Re: [PATCH 7/7] boot: add a minimal bootmeth for the Boot Loader Specification

[Tom Rini <trini@konsulko.com>]

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On Thu, Jun 25, 2026 at 08:57:13PM +0400, Alexey Charkov wrote:
> On Thu, Jun 25, 2026 at 8:24 PM Simon Glass <sjg@chromium.org> wrote:
> >
> > Hi Alexey,
> >
> > On Thu, 25 Jun 2026 at 16:52, Alexey Charkov <alchark@flipper.net> wrote:
> > >
> > > Hi Simon,
> > >
> > > On Thu, Jun 25, 2026 at 7:28 PM Simon Glass <sjg@chromium.org> wrote:
> > > >
> > > > Hi Alexey,
> > > >
> > > > On 2026-06-04T15:31:05, Alexey Charkov <alchark@flipper.net> wrote:
> > > > > boot: add a minimal bootmeth for the Boot Loader Specification
> > > > >
> > > > > Add a bootmeth that finds and boots Boot Loader Specification (BLS)
> > > > > type #1 entry files [1]. On each block-device partition it scans, the
> > > > > bootmeth looks for files matching '<prefix>loader/entries/*.conf'
> > > > > (where <prefix> comes from bootstd_get_prefixes(), typically '/' and
> > > > > '/boot/'), picks the highest-sorting filename, parses it, and exposes
> > > > > it as a bootflow.
> > > > >
> > > > > Implementation reuses the existing pxelinux infrastructure.
> > > > >
> > > > > For now the entry chosen on a partition is purely the lexicographic
> > > > > maximum of *.conf filenames; sort-key / version field handling
> > > > > (spec-mandated tiebreakers) and boot-counting (the '+TRIES_LEFT'
> > > > > filename suffix) are left as TODOs. Likewise, only the top-sorted entry
> > > > > is surfaced because the bootstd framework currently allows one bootflow
> > > > > per (bootmeth, partition); exposing every discovered entry will require
> > > > > a framework extension.
> > > > >
> > > > > Type #2 BLS (drop-in directory of EFI binaries) is out of scope here;
> > > > > [...]
> > > > >
> > > > > boot/Kconfig        |  17 +++
> > > > >  boot/Makefile       |   1 +
> > > > >  boot/bootmeth_bls.c | 333 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > > >  3 files changed, 351 insertions(+)
> > > >
> > > > > diff --git a/boot/Kconfig b/boot/Kconfig
> > > > > @@ -649,6 +649,23 @@ config BOOTMETH_EXTLINUX_PXE
> > > > > +config BOOTMETH_BLS
> > > > > +     bool "Bootdev support for Boot Loader Specification entries"
> > > > > +     select PXE_UTILS
> > > > > +     default y
> > > >
> > > > Wherever the 'default y' discussion lands, this will be enabled on
> > > > sandbox, so the 'bootmeth list' tests in test/boot/bootmeth.c will
> > > > fail since they check the exact list and count. Please can you run the
> > > > sandbox tests and update them as needed?
> > > >
> > > > Since you are adding a new bootmeth you also need a sandbox test that
> > > > exercises it (see the extlinux tests in test/boot/bootflow.c, with a
> > > > fixture disk image) and a documentation page, e.g.
> > > > doc/develop/bootstd/bls.rst with an entry in the index there.
> > >
> > > Will do, thanks!
> > >
> > > > > diff --git a/boot/bootmeth_bls.c b/boot/bootmeth_bls.c
> > > > > @@ -0,0 +1,333 @@
> > > > > +static int bls_getfile(struct pxe_context *ctx, const char *file_path,
> > > > > +                    char *file_addr, enum bootflow_img_t type, ulong *sizep)
> > > >
> > > > This is a verbatim copy of extlinux_getfile() - please can you export
> > > > that, or move it into a shared helper?
> > >
> > > Ack
> > >
> > > > > diff --git a/boot/bootmeth_bls.c b/boot/bootmeth_bls.c
> > > > > @@ -0,0 +1,333 @@
> > > > > +     ret = bootmeth_alloc_file(bflow, SZ_64K, 1, BFI_EXTLINUX_CFG);
> > > >
> > > > The extlinux bootmeth passes ARCH_DMA_MINALIGN here, since the buffer
> > > > is filled by a block-device read which may use DMA on some platforms.
> > > > An alignment of 1 risks cache-line corruption there, so please use
> > > > ARCH_DMA_MINALIGN.
> > >
> > > Ack
> > >
> > > > > diff --git a/boot/bootmeth_bls.c b/boot/bootmeth_bls.c
> > > > > @@ -0,0 +1,333 @@
> > > > > +     bflow->bootmeth_priv = label;
> > > > > +     free(fpath);
> > > >
> > > > This leaks memory: bootflow_free() releases bootmeth_priv with a plain
> > > > free(), so the label's string members (name, menu, kernel, append,
> > > > initrd, etc.) are never freed - for every bootflow discarded after a
> > > > scan, not just on error paths.
> > > >
> > > > Since get_string() copies tokens out of the buffer rather than
> > > > modifying it in place, you could follow the extlinux approach: keep
> > > > only bflow->buf across the scan (already populated by
> > > > bootmeth_alloc_file() and freed by the framework), use a temporary
> > > > label in bls_read_bootflow() just to extract the title, destroy it
> > > > with label_destroy(), and re-parse the buffer in bls_boot(). Then
> > > > bootmeth_priv is not needed at all. What do you think?
> > >
> > > Will address the leak, thanks for pointing it out!
> > >
> > > The bls_priv structure is needed for my follow-up extension which
> > > allows multiple boot entries to be returned by each (bootdev,
> > > bootmeth, partition) tuple, and I wanted to minimize churn between
> > > those two. I haven't sent that follow-up for review yet, as I wanted
> > > to confirm this simpler version is acceptable first.
> >
> > We should implement this using an generic index rather than something
> > bls-specific...please see some commits at:
> >
> > https://concept.deinde.dev/u-boot/u-boot/-/merge_requests/782
> 
> Oh, there's already BLS in your tree :-D
> 
> Would you like to merge that instead? Your version looks much more
> full-fledged. If you happen to have one rebased on master or next I'd
> be happy to test!

Unfortunately Simon's work here is AI-generated and so not particularly
welcome, among other problems right now.

-- 
Tom

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