2>/dev/null; then
 		return
 	fi
-	# Presence of FreeBSD-* package(s) indicates packaged base.
+	# uname(1) is used by pkg to determine ABI, so it should exist.
-	if ! pkg -c ${BASEDIR} info -q -x '^FreeBSD' 2>/dev/null; then
+	# If it comes from a package then this system uses packaged base.
+	if ! pkg -c ${BASEDIR} which /usr/bin/uname >/dev/null; then
 		return
 	fi
 	cat <<EOF
-FreeBSD-update is incompatible with the use of packaged base.  Please see
+freebsd-update is incompatible with the use of packaged base.  Please see
 https://wiki.freebsd.org/PkgBase for more information.
 EOF
 	exit 1
@@ -3536,7 +3537,6 @@ cmd_cron () {
 
 # Fetch files for upgrading to a new release.
 cmd_upgrade () {
-	check_pkgbase
 	finalize_components_config ${COMPONENTS}
 	upgrade_check_params
 	upgrade_check_kmod_ports
@@ -3571,7 +3571,6 @@ cmd_updatesready () {
 
 # Install downloaded updates.
 cmd_install () {
-	check_pkgbase
 	finalize_components_config ${COMPONENTS}
 	install_check_params
 	install_create_be
@@ -3580,7 +3579,6 @@ cmd_install () {
 
 # Rollback most recently installed updates.
 cmd_rollback () {
-	check_pkgbase
 	finalize_components_config ${COMPONENTS}
 	rollback_check_params
 	rollback_run || exit 1
@@ -3617,6 +3615,9 @@ export LC_ALL=C
 # Clear environment variables that may affect operation of tools that we use.
 unset GREP_OPTIONS
 
+# Disallow use with packaged base.
+check_pkgbase
+
 get_params $@
 for COMMAND in ${COMMANDS}; do
 	cmd_${COMMAND}