[PATCH v2 1/2] tracing: Add the bucket size to expr_field_str()

expr_field_str() renders a HIST_FIELD_FL_BUCKET field as "pid.buckets",
dropping the count, and parse_field() rejects that spelling.

get_hist_field_flags() returns the bare string "buckets" and keeps the
count in hist_field->buckets. hist_field_print() appends it,
expr_field_str() never did. Nothing reaches it today, since .buckets is
refused on a value and no expression can carry one, but the next patch
renders histogram keys with expr_field_str(), where a .buckets key is
legal.

Append the count, as hist_field_print() does.

Cc: stable@vger.kernel.org
Fixes: de9a48a360b7 ("tracing: Add linear buckets to histogram logic")
Signed-off-by: Donggeun Yoo <redacted>
Assisted-by: Claude:claude-fable-5
---
 kernel/trace/trace_events_hist.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 963e0d6b61fd..9d7ce01fda36 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c

@@ -1755,6 +1755,9 @@ static bool expr_field_str(struct hist_field *field, struct seq_buf *s)
 			seq_buf_printf(s, ".%s", flags_str);
 	}
 
+	if (field->buckets)
+		seq_buf_printf(s, "=%ld", field->buckets);
+
 	return !seq_buf_has_overflowed(s);
 }
 

-- 
2.53.0