tracing: Add bitmask-list option for human-readable bitmask display

Add support for displaying bitmasks in human-readable list format (e.g.,
0,2-5,7) in addition to the default hexadecimal bitmap representation.
This is particularly useful when tracing CPU masks and other large
bitmasks where individual bit positions are more meaningful than their
hexadecimal encoding.

When the "bitmask-list" option is enabled, the printk "%*pbl" format
specifier is used to render bitmasks as comma-separated ranges, making
trace output easier to interpret for complex CPU configurations and
large bitmask values.

Link: https://patch.msgid.link/20251226160724.2246493-2-atomlin@atomlin.com
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

3 files changed, 56 insertions, 4 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b6d42fe06115..8888fc9335b6 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1411,6 +1411,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 		C(COPY_MARKER,		"copy_trace_marker"),	\
 		C(PAUSE_ON_TRACE,	"pause-on-trace"),	\
 		C(HASH_PTR,		"hash-ptr"),	/* Print hashed pointer */ \
+		C(BITMASK_LIST,		"bitmask-list"),	\
 		FUNCTION_FLAGS					\
 		FGRAPH_FLAGS					\
 		STACK_FLAGS					\
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index cc2d3306bb60..1996d7aba038 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -194,13 +194,37 @@ trace_print_symbols_seq_u64(struct trace_seq *p, unsigned long long val,
 EXPORT_SYMBOL(trace_print_symbols_seq_u64);
 #endif
 
+/**
+ * trace_print_bitmask_seq - print a bitmask to a sequence buffer
+ * @iter: The trace iterator for the current event instance
+ * @bitmask_ptr: The pointer to the bitmask data
+ * @bitmask_size: The size of the bitmask in bytes
+ *
+ * Prints a bitmask into a sequence buffer as either a hex string or a
+ * human-readable range list, depending on the instance's "bitmask-list"
+ * trace option. The bitmask is formatted into the iterator's temporary
+ * scratchpad rather than the primary sequence buffer. This avoids
+ * duplication and pointer-collision issues when the returned string is
+ * processed by a "%s" specifier in a TP_printk() macro.
+ *
+ * Returns a pointer to the formatted string within the temporary buffer.
+ */
 const char *
-trace_print_bitmask_seq(struct trace_seq *p, void *bitmask_ptr,
+trace_print_bitmask_seq(struct trace_iterator *iter, void *bitmask_ptr,
 			unsigned int bitmask_size)
 {
-	const char *ret = trace_seq_buffer_ptr(p);
+	struct trace_seq *p = &iter->tmp_seq;
+	const struct trace_array *tr = iter->tr;
+	const char *ret;
+
+	trace_seq_init(p);
+	ret = trace_seq_buffer_ptr(p);
+
+	if (tr->trace_flags & TRACE_ITER(BITMASK_LIST))
+		trace_seq_bitmask_list(p, bitmask_ptr, bitmask_size * 8);
+	else
+		trace_seq_bitmask(p, bitmask_ptr, bitmask_size * 8);
 
-	trace_seq_bitmask(p, bitmask_ptr, bitmask_size * 8);
 	trace_seq_putc(p, 0);
 
 	return ret;
diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
index 32684ef4fb9d..85f6f10d107f 100644
--- a/kernel/trace/trace_seq.c
+++ b/kernel/trace/trace_seq.c
@@ -106,7 +106,7 @@ EXPORT_SYMBOL_GPL(trace_seq_printf);
  * Writes a ASCII representation of a bitmask string into @s.
  */
 void trace_seq_bitmask(struct trace_seq *s, const unsigned long *maskp,
-		      int nmaskbits)
+		       int nmaskbits)
 {
 	unsigned int save_len = s->seq.len;
 
@@ -125,6 +125,33 @@ void trace_seq_bitmask(struct trace_seq *s, const unsigned long *maskp,
 EXPORT_SYMBOL_GPL(trace_seq_bitmask);
 
 /**
+ * trace_seq_bitmask_list - write a bitmask array in its list representation
+ * @s:		trace sequence descriptor
+ * @maskp:	points to an array of unsigned longs that represent a bitmask
+ * @nmaskbits:	The number of bits that are valid in @maskp
+ *
+ * Writes a list representation (e.g., 0-3,5-7) of a bitmask string into @s.
+ */
+void trace_seq_bitmask_list(struct trace_seq *s, const unsigned long *maskp,
+		       int nmaskbits)
+{
+	unsigned int save_len = s->seq.len;
+
+	if (s->full)
+		return;
+
+	__trace_seq_init(s);
+
+	seq_buf_printf(&s->seq, "%*pbl", nmaskbits, maskp);
+
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
+		s->full = 1;
+	}
+}
+EXPORT_SYMBOL_GPL(trace_seq_bitmask_list);
+
+/**
  * trace_seq_vprintf - sequence printing of trace information
  * @s: trace sequence descriptor
  * @fmt: printf format string