Re: [PATCH v7 17/25] trace-cmd library: Read strings sections on file load

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 17 Jan 2022 18:11:38 +0200
Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:

> > Hmm, I don't remember in our conversations. Did we say we would have more
> > than one string section? Or allow it to be broken up? How do offsets work
> > in such cases?
> >
> > I was thinking that we could simply mmap the string section, but that won't
> > work if there's more than one.
> >  
> 
> The first implementation was with a single string section at the end
> of the file. But when I tested that design with the trace-cmd
> guest-host tracing, I realized it is impossible to work without major
> changes in the host-guest protocol. The problem is that in the current
> host-guest tracing logic, part of the guest metadata file is written
> in the guest context, part in the host context. Each of these parts
> can put strings in the string section. That will change the way guest
> metadata is written. That's why decided to use multiple string
> sections in the file. On file read the strings from all sections are
> stored into one memory block, and string offset is the offset in that
> block. As these sections are compressed usually, simple mmap will not
> work even in case of single section.

OK, then we'll just keep it as is.

Thanks,

-- Steve