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

[Borislav Petkov]

On Sat, Feb 08, 2020 at 12:06:48AM +0900, Masami Hiramatsu wrote:
> OK, could you tell me your idea to make it better? I'm waiting for such
> discussion a half of last year :)

Yah, situation sounds familiar. :)

> For your information, here is the background of this bootconfig.
> To build my boot-time tracing, I need a way to pass a flexible and
> structured configuration at boot time.

Can I see an actual example of what you're doing?

> I had tried to reuse devicetree at first, but it was rejected because
> the devicetree is only for describing hardware. So I introduced this
> bootconfig.

Makes sense.

> When I designed the bootconfig, I tried to sort out the requirements.
> That config should be able to pass all setting we can do on tracefs.
> Since ftrace already has a parser for tracefs, we don't need any types
> for each settings. Thus it should be something like sysctl.conf. But the
> sysctl.conf was too simple, it couldn't handle several related keys
> well. So I decided to introduce braces which put together some related
> parameters. And the bootconfig syntax was born.

Ok, here's my boot command line:

[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.5.0-rc7+ root=/dev/nvme0n1p2 ro root=/dev/disk/by-id/nvme-eui.0025385481b2fe2a-part2 resume=/dev/disk/by-id/nvme-eui.0025385481b2fe2a-part1 debug ignore_loglevel log_buf_len=16M no_console_suspend net.ifnames=0 mem_encrypt=off systemd.log_target=null

How do I use the bootconfig thing with it? Or is it not supposed to be
used that way? IOW, how is it supposed to be used so that it needs to be
enabled on every box?

> Okay, I hope it and try to prove it. Anyway, to use boot-time tracing which
> can fully utilize ftrace at boot-time, we have to enable bootconfig.

Ok, this is getting closer. But not everyone is using boottime tracing?

Or is the logic: every user/tool might need to be able to do boottime
tracing at some future point in time and bootconfig is a mandatory part
of that use case?

Thx.

-- 
Regards/Gruss,
    Boris.

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