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

Move xbc_snprint_cmdline() from init/main.c to lib/bootconfig.c so the
function (and its xbc_namebuf scratch buffer) becomes part of the shared
parser library. tools/bootconfig already compiles lib/bootconfig.c
directly, which lets a follow-up patch reuse the same renderer in the
userspace tool to convert a bootconfig file into a flat cmdline string
at build time.

No functional change.

Link: https://lore.kernel.org/all/20260508-bootconfig_using_tools-v1-1-1132219aa773@debian.org/

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

3 files changed, 59 insertions, 45 deletions

diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
index 692a5acc2ffc..1c7f3b74ffcf 100644
--- a/include/linux/bootconfig.h
+++ b/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.
diff --git a/init/main.c b/init/main.c
index 96f93bb06c49..e363232b428b 100644
--- a/init/main.c
+++ b/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)
 {
diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index c470b93d5dbc..f445b7703fdd 100644
--- a/lib/bootconfig.c
+++ b/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)