Re: [PATCH 2/4] tracing/user_events: Introduce multi-format events

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Mon, 29 Jan 2024 09:29:07 -0800
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> On Fri, Jan 26, 2024 at 03:04:45PM -0500, Steven Rostedt wrote:
> > On Fri, 26 Jan 2024 11:10:07 -0800
> > Beau Belgrave <beaub@linux.microsoft.com> wrote:
> > 
> > > > OK, so the each different event has suffixed name. But this will
> > > > introduce non C-variable name.
> > > > 
> > > > Steve, do you think your library can handle these symbols? It will
> > > > be something like "event:[1]" as the event name.
> > > > Personally I like "event.1" style. (of course we need to ensure the
> > > > user given event name is NOT including such suffix numbers)
> > > >   
> > > 
> > > Just to clarify around events including a suffix number. This is why
> > > multi-events use "user_events_multi" system name and the single-events
> > > using just "user_events".
> > > 
> > > Even if a user program did include a suffix, the suffix would still get
> > > appended. An example is "test" vs "test:[0]" using multi-format would
> > > result in two tracepoints ("test:[0]" and "test:[0]:[1]" respectively
> > > (assuming these are the first multi-events on the system).
> > > 
> > > I'm with you, we really don't want any spoofing or squatting possible.
> > > By using different system names and always appending the suffix I
> > > believe covers this.
> > > 
> > > Looking forward to hearing Steven's thoughts on this as well.
> > 
> > I'm leaning towards Masami's suggestion to use dots, as that won't conflict
> > with special characters from bash, as '[' and ']' do.
> > 
> 
> Thanks, yeah ideally we wouldn't use special characters.
> 
> I'm not picky about this. However, I did want something that clearly
> allowed a glob pattern to find all versions of a given register name of
> user_events by user programs that record. The dot notation will pull in
> more than expected if dotted namespace style names are used.
> 
> An example is "Asserts" and "Asserts.Verbose" from different programs.
> If we tried to find all versions of "Asserts" via glob of "Asserts.*" it
> will pull in "Asserts.Verbose.1" in addition to "Asserts.0".

If we use dot for the suffix number, we can prohibit user to use it
for their name. They still can use '_' (or change the group name?)
I just concerned that the name can be parsed by existing tools. Since
':' is used as a separator for group and event name in some case (e.g.
tracefs "set_event" is using, so trace-cmd and perf is using it.)

> While a glob of "Asserts.[0-9]" works when the unique ID is 0-9, it
> doesn't work if the number is higher, like 128. If we ever decide to
> change the ID from an integer to say hex to save space, these globs
> would break.

Hmm, why can't we use regexp?
And if we limits the number of events up to 1000 for each same-name event
we can use fixed numbers, like Assets.[0-9][0-9][0-9]

Thank you,

> 
> Is there some scheme that fits the C-variable name that addresses the
> above scenarios? Brackets gave me a simple glob that seemed to prevent a
> lot of this ("Asserts.\[*\]" in this case).
> 
> Are we confident that we always want to represent the ID as a base-10
> integer vs a base-16 integer? The suffix will be ABI to ensure recording
> programs can find their events easily.
> 
> Thanks,
> -Beau
> 
> > -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>