[PATCH] bootstd: Allow PXE boot to be disabled

[Tony Dinh]

Hi Tom,

On Mon, Oct 13, 2025 at 7:40 AM Tom Rini <trini at konsulko.com> wrote:
>
> On Sun, Oct 12, 2025 at 08:12:59PM -0700, Tony Dinh wrote:
> > Hi Simon,
> >
> > On Sat, Oct 11, 2025 at 11:52 PM Simon Glass <sjg at chromium.org> wrote:
> > >
> > > Hi Tony,
> > >
> > > On Sat, 11 Oct 2025 at 20:41, Tony Dinh <mibodhi at gmail.com> wrote:
> > > >
> > > > On Sat, Oct 11, 2025 at 7:37 AM Tom Rini <trini at konsulko.com> wrote:
> > > > >
> > > > > On Sat, Oct 11, 2025 at 01:03:39PM +0100, Peter Robinson wrote:
> > > > > > On Fri, 10 Oct 2025 at 15:28, Tom Rini <trini at konsulko.com> wrote:
> > > > > > >
> > > > > > > On Thu, Oct 09, 2025 at 10:29:17PM -0700, Tony Dinh wrote:
> > > > > > >
> > > > > > > > Make it possible to disable CMD_PXE.
> > > > > > > > Remove unnecessary PXE_UTILS selection in BOOTMETH_EXTLINUX config.
> > > > > > > > In extlinux_boot(), invoke pxe utils only when
> > > > > > > > CONFIG_BOOTMETH_EXTLINUX_PXE is enabled.
> > > > > > > >
> > > > > > > > This patch results in about 9K reduction in image size when
> > > > > > > > PXE boot is disabled.
> > > > > > > >
> > > > > > > > Signed-off-by: Tony Dinh <mibodhi at gmail.com>
> > > > > > > > ---
> > > > > > > >
> > > > > > > >  boot/Kconfig             |  3 +--
> > > > > > > >  boot/bootmeth_extlinux.c | 18 ++++++++++--------
> > > > > > > >  2 files changed, 11 insertions(+), 10 deletions(-)
> > > > > > >
> > > > > > > Is some part of the symbol logic here wrong? A challenge is that "PXE"
> > > > > > > is also where the logic to parse extlinux.conf style files came from,
> > > > > > > and I thought we had split those two out. And then there's this:
> > > > > > >
> > > > > > > >
> > > > > > > > diff --git a/boot/Kconfig b/boot/Kconfig
> > > > > > > > index 2993cd7f9ba..403ce4c3d46 100644
> > > > > > > > --- a/boot/Kconfig
> > > > > > > > +++ b/boot/Kconfig
> > > > > > > > @@ -421,10 +421,10 @@ config BOOT_DEFAULTS_CMDS
> > > > > > > >       select CMD_PART if PARTITIONS
> > > > > > > >       select CMD_DHCP if CMD_NET
> > > > > > > >       select CMD_PING if CMD_NET
> > > > > > > > -     select CMD_PXE if CMD_NET
> > > > > > > >       select CMD_BOOTI if ARM64
> > > > > > > >       select CMD_BOOTZ if ARM && !ARM64
> > > > > > > >       imply CMD_MII if NET
> > > > > > > > +     imply CMD_PXE if CMD_NET
> > >
> > > If you only want scripts, then perhaps you can enable just what you
> > > need, e.g. BOOTMETH_SCRIPT? You may need to disable BOOT_DEFAULTS and
> > > choose your own options.
> >
> > Indeed, that was a missing config when I tried with BOOTSTD_FULL
> > disabled. But there is more, please see below.
> >
> > >
> > > > > > >
> > > > > > > This is one of the things where defaults isn't supposed to be so easy to
> > > > > > > get out of. How many platforms are you wanting to then disable CMD_PXE
> > > > > > > on to save space?
> > > > > >
> > > > > > PXE is generally being removed in a lot of cases as it's not
> > > > > > considered secure and now we have HTTP Boot there are other means of
> > > > > > doing network booting so I think we'll see more and more situations
> > > > > > where we want to disable PXE.
> > > > > >
> > > > > > This is actually something I've been meaning to look at so it's
> > > > > > something I would love to see :)
> > > >
> > > > Glad to hear :)
> > > >
> > > > >
> > > > > And in the world where we also can't just remove ATAGS support because
> > > > > distros (Debian at least) still boots some modern platforms via ATAGS +
> > > > > appended device tree, the high level options for "boot this anywhere"
> > > > > need to perhaps be different from "very modern requirements only
> > > > > distro". I'm not objecting to be clear.
> > > >
> > > > As Tom suggested previously, perhaps looking from a different angle.
> > > > We can disable BOOTSTD_FULL and then try adding only options that are
> > > > needed for a board. Unfortunately this approach did not work when I
> > > > tried it in the past. It seems for bootstd to work well, we need to
> > > > take the whole thing by enabling BOOTSTD_FULL.
> > >
> > > If you end up trying it again, please give a few details here as we
> > > might be able to improve this. When bootstd was first introduced we
> > > had very tight code-size constraints, so quite a few features are only
> > > provided if BOOTSTD_FULL is enabled. Tom has suggested enabling more
> > > features in the base implementation but we haven't really figured out
> > > which.
> >
> > The problem is when a board already has enabled BOOTSTD_FULL or has
> > been updated with Distro Boot (CONFIG_DISTRO_DEFAULTS), all the
> > necessary configurations such as ext2, ext4, efi partition,... are
> > implied, therefore were removed from board defconfig. They must be
> > added back.
> >
> > I actually tried this just now and it does work booting a script from
> > USB drive with this combination:
> >
> > CONFIG_BOOTMETH_SCRIPT=y
> > CONFIG_DISTRO_DEFAULTS=y    (this also selects CMD_PXE, but it's OK
> > for this test)
> > # CONFIG_BOOTSTD_FULL is not set
> >
> > I think it's quite cumbersome to add each of the necessary configs
> > back to the board defconfig. Not as easy as removing CMD_PXE, or other
> > CMD_x to remove a capability.
>
> There's two parts to this. In turns of changing the defconfig to start
> with, you shouldn't need to "add back", if you do:
> $ make foo_defconfig
> $ make menuconfig # Disable full, etc
> $ make savedefconfig
> $ cp defconfig configs/foo_defconfig

Of course you're right! "make menuconfig" works as described above.

Thanks,
Tony

>
> But the second part is that yes, it's at least currently intentional to
> be cumbersome to break the "all stock distributions work in all expected
> use cases" option. If you have networking, networking works in U-Boot,
> but you're not allowing users to install distros over the network like
> they should be able to expect to, it shouldn't be easy.
>
> I am open to splitting the current option up in to multiple parts, along
> the lines of legacy options, modern options, disk options, network
> options since as Peter noted earlier in this thread, PXE is going away
> in favour of HTTP(s) boot. But we still have lots of legacy boards and
> distros to support.
>
> --
> Tom