tools/bootconfig: render kernel.* subtree as cmdline string with -C

Add a -C option that finds the "kernel" subtree of a bootconfig file
and prints it as a flat, space-separated cmdline string by calling the
shared xbc_snprint_cmdline() renderer. An empty or absent kernel.*
subtree produces empty output and exits successfully.

This lets the kernel build embed a bootconfig file as a plain cmdline
string at build time, so embedded bootconfig values can reach
parse_early_param() during architecture setup without parsing the
bootconfig at runtime.

The renderer is intentionally limited to the kernel.* subtree: that is
the only thing the kernel build needs to embed; init.* and other
subtrees keep going through the runtime parser.

Example of this new mode:
	# cat /tmp/test.bconf
	kernel {
		foo = bar
		baz = "hello world"
		arr = 1, 2
	}
	init.foo = nope

	# ./tools/bootconfig/bootconfig -C /tmp/test.bconf
	foo=bar baz="hello world" arr=1 arr=2 %

Link: https://lore.kernel.org/all/20260508-bootconfig_using_tools-v1-2-1132219aa773@debian.org/
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

diff --git a/tools/bootconfig/main.c b/tools/bootconfig/main.c
index 643f707b8f1da1838fb828f8478c7db4800cc855..e1bfab044fbcb6498ae66d04f5e4692168e6f4f5 100644 (file)
--- a/tools/bootconfig/main.c
+++ b/tools/bootconfig/main.c
@@ -286,7 +286,41 @@ static int init_xbc_with_error(char *buf, int len)
        return ret;
 }
 
-static int show_xbc(const char *path, bool list)
+static int show_xbc_kernel_cmdline(void)
+{
+       struct xbc_node *root;
+       char *buf = NULL;
+       int len, ret;
+
+       root = xbc_find_node("kernel");
+       if (!root)
+               return 0;       /* no kernel.* keys: emit empty output */
+
+       len = xbc_snprint_cmdline(NULL, 0, root);
+       if (len < 0) {
+               pr_err("Failed to size cmdline output: %d\n", len);
+               return len;
+       }
+       if (len == 0)
+               return 0;
+
+       buf = malloc(len + 1);
+       if (!buf)
+               return -ENOMEM;
+
+       ret = xbc_snprint_cmdline(buf, len + 1, root);
+       if (ret < 0) {
+               pr_err("Failed to render cmdline output: %d\n", ret);
+               free(buf);
+               return ret;
+       }
+
+       fputs(buf, stdout);
+       free(buf);
+       return 0;
+}
+
+static int show_xbc(const char *path, bool list, bool render_cmdline)
 {
        int ret, fd;
        char *buf = NULL;
@@ -322,11 +356,14 @@ static int show_xbc(const char *path, bool list)
                if (init_xbc_with_error(buf, ret) < 0)
                        goto out;
        }
-       if (list)
+       if (render_cmdline)
+               ret = show_xbc_kernel_cmdline();
+       else if (list)
                xbc_show_list();
        else
                xbc_show_compact_tree();
-       ret = 0;
+       if (ret > 0)
+               ret = 0;
 out:
        free(buf);
 
@@ -486,7 +523,10 @@ static int usage(void)
                " Options:\n"
                "               -a <config>: Apply boot config to initrd\n"
                "               -d : Delete boot config file from initrd\n"
-               "               -l : list boot config in initrd or file\n\n"
+               "               -l : list boot config in initrd or file\n"
+               "               -C : render the kernel.* subtree as a flat cmdline\n"
+               "                    string (suitable for embedding in a kernel image)\n"
+               "                    and print it to stdout\n\n"
                " If no option is given, show the bootconfig in the given file.\n");
        return -1;
 }
@@ -495,10 +535,11 @@ int main(int argc, char **argv)
 {
        char *path = NULL;
        char *apply = NULL;
+       bool render_cmdline = false;
        bool delete = false, list = false;
        int opt;
 
-       while ((opt = getopt(argc, argv, "hda:l")) != -1) {
+       while ((opt = getopt(argc, argv, "hda:lC")) != -1) {
                switch (opt) {
                case 'd':
                        delete = true;
@@ -509,14 +550,17 @@ int main(int argc, char **argv)
                case 'l':
                        list = true;
                        break;
+               case 'C':
+                       render_cmdline = true;
+                       break;
                case 'h':
                default:
                        return usage();
                }
        }
 
-       if ((apply && delete) || (delete && list) || (apply && list)) {
-               pr_err("Error: You can give one of -a, -d or -l at once.\n");
+       if ((!!apply + !!delete + !!list + !!render_cmdline) > 1) {
+               pr_err("Error: You can give one of -a, -d, -l or -C at once.\n");
                return usage();
        }
 
@@ -532,5 +576,5 @@ int main(int argc, char **argv)
        else if (delete)
                return delete_xbc(path);
 
-       return show_xbc(path, list);
+       return show_xbc(path, list, render_cmdline);
 }