[PATCH v4 01/20] cmdline: Add generic function to build command line.

[Christophe Leroy <christophe.leroy@csgroup.eu>]

This code provides architectures with a way to build command line
based on what is built in the kernel and what is handed over by the
bootloader, based on selected compile-time options.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v3:
- Addressed comments from Will
- Added capability to have src == dst
v4:
- Add cmdline_strlcpy()
- Removed cmdline_build() macro, __cmdline_build() becomes cmdline_build()
- Fixed the destination length to COMMAND_LINE_SIZE
- Truncate at a space not in a quote when too long
- Added a message when forcing the command line
---
 include/linux/cmdline.h | 79 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 include/linux/cmdline.h

diff --git a/include/linux/cmdline.h b/include/linux/cmdline.h
new file mode 100644
index 000000000000..a0773dc365c7
--- /dev/null
+++ b/include/linux/cmdline.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_CMDLINE_H
+#define _LINUX_CMDLINE_H
+
+#include <linux/string.h>
+#include <linux/printk.h>
+#include <asm/setup.h>
+
+/* Allow users to override strlcat/strlcpy, powerpc can't use strings so early*/
+#ifndef cmdline_strlcat
+#define cmdline_strlcat strlcat
+#define cmdline_strlcpy strlcpy
+#endif
+
+/*
+ * This function will append or prepend a builtin command line to the command
+ * line provided by the bootloader. Kconfig options can be used to alter
+ * the behavior of this builtin command line.
+ * @dst: The destination of the final command line (Min. size COMMAND_LINE_SIZE)
+ * @src: The starting string or NULL if there isn't one. Must not equal dst.
+ * Returns: false if the string was truncated, true otherwise
+ */
+static __always_inline bool __cmdline_build(char *dst, const char *src)
+{
+	int len;
+	char *ptr, *last_space;
+	bool in_quote = false;
+
+	if (IS_ENABLED(CONFIG_CMDLINE_FORCE))
+		src = NULL;
+
+	dst[0] = 0;
+
+	if (IS_ENABLED(CONFIG_CMDLINE_PREPEND))
+		len = cmdline_strlcat(dst, CONFIG_CMDLINE " ", COMMAND_LINE_SIZE);
+
+	len = cmdline_strlcat(dst, src, COMMAND_LINE_SIZE);
+
+	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
+		len = cmdline_strlcat(dst, " " CONFIG_CMDLINE, COMMAND_LINE_SIZE);
+
+	if (len < COMMAND_LINE_SIZE - 1)
+		return true;
+
+	for (ptr = dst; *ptr; ptr++) {
+		if (*ptr == '"')
+			in_quote = !in_quote;
+		if (*ptr == ' ' && !in_quote)
+			last_space = ptr;
+	}
+	if (last_space)
+		*last_space = 0;
+
+	return false;
+}
+
+/*
+ * This function will append or prepend a builtin command line to the command
+ * line provided by the bootloader. Kconfig options can be used to alter
+ * the behavior of this builtin command line.
+ * @dst: The destination of the final command line (Min. size COMMAND_LINE_SIZE)
+ * @src: The starting string or NULL if there isn't one.
+ */
+static __always_inline void cmdline_build(char *dst, const char *src)
+{
+	static char tmp[COMMAND_LINE_SIZE] __initdata;
+
+	if (src == dst) {
+		cmdline_strlcpy(tmp, src, COMMAND_LINE_SIZE);
+		src = tmp;
+	}
+	if (!__cmdline_build(dst, src))
+		pr_warn("Command line is too long, it has been truncated\n");
+
+	if (IS_ENABLED(CONFIG_CMDLINE_FORCE))
+		pr_info("Forcing kernel command line to: %s\n", dst);
+}
+
+#endif /* _LINUX_CMDLINE_H */
-- 
2.25.0