Re: [PATCH v3 14/18] libtraceeval histogram: Use stack for old copy in update

[Ross Zwisler <zwisler@google.com>]

On Thu, Aug 17, 2023 at 03:42:45PM -0400, Steven Rostedt wrote:
> On Thu, 17 Aug 2023 13:29:26 -0600
> Ross Zwisler <zwisler@google.com> wrote:
> 
> > > + fail:
> > > +	/* Free the new values that were added */
> > > +	data_release(i, copy, types);
> > > +	/* Put back the old values */
> > > +	for (i--; i >= 0; i--) {
> > > +		copy_traceeval_data(types + i, NULL,
> > > +				    copy + i, old + i);  
> > 
> > should be:                          old + i, copy + i);
> > 
> > Right now we're copying 'copy' into 'old', but we want to be doing it the
> > other way around so we restore 'copy' back to its saved state in 'old'
> 
> I need to change the parameter names to "src" and "dst" as I can't think of
> "orig" and "copy" as which direction they go. 

I was thinking the same thing, 'src' and 'dst' would be better. :)

> I looked at that three times,
> and still am confused. And probably reverse them too to make it equivalent
> to memcpy():
> 
> From memcpy() man page;
> 
> SYNOPSIS
>        #include <string.h>
> 
>        void *memcpy(void *restrict dest, const void *restrict src, size_t n);
> 
> DESCRIPTION
>        The memcpy() function copies n bytes from memory area src to memory
>        area dest.  The memory areas must not overlap.  Use memmove(3) if
>        the memory areas do overlap.
> 
> As most standard libraries have it "dst, src" I'm pretty much thinking that
> way, and my "direction" is always dst = src --> dst, src. And that's
> exactly what I was thinking above :-p
> 
> -- Steve
>