Re: [RFC PATCH 2/2] tracing: Record and show boot ID in last_boot_info

[Google]

On Thu, 21 May 2026 11:16:30 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Thu, 21 May 2026 23:57:16 +0900
> "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:
> 
> > @@ -4804,6 +4806,7 @@ struct trace_mod_entry {
> >  struct trace_scratch {
> >  	unsigned int		clock_id;
> >  	unsigned long		text_addr;
> > +	u8			boot_id[UUID_SIZE];
> >  	unsigned long		nr_entries;
> >  	struct trace_mod_entry	entries[];
> >  };
> 
> I just don't like wasting scratch space if boot_id isn't defined. But I
> can't figure out a way to optionally have it there without wasting space
> anyway.

Yeah, it needs to be placed in the scratch area or ring-buffer meta page.
In most cases the boot_id is enabled (random subsystem seems to provide
this UUID always), so it will be rarely waste of memory except
CONFIG_SYSCTL=n.

> 
> If the get_boot_id() is accepted by the random folks, then I'm fine with
> this change.

Yeah, BTW, Sashiko found this can be initialized before we get enough
entropy for random seed. Maybe we need one more delay.

Thank you,


> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>