# Re: \[RFC PATCH 2/2\] tracing: Record and show boot ID in last\_boot\_info

- From: Masami Hiramatsu (Google) \<mhiramat@kernel.org\>
- Date: 2026-05-24 01:44:43 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/05/17023792
- Thread: https://ratatoskr.run/linux-trace-kernel/2026/05/17015461/t.md

```text
On Thu, 21 May 2026 11:16:30 -0400
Steven Rostedt [ref] wrote:

> On Thu, 21 May 2026 23:57:16 +0900
> "Masami Hiramatsu (Google)" [ref] 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) [ref]
```