Bootconfig updates for v7.2

- bootconfig: Render kernel subtree as cmdline string at build time
   . bootconfig: move xbc_snprint_cmdline() to lib/bootconfig.c. Move the
     xbc_snprint_cmdline() function and its buffer from main.c to the shared
     lib/bootconfig.c parser library so it can be reused by userspace tools.
   . tools/bootconfig: render kernel.* subtree as cmdline string with -C. Add a
     new -C option to print the kernel.* subtree as a flat command-line string
     at build time, allowing early parameter injection without runtime parsing.
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Merge tag 'bootconfig-v7.2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull bootconfig updates from Masami Hiramatsu:

 - bootconfig: move xbc_snprint_cmdline() to lib/bootconfig.c

   Move the xbc_snprint_cmdline() function and its buffer from
   main.c to the shared lib/bootconfig.c parser library so it
   can be reused by userspace tools.

 - render kernel.* subtree as cmdline string with -C

   Add a new -C option to print the kernel.* subtree as a flat
   command-line string at build time, allowing early parameter
   injection without runtime parsing.

* tag 'bootconfig-v7.2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tools/bootconfig: render kernel.* subtree as cmdline string with -C
  bootconfig: move xbc_snprint_cmdline() to lib/bootconfig.c

include/linux/bootconfig.h

@@ -265,6 +265,9 @@ static inline struct xbc_node * __init xbc_node_get_subkey(struct xbc_node *node
 int __init xbc_node_compose_key_after(struct xbc_node *root,
 			struct xbc_node *node, char *buf, size_t size);
 
+/* Render key/value pairs under @root as a flat cmdline string */
+int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root);
+
 /**
  * xbc_node_compose_key() - Compose full key string of the XBC node
  * @node: An XBC node.

init/main.c

@@ -324,51 +324,6 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 
 #ifdef CONFIG_BOOT_CONFIG
 
-static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
-
-#define rest(dst, end) ((end) > (dst) ? (end) - (dst) : 0)
-
-static int __init xbc_snprint_cmdline(char *buf, size_t size,
-				      struct xbc_node *root)
-{
-	struct xbc_node *knode, *vnode;
-	char *end = buf + size;
-	const char *val, *q;
-	int ret;
-
-	xbc_node_for_each_key_value(root, knode, val) {
-		ret = xbc_node_compose_key_after(root, knode,
-					xbc_namebuf, XBC_KEYLEN_MAX);
-		if (ret < 0)
-			return ret;
-
-		vnode = xbc_node_get_child(knode);
-		if (!vnode) {
-			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
-			if (ret < 0)
-				return ret;
-			buf += ret;
-			continue;
-		}
-		xbc_array_for_each_value(vnode, val) {
-			/*
-			 * For prettier and more readable /proc/cmdline, only
-			 * quote the value when necessary, i.e. when it contains
-			 * whitespace.
-			 */
-			q = strpbrk(val, " \t\r\n") ? "\"" : "";
-			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
-				       xbc_namebuf, q, val, q);
-			if (ret < 0)
-				return ret;
-			buf += ret;
-		}
-	}
-
-	return buf - (end - size);
-}
-#undef rest
-
 /* Make an extra command line under given key word */
 static char * __init xbc_make_cmdline(const char *key)
 {

lib/bootconfig.c

@@ -408,6 +408,62 @@ const char * __init xbc_node_find_next_key_value(struct xbc_node *root,
 		return "";	/* No value key */
 }
 
+static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
+
+#define rest(dst, end) ((end) > (dst) ? (end) - (dst) : 0)
+
+/**
+ * xbc_snprint_cmdline() - Render bootconfig keys under @root as a cmdline string
+ * @buf: Destination buffer (may be NULL when @size is 0 to query the length)
+ * @size: Size of @buf in bytes
+ * @root: Subtree root whose key=value pairs should be rendered
+ *
+ * Walk all key/value pairs under @root and emit them as a space-separated
+ * cmdline string into @buf. Values containing whitespace are quoted with
+ * double quotes. Returns the number of bytes that would be written if @buf
+ * were large enough (matching snprintf semantics), or a negative errno on
+ * failure.
+ */
+int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
+{
+	struct xbc_node *knode, *vnode;
+	char *end = buf + size;
+	const char *val, *q;
+	int ret;
+
+	xbc_node_for_each_key_value(root, knode, val) {
+		ret = xbc_node_compose_key_after(root, knode,
+					xbc_namebuf, XBC_KEYLEN_MAX);
+		if (ret < 0)
+			return ret;
+
+		vnode = xbc_node_get_child(knode);
+		if (!vnode) {
+			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
+			if (ret < 0)
+				return ret;
+			buf += ret;
+			continue;
+		}
+		xbc_array_for_each_value(vnode, val) {
+			/*
+			 * For prettier and more readable /proc/cmdline, only
+			 * quote the value when necessary, i.e. when it contains
+			 * whitespace.
+			 */
+			q = strpbrk(val, " \t\r\n") ? "\"" : "";
+			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
+				       xbc_namebuf, q, val, q);
+			if (ret < 0)
+				return ret;
+			buf += ret;
+		}
+	}
+
+	return buf - (end - size);
+}
+#undef rest
+
 /* XBC parse and tree build */
 
 static int __init xbc_init_node(struct xbc_node *node, char *data, uint16_t flag)

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);
 
@@ -488,7 +525,10 @@ 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;
 }
@@ -497,10 +537,11 @@ 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;
@@ -511,14 +552,17 @@ 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();
 	}
 
@@ -534,5 +578,5 @@ 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);
 }