[PATCH v3 06/11] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul}

[Yafang Shao <laoar.shao@gmail.com>]

These three functions follow the same pattern. To deduplicate the code,
let's introduce a common help __kstrndup().

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 mm/internal.h | 24 ++++++++++++++++++++++++
 mm/util.c     | 27 ++++-----------------------
 2 files changed, 28 insertions(+), 23 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index b2c75b12014e..fd87f685739b 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1521,4 +1521,28 @@ static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
 void workingset_update_node(struct xa_node *node);
 extern struct list_lru shadow_nodes;
 
+/**
+ * __kstrndup - Create a NUL-terminated string from @s, which might be unterminated.
+ * @s: The data to stringify
+ * @len: The size of the data, including the null terminator
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ *
+ * Return: newly allocated copy of @s with NUL-termination or %NULL in
+ * case of error
+ */
+static __always_inline char *__kstrndup(const char *s, size_t len, gfp_t gfp)
+{
+	char *buf;
+
+	buf = kmalloc_track_caller(len, gfp);
+	if (!buf)
+		return NULL;
+
+	memcpy(buf, s, len);
+	/* Ensure the buf is always NUL-terminated, regardless of @s. */
+	buf[len - 1] = '\0';
+	return buf;
+}
+
+
 #endif	/* __MM_INTERNAL_H */
diff --git a/mm/util.c b/mm/util.c
index 41c7875572ed..d9135c5fdf7f 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -58,17 +58,8 @@ char *kstrdup(const char *s, gfp_t gfp)
 	if (!s)
 		return NULL;
 
-	len = strlen(s) + 1;
-	buf = kmalloc_track_caller(len, gfp);
-	if (buf) {
-		memcpy(buf, s, len);
-		/* During memcpy(), the string might be updated to a new value,
-		 * which could be longer than the string when strlen() is
-		 * called. Therefore, we need to add a null termimator.
-		 */
-		buf[len - 1] = '\0';
-	}
-	return buf;
+	len = strlen(s);
+	return __kstrndup(s, len + 1, gfp);
 }
 EXPORT_SYMBOL(kstrdup);
 
@@ -111,12 +102,7 @@ char *kstrndup(const char *s, size_t max, gfp_t gfp)
 		return NULL;
 
 	len = strnlen(s, max);
-	buf = kmalloc_track_caller(len+1, gfp);
-	if (buf) {
-		memcpy(buf, s, len);
-		buf[len] = '\0';
-	}
-	return buf;
+	return __kstrndup(s, len + 1, gfp);
 }
 EXPORT_SYMBOL(kstrndup);
 
@@ -195,12 +181,7 @@ char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
 	if (!s)
 		return NULL;
 
-	buf = kmalloc_track_caller(len + 1, gfp);
-	if (buf) {
-		memcpy(buf, s, len);
-		buf[len] = '\0';
-	}
-	return buf;
+	return __kstrndup(s, len + 1, gfp);
 }
 EXPORT_SYMBOL(kmemdup_nul);
 
-- 
2.39.1