Re: [FYI][PATCH] tracing/treewide: Remove second parameter of __assign_str()

[Alison Schofield]

On Fri, Feb 23, 2024 at 12:56:34PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
> 
> [
>    This is a treewide change. I will likely re-create this patch again in
>    the second week of the merge window of v6.9 and submit it then. Hoping
>    to keep the conflicts that it will cause to a minimum.
> ]
> 
> With the rework of how the __string() handles dynamic strings where it
> saves off the source string in field in the helper structure[1], the
> assignment of that value to the trace event field is stored in the helper
> value and does not need to be passed in again.
> 
> This means that with:
> 
>   __string(field, mystring)
> 
> Which use to be assigned with __assign_str(field, mystring), no longer
> needs the second parameter and it is unused. With this, __assign_str()
> will now only get a single parameter.
> 
> There's over 700 users of __assign_str() and because coccinelle does not
> handle the TRACE_EVENT() macro I ended up using the following sed script:
> 
>   git grep -l __assign_str | while read a ; do
>       sed -e 's/\(__assign_str([^,]*[^ ,]\) *,[^;]*/\1)/' $a > /tmp/test-file;
>       mv /tmp/test-file $a;
>   done
> 
> I then searched for __assign_str() that did not end with ';' as those
> were multi line assignments that the sed script above would fail to catch.
> 
> Note, the same updates will need to be done for:
> 
>   __assign_str_len()
>   __assign_rel_str()
>   __assign_rel_str_len()
>   __assign_bitmask()
>   __assign_rel_bitmask()
>   __assign_cpumask()
>   __assign_rel_cpumask()
> 
> [1] https://lore.kernel.org/linux-trace-kernel/20240222211442.634192653@xxxxxxxxxxx/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
>  arch/arm64/kernel/trace-events-emulation.h    |   2 +-
>  arch/powerpc/include/asm/trace.h              |   4 +-
>  arch/x86/kvm/trace.h                          |   2 +-
>  drivers/base/regmap/trace.h                   |  18 +--
>  drivers/base/trace.h                          |   2 +-
>  drivers/block/rnbd/rnbd-srv-trace.h           |  12 +-
>  drivers/cxl/core/trace.h                      |  24 ++--

snip to CXL


> diff --git a/drivers/cxl/core/trace.h b/drivers/cxl/core/trace.h
> index bdf117a33744..07ba4e033347 100644
> --- a/drivers/cxl/core/trace.h
> +++ b/drivers/cxl/core/trace.h

snip to poison

> @@ -668,8 +668,8 @@ TRACE_EVENT(cxl_poison,
>  	    ),
>  
>  	TP_fast_assign(
> -		__assign_str(memdev, dev_name(&cxlmd->dev));
> -		__assign_str(host, dev_name(cxlmd->dev.parent));
> +		__assign_str(memdev);
> +		__assign_str(host);

I think I get that the above changes work because the TP_STRUCT__entry for
these did:
	__string(memdev, dev_name(&cxlmd->dev))
	__string(host, dev_name(cxlmd->dev.parent))

>  		__entry->serial = cxlmd->cxlds->serial;
>  		__entry->overflow_ts = cxl_poison_overflow(flags, overflow_ts);
>  		__entry->dpa = cxl_poison_record_dpa(record);
> @@ -678,12 +678,12 @@ TRACE_EVENT(cxl_poison,
>  		__entry->trace_type = trace_type;
>  		__entry->flags = flags;
>  		if (region) {
> -			__assign_str(region, dev_name(&region->dev));
> +			__assign_str(region);
>  			memcpy(__entry->uuid, &region->params.uuid, 16);
>  			__entry->hpa = cxl_trace_hpa(region, cxlmd,
>  						     __entry->dpa);
>  		} else {
> -			__assign_str(region, "");
> +			__assign_str(region);
>  			memset(__entry->uuid, 0, 16);
>  			__entry->hpa = ULLONG_MAX;

For the above 2, there was no helper in TP_STRUCT__entry. A recently
posted patch is fixing that up to be __string(region, NULL) See [1],
with the actual assignment still happening in TP_fast_assign.

Does that assign logic need to move to the TP_STRUCT__entry definition
when you merge these changes? I'm not clear how much logic is able to be
included, ie like 'C' style code in the TP_STRUCT__entry.

[1]
https://lore.kernel.org/linux-cxl/20240314044301.2108650-1-alison.schofield@xxxxxxxxx/

Thanks for helping,
Alison


>  		}