freebsd-update: refuse to operate on a pkgbase system

FreeBSD-update is not compatible with packaged base.

PR:		282252
Reviewed by:	bapt, markj (earlier)
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D47341

(cherry picked from commit cf1aba2857c1ec59c9a34d363cb18a61ffa34a10)

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
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D47378

(cherry picked from commit 856e158dc4aa5e43f0f15fcd3089fc0d71861b0e)

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

@@ -1046,6 +1046,26 @@ IDS_check_params () {
 	fetch_setup_verboselevel
 }
 
+# Packaged base and freebsd-update are incompatible.  Exit with an error if
+# packaged base is in use.
+check_pkgbase()
+{
+	# Packaged base requires that pkg is bootstrapped.
+	if ! pkg -c ${BASEDIR} -N >/dev/null 2>/dev/null; then
+		return
+	fi
+	# uname(1) is used by pkg to determine ABI, so it should exist.
+	# 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
+https://wiki.freebsd.org/PkgBase for more information.
+EOF
+	exit 1
+}
+
 #### Core functionality -- the actual work gets done here
 
 # Use an SRV query to pick a server.  If the SRV query doesn't provide
@@ -3541,6 +3561,9 @@ 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}