Re: [PATCH v3 1/2] Add support for extlinux.conf

[Alexander Shiyan <eagle.alexander923@gmail.com>]

Hello Sascha.

This change is possible, but then the question arises of how to specify
the default boot entry.
I'd probably prefer to simply specify in the description that we only use
the DEFAULT entry.

Thanks!

чт, 4 июн. 2026 г. в 09:25, Sascha Hauer <s.hauer@pengutronix.de>:
>
> 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@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 <eagle.alexander923@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@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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