tools: bpftool: add "bpftool map freeze" subcommand

Add a new subcommand to freeze maps from user space.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/Documentation/bpftool-map.rst

@@ -36,6 +36,7 @@ MAP COMMANDS
 |	**bpftool** **map pop**        *MAP*
 |	**bpftool** **map enqueue**    *MAP* **value** *VALUE*
 |	**bpftool** **map dequeue**    *MAP*
+|	**bpftool** **map freeze**     *MAP*
 |	**bpftool** **map help**
 |
 |	*MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
@@ -127,6 +128,14 @@ DESCRIPTION
 	**bpftool map dequeue**  *MAP*
 		  Dequeue and print **value** from the queue.
 
+	**bpftool map freeze**  *MAP*
+		  Freeze the map as read-only from user space. Entries from a
+		  frozen map can not longer be updated or deleted with the
+		  **bpf\ ()** system call. This operation is not reversible,
+		  and the map remains immutable from user space until its
+		  destruction. However, read and write permissions for BPF
+		  programs to the map remain unchanged.
+
 	**bpftool map help**
 		  Print short help message.
 

tools/bpf/bpftool/bash-completion/bpftool

@@ -449,7 +449,7 @@ _bpftool()
         map)
             local MAP_TYPE='id pinned'
             case $command in
-                show|list|dump|peek|pop|dequeue)
+                show|list|dump|peek|pop|dequeue|freeze)
                     case $prev in
                         $command)
                             COMPREPLY=( $( compgen -W "$MAP_TYPE" -- "$cur" ) )
@@ -638,7 +638,7 @@ _bpftool()
                     [[ $prev == $object ]] && \
                         COMPREPLY=( $( compgen -W 'delete dump getnext help \
                             lookup pin event_pipe show list update create \
-                            peek push enqueue pop dequeue' -- \
+                            peek push enqueue pop dequeue freeze' -- \
                             "$cur" ) )
                     ;;
             esac

tools/bpf/bpftool/map.c

@@ -1262,6 +1262,35 @@ static int do_pop_dequeue(int argc, char **argv)
 	return err;
 }
 
+static int do_freeze(int argc, char **argv)
+{
+	int err, fd;
+
+	if (!REQ_ARGS(2))
+		return -1;
+
+	fd = map_parse_fd(&argc, &argv);
+	if (fd < 0)
+		return -1;
+
+	if (argc) {
+		close(fd);
+		return BAD_ARG();
+	}
+
+	err = bpf_map_freeze(fd);
+	close(fd);
+	if (err) {
+		p_err("failed to freeze map: %s", strerror(errno));
+		return err;
+	}
+
+	if (json_output)
+		jsonw_null(json_wtr);
+
+	return 0;
+}
+
 static int do_help(int argc, char **argv)
 {
 	if (json_output) {
@@ -1286,6 +1315,7 @@ static int do_help(int argc, char **argv)
 		"       %s %s pop        MAP\n"
 		"       %s %s enqueue    MAP value VALUE\n"
 		"       %s %s dequeue    MAP\n"
+		"       %s %s freeze     MAP\n"
 		"       %s %s help\n"
 		"\n"
 		"       " HELP_SPEC_MAP "\n"
@@ -1304,7 +1334,8 @@ static int do_help(int argc, char **argv)
 		bin_name, argv[-2], bin_name, argv[-2], bin_name, argv[-2],
 		bin_name, argv[-2], bin_name, argv[-2], bin_name, argv[-2],
 		bin_name, argv[-2], bin_name, argv[-2], bin_name, argv[-2],
-		bin_name, argv[-2], bin_name, argv[-2], bin_name, argv[-2]);
+		bin_name, argv[-2], bin_name, argv[-2], bin_name, argv[-2],
+		bin_name, argv[-2]);
 
 	return 0;
 }
@@ -1326,6 +1357,7 @@ static const struct cmd cmds[] = {
 	{ "enqueue",	do_update },
 	{ "pop",	do_pop_dequeue },
 	{ "dequeue",	do_pop_dequeue },
+	{ "freeze",	do_freeze },
 	{ 0 }
 };