Re: [for-next][PATCH 04/26] bootconfig: Add Extra Boot Config support

[Geert Uytterhoeven]

Hi Hiramatsu-san,

On Thu, Feb 6, 2020 at 3:42 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> On Thu, 6 Feb 2020 12:54:05 +0100
> Borislav Petkov <bp@xxxxxxxxx> wrote:
> > On Tue, Jan 14, 2020 at 04:03:20PM -0500, Steven Rostedt wrote:
> > > diff --git a/init/Kconfig b/init/Kconfig
> > > index a34064a031a5..63450d3bbf12 100644
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -1215,6 +1215,17 @@ source "usr/Kconfig"
> > >
> > >  endif
> > >
> > > +config BOOT_CONFIG
> > > +   bool "Boot config support"
> > > +   select LIBXBC
> > > +   default y
> >
> > Any particular reason this is default y? Why should it be enabled by
> > default on all boxes?
>
> Oh, you are not the first person asked that :)
>
> https://lkml.org/lkml/2019/12/9/563
>
> And yes, I think this is important that will useful for most developers
> and admins. Since the bootconfig already covers kernel and init options,
> this can be a new standard way to pass args to kernel boot.
>
> And as I reported above thread, the memory footpoint of view, most code
> and working memory are released after boot. Also, as Linus's suggested,
> now this feature is enabled only if user gives "bootconfig" on the kernel
> command line. So the side effect is minimized.

With m68k/atari_defconfig, bloat-o-meter says:

    add/remove: 39/0 grow/shrink: 2/0 up/down: 13086/0 (13086)

which is IMHO not that small for a "default y" option that may or may not
be used.

Especially:

        Function                                     old     new   delta
    xbc_nodes                                      -    8192   +8192

Any chance xbc_nodes can be allocated dynamically, and only when needed?

Yes, there are industrial products running Linux on a current ARM SoC
using the builtin 8 or 10 MiB of SRAM (+ XIP for the kernel), so these
definitely want to say CONFIG_BOOT_CONFIG=n.

Thanks!

add/remove: 39/0 grow/shrink: 2/0 up/down: 13086/0 (13086)
Function                                     old     new   delta
xbc_nodes                                      -    8192   +8192
xbc_init                                       -     854    +854
start_kernel                                1020    1580    +560
copy_xbc_key_value_list                        -     362    +362
__xbc_parse_value                              -     324    +324
xbc_snprint_cmdline                            -     294    +294
xbc_node_compose_key_after                     -     266    +266
xbc_namebuf                                    -     256    +256
xbc_add_sibling                                -     254    +254
xbc_node_find_next_leaf                        -     186    +186
xbc_node_find_child                            -     176    +176
__xbc_add_key                                  -     162    +162
proc_boot_config_init                          -     124    +124
xbc_make_cmdline                               -     122    +122
xbc_node_find_value                            -     104    +104
xbc_node_find_next_key_value                   -     102    +102
__xbc_close_brace                              -      92     +92
find_match_node                                -      80     +80
__xbc_parse_keys                               -      78     +78
xbc_node_get_data                              -      64     +64
xbc_parse_key                                  -      60     +60
skip_comment                                   -      48     +48
xbc_destroy_all                                -      42     +42
xbc_node_get_parent                            -      38     +38
xbc_parse_error                                -      36     +36
xbc_node_get_child                             -      34     +34
xbc_node_get_next                              -      32     +32
boot_config_checksum                           -      30     +30
boot_config_proc_show                          -      26     +26
xbc_root_node                                  -      20     +20
kzalloc.constprop                            810     830     +20
xbc_node_index                                 -      14     +14
xbc_node_num                                   -       4      +4
xbc_data_size                                  -       4      +4
xbc_data                                       -       4      +4
saved_boot_config                              -       4      +4
last_parent                                    -       4      +4
extra_init_args                                -       4      +4
extra_command_line                             -       4      +4
__initcall_proc_boot_config_init5              -       4      +4
xbc_debug_dump                                 -       2      +2
Total: Before=3688860, After=3701946, chg +0.35%

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds