From 394e05562167dfe9a28bb634b625149d01bba82e Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 12 Jun 2024 16:42:51 -0400
Subject: [PATCH] lfstack: make cds_lfs_empty argument const

cds_lfs_empty doesn't modify its argument. Hence, it can be marked as
`const`.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Iebbd1d7f2ff50ccbe36e43bec59081ce213b9a0d
---
 include/urcu/lfstack.h        | 25 +++++++++++++++++++++++--
 include/urcu/static/lfstack.h |  4 ++--
 src/lfstack.c                 |  2 +-
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/include/urcu/lfstack.h b/include/urcu/lfstack.h
index 77af43b..2a3073d 100644
--- a/include/urcu/lfstack.h
+++ b/include/urcu/lfstack.h
@@ -84,6 +84,11 @@ typedef union {
 	struct __cds_lfs_stack *_s;
 	struct cds_lfs_stack *s;
 } __attribute__((__transparent_union__)) cds_lfs_stack_ptr_t;
+
+typedef union {
+	const struct __cds_lfs_stack *_s;
+	const struct cds_lfs_stack *s;
+} __attribute__((__transparent_union__)) cds_lfs_stack_const_ptr_t;
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #endif
@@ -141,7 +146,7 @@ extern void __cds_lfs_init(struct __cds_lfs_stack *s);
  *
  * No memory barrier is issued. No mutual exclusion is required.
  */
-extern bool cds_lfs_empty(cds_lfs_stack_ptr_t s);
+extern bool cds_lfs_empty(cds_lfs_stack_const_ptr_t s);
 
 /*
  * cds_lfs_push: push a node into the stack.
@@ -276,9 +281,25 @@ static inline cds_lfs_stack_ptr_t cds_lfs_stack_cast(struct cds_lfs_stack *s)
 	return ret;
 }
 
+static inline cds_lfs_stack_const_ptr_t cds_lfs_stack_const_cast(const struct __cds_lfs_stack *s)
+{
+	cds_lfs_stack_const_ptr_t ret = {
+		._s = s,
+	};
+	return ret;
+}
+
+static inline cds_lfs_stack_const_ptr_t cds_lfs_stack_const_cast(const struct cds_lfs_stack *s)
+{
+	cds_lfs_stack_const_ptr_t ret = {
+		.s = s,
+	};
+	return ret;
+}
+
 template<typename T> static inline bool cds_lfs_empty(T s)
 {
-	return cds_lfs_empty(cds_lfs_stack_cast(s));
+	return cds_lfs_empty(cds_lfs_stack_const_cast(s));
 }
 
 template<typename T> static inline bool cds_lfs_push(T s,
diff --git a/include/urcu/static/lfstack.h b/include/urcu/static/lfstack.h
index d7e70d4..22233d8 100644
--- a/include/urcu/static/lfstack.h
+++ b/include/urcu/static/lfstack.h
@@ -87,7 +87,7 @@ void ___cds_lfs_init(struct __cds_lfs_stack *s)
 }
 
 static inline
-bool ___cds_lfs_empty_head(struct cds_lfs_head *head)
+bool ___cds_lfs_empty_head(const struct cds_lfs_head *head)
 {
 	return head == NULL;
 }
@@ -98,7 +98,7 @@ bool ___cds_lfs_empty_head(struct cds_lfs_head *head)
  * No memory barrier is issued. No mutual exclusion is required.
  */
 static inline
-bool _cds_lfs_empty(cds_lfs_stack_ptr_t s)
+bool _cds_lfs_empty(cds_lfs_stack_const_ptr_t s)
 {
 	return ___cds_lfs_empty_head(uatomic_load(&s._s->head, CMM_RELAXED));
 }
diff --git a/src/lfstack.c b/src/lfstack.c
index 5a2c80f..ca3de85 100644
--- a/src/lfstack.c
+++ b/src/lfstack.c
@@ -36,7 +36,7 @@ void __cds_lfs_init(struct __cds_lfs_stack *s)
 	___cds_lfs_init(s);
 }
 
-bool cds_lfs_empty(cds_lfs_stack_ptr_t s)
+bool cds_lfs_empty(cds_lfs_stack_const_ptr_t s)
 {
 	return _cds_lfs_empty(s);
 }
-- 
2.39.5