[PATCH v4 1/2] Add support for extlinux.conf

This adds support for the extlinux.conf configuration format, commonly
used by Syslinux and many Linux distributions. The configuration file
is typically located at /boot/extlinux/extlinux.conf or
/extlinux/extlinux.conf and defines boot entries with kernel, initrd,
device tree, and command line options.

The implementation integrates with the existing boot entry framework:
- The extlinux scanner discovers entries on mounted filesystems.
- Only the DEFAULT label is turned into a boot entry (multiple
  LABEL sections are ignored after the default is found).
- Bootm is used to load and start the kernel.
---
barebox@Diasom DS-RK3568-SOM-EVB:/ global.bootm.appendroot=true
barebox@Diasom DS-RK3568-SOM-EVB:/ global.boot.default=mmc1.2
barebox@Diasom DS-RK3568-SOM-EVB:/ boot
ext4 ext40: EXT2 rev 1, inode_size 256, descriptor size 64
Booting entry 'extlinux: linux'
extlinux: Booting extlinux label 'linux'
Adding "root=/dev/mmcblk1p3" to Kernel commandline
Loading ARM aarch64 Linux/EFI image '/mnt/mmc1.2/boot/extlinux/../vmlinuz'
commandline: root=/dev/mmcblk1p3 console=ttyS2,1500000n8 ro systemd.unit=setup.target quiet splash systemd.machine_id=181af2816b4c6b0aef77068e0ccc69ad
Loaded kernel to 0x0a400000, devicetree at 0x000000000fb49000

Signed-off-by: Alexander Shiyan <[email protected]>
---
 common/Kconfig    |  20 ++++
 common/Makefile   |   1 +
 common/extlinux.c | 247 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 268 insertions(+)
 create mode 100644 common/extlinux.c

diff --git a/common/Kconfig b/common/Kconfig
index f9985d8aa4..0708855b78 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -773,6 +773,26 @@ config BLSPEC
 	  on a device and it allows the Operating System to install / update
 	  kernels.
 
+config EXTLINUX
+	bool
+	prompt "Support extlinux.conf"
+	depends on FLEXIBLE_BOOTARGS
+	depends on !SHELL_NONE
+	select BOOT
+	select BOOTM
+	select MMCBLKDEV_ROOTARG if MCI
+	help
+	  Enable this to let barebox parse extlinux.conf configuration files,
+	  commonly used by the Syslinux bootloader and many Linux distributions
+	  (e.g., on SD cards or USB drives).
+	  extlinux.conf is typically located at /boot/extlinux/extlinux.conf or
+	  /extlinux/extlinux.conf. It defines boot entries with kernel, initrd,
+	  device tree, and command line options.
+
+	  Note: barebox only uses the entry specified by the DEFAULT keyword.
+	  Additional LABEL sections are ignored. This allows a simple and
+	  portable way to define a single default boot option.
+
 config FLEXIBLE_BOOTARGS
 	bool
 	prompt "flexible Linux bootargs generation"
diff --git a/common/Makefile b/common/Makefile
index 27c5dea168..cd929b2194 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -9,6 +9,7 @@ obj-y				+= clock.o
 pbl-$(CONFIG_PBL_CLOCKSOURCE)	+= clock.o
 obj-y				+= console_common.o
 obj-$(CONFIG_OFDEVICE)		+= deep-probe.o
+obj-$(CONFIG_EXTLINUX)		+= extlinux.o
 obj-y				+= startup.o
 obj-y				+= misc.o
 obj-pbl-y			+= memsize.o
diff --git a/common/extlinux.c b/common/extlinux.c
new file mode 100644
index 0000000000..caa62923da
--- /dev/null
+++ b/common/extlinux.c
@@ -0,0 +1,247 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-FileCopyrightText: Alexander Shiyan <[email protected]> */
+
+#define pr_fmt(fmt)     "extlinux: " fmt
+
+#include <boot.h>
+#include <bootm.h>
+#include <bootscan.h>
+#include <common.h>
+#include <environment.h>
+#include <fs.h>
+#include <globalvar.h>
+#include <libfile.h>
+#include <libgen.h>
+#include <string.h>
+
+struct extlinux_entry {
+	struct bootentry entry;
+	char *rootpath;
+	char *label;
+	char *kernel;
+	char *initrd;
+	char *fdtdir;
+	char *fdt;
+	char *append;
+};
+
+static int extlinux_boot(struct bootentry *entry, int verbose, int dryrun)
+{
+	struct extlinux_entry *e =
+		container_of(entry, struct extlinux_entry, entry);
+	char *kernel_abs, *initrd_abs = NULL, *fdt_abs = NULL;
+	struct bootm_data data = {};
+	int ret;
+
+	bootm_data_init_defaults(&data);
+
+	data.dryrun = max_t(int, dryrun, data.dryrun);
+	data.verbose = max(verbose, data.verbose);
+
+	kernel_abs = basprintf("%s/%s", e->rootpath, e->kernel);
+	data.os_file = kernel_abs;
+
+	if (e->initrd) {
+		initrd_abs = basprintf("%s/%s", e->rootpath, e->initrd);
+		data.initrd_file = initrd_abs;
+	}
+
+	if (e->fdt) {
+		char *fdtdir = e->fdtdir ? : e->rootpath;
+
+		fdt_abs = basprintf("%s/%s", fdtdir, e->fdt);
+		data.oftree_file = fdt_abs;
+	}
+
+	if (e->append)
+		globalvar_add_simple("linux.bootargs.dyn.bootentries",
+				     e->append);
+
+	pr_info("Booting extlinux label '%s'\n", e->label);
+
+	ret = bootm_entry(entry, &data);
+	if (ret)
+		pr_err("bootm failed: %pe\n", ERR_PTR(ret));
+
+	free(kernel_abs);
+	free(initrd_abs);
+	free(fdt_abs);
+
+	return ret;
+}
+
+static void extlinux_entry_free(struct bootentry *entry)
+{
+	struct extlinux_entry *e =
+		container_of(entry, struct extlinux_entry, entry);
+
+	free(e->rootpath);
+	free(e->label);
+	free(e->kernel);
+	free(e->initrd);
+	free(e->fdtdir);
+	free(e->fdt);
+	free(e->append);
+	free(e);
+}
+
+/*
+ * Parse extlinux.conf. Only the entry pointed to by the DEFAULT keyword
+ * is extracted; all other LABEL sections are ignored.
+ */
+static struct extlinux_entry *parse_extlinux_conf(const char *abspath,
+						  const char *rootpath)
+{
+	char *buf, *bufptr, *line, *default_label = NULL;
+	struct extlinux_entry *entry = NULL;
+
+	bufptr = read_file(abspath, NULL);
+	if (!bufptr)
+		return ERR_PTR(-errno);
+
+	buf = bufptr;
+	while ((line = strsep(&buf, "\n\r")) != NULL) {
+		char *key, *val;
+
+		line = skip_spaces(line);
+
+		if (*line == '#' || *line == '\0')
+			continue;
+
+		key = strsep(&line, " \t");
+		val = isempty(line) ? NULL : skip_spaces(line);
+		if (!key || !val)
+			continue;
+
+		if (!default_label) {
+			if (!strcasecmp(key, "DEFAULT"))
+				default_label = xstrdup(val);
+
+			continue;
+		}
+
+		if (!strcasecmp(key, "LABEL")) {
+			if (!strcmp(val, default_label)) {
+				entry = xzalloc(sizeof(*entry));
+				entry->label = xstrdup(val);
+				entry->rootpath = dirname(xstrdup(abspath));
+			} else if (entry) {
+				break;
+			}
+			continue;
+		}
+
+		if (entry) {
+			if (!strcasecmp(key, "KERNEL"))
+				entry->kernel = xstrdup(val);
+			else if (!strcasecmp(key, "INITRD"))
+				entry->initrd = xstrdup(val);
+			else if (!strcasecmp(key, "FDTDIR"))
+				entry->fdtdir = xstrdup(val);
+			else if (!strcasecmp(key, "FDT"))
+				entry->fdt = xstrdup(val);
+			else if (!strcasecmp(key, "APPEND"))
+				entry->append = xstrdup(val);
+			else
+				pr_warn("Unhandled key: %s\n", key);
+		}
+	}
+
+	free(default_label);
+	free(bufptr);
+
+	if (!entry || !entry->kernel) {
+		if (entry)
+			extlinux_entry_free(&entry->entry);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return entry;
+}
+
+static int _extlinux_scan_file(struct bootscanner *scanner,
+			       struct bootentries *bootentries,
+			       const char *configname,
+			       const char *rootpath)
+{
+	struct extlinux_entry *e;
+
+	if (!strends(configname, "extlinux.conf"))
+		return 0;
+
+	e = parse_extlinux_conf(configname, rootpath);
+	if (IS_ERR(e))
+		return PTR_ERR(e);
+
+	e->entry.boot = extlinux_boot;
+	e->entry.release = extlinux_entry_free;
+	e->entry.path = xstrdup_const(configname);
+	e->entry.title = basprintf("extlinux: %s", e->label);
+	e->entry.description = basprintf("extlinux entry \'%s\" on %s",
+					 e->label, rootpath);
+	e->entry.me.type = MENU_ENTRY_NORMAL;
+
+	bootentries_add_entry(bootentries, &e->entry);
+
+	return 1;
+}
+
+static int extlinux_scan_file(struct bootscanner *scanner,
+			      struct bootentries *bootentries,
+			      const char *configname)
+{
+	const char *rootpath = get_mounted_path(configname);
+
+	if (IS_ERR(rootpath))
+		return PTR_ERR(rootpath);
+
+	return _extlinux_scan_file(scanner, bootentries, configname, rootpath);
+}
+
+static int extlinux_scan_directory(struct bootscanner *scanner,
+				   struct bootentries *bootentries,
+				   const char *rootpath)
+{
+	char *path;
+	struct stat s;
+	int ret;
+
+	path = basprintf("%s/boot/extlinux/extlinux.conf", rootpath);
+	ret = stat(path, &s);
+	if (!ret && S_ISREG(s.st_mode))
+		ret = _extlinux_scan_file(scanner, bootentries, path, rootpath);
+	free(path);
+	if (ret > 0)
+		return ret;
+
+	path = basprintf("%s/extlinux/extlinux.conf", rootpath);
+	ret = stat(path, &s);
+	if (!ret && S_ISREG(s.st_mode))
+		ret = _extlinux_scan_file(scanner, bootentries, path, rootpath);
+	free(path);
+
+	return ret;
+}
+
+static struct bootscanner extlinux_scanner = {
+	.name = "extlinux",
+	.scan_file = extlinux_scan_file,
+	.scan_directory = extlinux_scan_directory,
+};
+
+static int extlinux_generate(struct bootentries *bootentries, const char *name)
+{
+	return bootentry_scan_generate(&extlinux_scanner, bootentries, name);
+}
+
+static struct bootentry_provider extlinux_provider = {
+	.name = "extlinux",
+	.generate = extlinux_generate,
+	.priority = -25,
+};
+
+static int extlinux_init(void)
+{
+	return bootentry_register_provider(&extlinux_provider);
+}
+device_initcall(extlinux_init);
-- 
2.52.0