[v6,6/9] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul}

Commit Message

Yafang Shao Aug. 12, 2024, 2:29 a.m. UTC

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

Suggested-by: Andrew Morton <[e-mail]>
Signed-off-by: Yafang Shao <[e-mail]>
Cc: Simon Horman <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
---
 mm/util.c | 67 +++++++++++++++++++++----------------------------------
 1 file changed, 26 insertions(+), 41 deletions(-)

Patch

diff --git a/mm/util.c b/mm/util.c
index 4542d8a800d9..310c7735c617 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -45,33 +45,40 @@  void kfree_const(const void *x)
 EXPORT_SYMBOL(kfree_const);
 
 /**
- * kstrdup - allocate space for and copy an existing string
- * @s: the string to duplicate
+ * __kmemdup_nul - Create a NUL-terminated string from @s, which might be unterminated.
+ * @s: The data to copy
+ * @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 or %NULL in case of error
+ * Return: newly allocated copy of @s with NUL-termination or %NULL in
+ * case of error
  */
-noinline
-char *kstrdup(const char *s, gfp_t gfp)
+static __always_inline char *__kmemdup_nul(const char *s, size_t len, gfp_t gfp)
 {
-	size_t len;
 	char *buf;
 
-	if (!s)
+	buf = kmalloc_track_caller(len, gfp);
+	if (!buf)
 		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';
-	}
+	memcpy(buf, s, len);
+	/* Ensure the buf is always NUL-terminated, regardless of @s. */
+	buf[len - 1] = '\0';
 	return buf;
 }
+
+/**
+ * kstrdup - allocate space for and copy an existing string
+ * @s: the string to duplicate
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ *
+ * Return: newly allocated copy of @s or %NULL in case of error
+ */
+noinline
+char *kstrdup(const char *s, gfp_t gfp)
+{
+	return s ? __kmemdup_nul(s, strlen(s) + 1, gfp) : NULL;
+}
 EXPORT_SYMBOL(kstrdup);
 
 /**
@@ -106,19 +113,7 @@  EXPORT_SYMBOL(kstrdup_const);
  */
 char *kstrndup(const char *s, size_t max, gfp_t gfp)
 {
-	size_t len;
-	char *buf;
-
-	if (!s)
-		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 s ? __kmemdup_nul(s, strnlen(s, max) + 1, gfp) : NULL;
 }
 EXPORT_SYMBOL(kstrndup);
 
@@ -192,17 +187,7 @@  EXPORT_SYMBOL(kvmemdup);
  */
 char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
 {
-	char *buf;
-
-	if (!s)
-		return NULL;
-
-	buf = kmalloc_track_caller(len + 1, gfp);
-	if (buf) {
-		memcpy(buf, s, len);
-		buf[len] = '\0';
-	}
-	return buf;
+	return s ? __kmemdup_nul(s, len + 1, gfp) : NULL;
 }
 EXPORT_SYMBOL(kmemdup_nul);