[PATCH v3 1/2] Add support for extlinux.conf
Sascha Hauer
s.hauer at pengutronix.de
Wed Jun 3 23:25:04 PDT 2026
Hi Alexander,
On 2026-05-29 08:13, Alexander Shiyan wrote:
> 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.
> - The default LABEL is turned into a boot entry.
> - Bootm is used to load and start the kernel.
> ---
> barebox at Diasom DS-RK3568-SOM-EVB:/ global.bootm.appendroot=true
> barebox at Diasom DS-RK3568-SOM-EVB:/ global.boot.default=mmc1.2
> barebox at 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 <eagle.alexander923 at gmail.com>
> ---
> common/Kconfig | 19 ++++
> common/Makefile | 1 +
> common/extlinux.c | 243 ++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 263 insertions(+)
> create mode 100644 common/extlinux.c
>
> diff --git a/common/Kconfig b/common/Kconfig
> index 047dd5390b..6f1eabdf8b 100644
> --- a/common/Kconfig
> +++ b/common/Kconfig
> @@ -776,6 +776,25 @@ 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.
> + This option allows barebox to discover and boot operating systems
> + that follow the extlinux configuration format, providing a simple
> + and portable way to manage multiple boot options.
> +
> config FLEXIBLE_BOOTARGS
> bool
> prompt "flexible Linux bootargs generation"
> diff --git a/common/Makefile b/common/Makefile
> index 21b6cecb3b..6b97edc2c3 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..6ad01cc652
> --- /dev/null
> +++ b/common/extlinux.c
> @@ -0,0 +1,243 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/* SPDX-FileCopyrightText: Alexander Shiyan <shc_work at mail.ru> */
> +
> +#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);
> +}
> +
> +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;
> + }
The extlinux format supports multiple entries, but you return here after
the first entry parsed. We should either document that we only support a
single entry or implement multiple entries.
Unless I am overlooking something it should be quite straight forward to
implement multiple entries, just move the call to bootentries_add_entry()
into this loop.
Sascha
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