Re: [PATCH 4/9] libtraceeval: Add traceeval_iterator_remove()

[Ross Zwisler <zwisler@google.com>]

On Thu, Aug 24, 2023 at 02:19:06PM -0600, Ross Zwisler wrote:
> On Thu, Aug 17, 2023 at 06:24:17PM -0400, Steven Rostedt wrote:
> > From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> > 
> > Add an API traceeval_iterator_remove() that is safe to call in the
> > traceeval_iterator_next() loop. Currently, traceeval_remove() can also be
> > called "safely", but that may change in the future.
> > 
> > The main difference between traceeval_remove() and traceeval_iterator_remove()
> > is that that traceeval_iterator_remove() will NULL out the entry in the
> > sort array, and use this in the other iterator functions. If the entry is
> > NULL, it will not be returned.
> > 
> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> > ---
> >  include/traceeval-hist.h |  1 +
> >  src/histograms.c         | 48 ++++++++++++++++++++++++++++++++++++----
> >  2 files changed, 45 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/traceeval-hist.h b/include/traceeval-hist.h
> > index d511c9c5f14c..7d67673ce7e5 100644
> > --- a/include/traceeval-hist.h
> > +++ b/include/traceeval-hist.h
> > @@ -190,5 +190,6 @@ int traceeval_iterator_query(struct traceeval_iterator *iter,
> >  			     const union traceeval_data **results);
> >  struct traceeval_stat *traceeval_iterator_stat(struct traceeval_iterator *iter,
> >  					       struct traceeval_type *type);
> > +int traceeval_iterator_remove(struct traceeval_iterator *iter);
> >  
> >  #endif /* __LIBTRACEEVAL_HIST_H__ */
> > diff --git a/src/histograms.c b/src/histograms.c
> > index fddd0f3587e2..0fbd9e0a353e 100644
> > --- a/src/histograms.c
> > +++ b/src/histograms.c
> > @@ -1305,10 +1305,13 @@ int traceeval_iterator_next(struct traceeval_iterator *iter,
> >  		iter->next = 0;
> >  	}
> >  
> > -	if (iter->next >= iter->nr_entries)
> > -		return 0;
> > +	do {
> > +		if (iter->next >= iter->nr_entries)
> > +			return 0;
> > +
> > +		entry = iter->entries[iter->next++];
> > +	} while (!entry);
> >  
> > -	entry = iter->entries[iter->next++];
> >  	*keys = entry->keys;
> >  	return 1;
> >  }
> > @@ -1338,6 +1341,9 @@ int traceeval_iterator_query(struct traceeval_iterator *iter,
> >  		return 0;
> >  
> >  	entry = iter->entries[iter->next - 1];
> > +	if (!entry)
> > +		return 0;
> > +
> >  	*results = entry->vals;
> >  
> >  	return 1;
> > @@ -1363,5 +1369,39 @@ struct traceeval_stat *traceeval_iterator_stat(struct traceeval_iterator *iter,
> >  		return NULL;
> >  
> >  	entry = iter->entries[iter->next - 1];
> > -	return &entry->val_stats[type->index];
> > +	return entry ? &entry->val_stats[type->index] : NULL;
> > +}
> > +
> > +/**
> > + * traceeval_iterator_remove - remove the current iterator entry
> > + * @iter: The iterator to remove the entry from
> > + *
> > + * This will remove the current entry from the histogram.
> > + * This is useful if the current entry should be removed. It will not
> > + * affect the traceeval_iterator_next().
> > + *
> > + * Returns 1 if it successfully removed the entry, 0 if for some reason
> > + * there was no "current entry" (called before traceeval_iterator_next()).
> > + * or -1 on error.

Nit: we never actually return -1.  Only 1 and 0.

> > + */
> > +int traceeval_iterator_remove(struct traceeval_iterator *iter)
> > +{
> > +	struct traceeval *teval = iter->teval;
> > +	struct hash_table *hist = teval->hist;
> > +	struct entry *entry;
> > +
> > +	if (iter->next < 1 || iter->next > iter->nr_entries)
> > +		return 0;
> > +
> > +	entry = iter->entries[iter->next - 1];
> > +	if (!entry)
> > +		return 0;
> > +
> > +	hash_remove(hist, &entry->hash);
> 
> Are we leaking 'entry' after we've removed it from the hash?
> 
> I think we need to call free_entry() in both traceeval_iterator_remove() as
> well as traceeval_remove(), just like we do in the loop in
> hist_table_release().
> 
> > +
> > +	/* The entry no longer exists */
> > +	iter->entries[iter->next - 1] = NULL;
> > +	teval->update_counter++;
> > +
> > +	return 1;
> >  }
> > -- 
> > 2.40.1
> >