lib/string.c: introduce memchr_inv()

memchr_inv() is mainly used to check whether the whole buffer is filled
with just a specified byte.

The function name and prototype are stolen from logfs and the
implementation is from SLUB.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Matt Mackall <mpm@selenic.com>
Acked-by: Joern Engel <joern@logfs.org>
Cc: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/logfs/logfs.h

@@ -618,7 +618,6 @@ static inline int logfs_buf_recover(struct logfs_area *area, u64 ofs,
 struct page *emergency_read_begin(struct address_space *mapping, pgoff_t index);
 void emergency_read_end(struct page *page);
 void logfs_crash_dump(struct super_block *sb);
-void *memchr_inv(const void *s, int c, size_t n);
 int logfs_statfs(struct dentry *dentry, struct kstatfs *stats);
 int logfs_check_ds(struct logfs_disk_super *ds);
 int logfs_write_sb(struct super_block *sb);

fs/logfs/super.c

@@ -90,28 +90,6 @@ void logfs_crash_dump(struct super_block *sb)
 	dump_segfile(sb);
 }
 
-/*
- * TODO: move to lib/string.c
- */
-/**
- * memchr_inv - Find a character in an area of memory.
- * @s: The memory area
- * @c: The byte to search for
- * @n: The size of the area.
- *
- * returns the address of the first character other than @c, or %NULL
- * if the whole buffer contains just @c.
- */
-void *memchr_inv(const void *s, int c, size_t n)
-{
-	const unsigned char *p = s;
-	while (n-- != 0)
-		if ((unsigned char)c != *p++)
-			return (void *)(p - 1);
-
-	return NULL;
-}
-
 /*
  * FIXME: There should be a reserve for root, similar to ext2.
  */

include/linux/string.h

@@ -114,6 +114,7 @@ extern int memcmp(const void *,const void *,__kernel_size_t);
 #ifndef __HAVE_ARCH_MEMCHR
 extern void * memchr(const void *,int,__kernel_size_t);
 #endif
+void *memchr_inv(const void *s, int c, size_t n);
 
 extern char *kstrdup(const char *s, gfp_t gfp);
 extern char *kstrndup(const char *s, size_t len, gfp_t gfp);

lib/string.c

@@ -756,3 +756,57 @@ void *memchr(const void *s, int c, size_t n)
 }
 EXPORT_SYMBOL(memchr);
 #endif
+
+static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)
+{
+	while (bytes) {
+		if (*start != value)
+			return (void *)start;
+		start++;
+		bytes--;
+	}
+	return NULL;
+}
+
+/**
+ * memchr_inv - Find an unmatching character in an area of memory.
+ * @start: The memory area
+ * @c: Find a character other than c
+ * @bytes: The size of the area.
+ *
+ * returns the address of the first character other than @c, or %NULL
+ * if the whole buffer contains just @c.
+ */
+void *memchr_inv(const void *start, int c, size_t bytes)
+{
+	u8 value = c;
+	u64 value64;
+	unsigned int words, prefix;
+
+	if (bytes <= 16)
+		return check_bytes8(start, value, bytes);
+
+	value64 = value | value << 8 | value << 16 | value << 24;
+	value64 = (value64 & 0xffffffff) | value64 << 32;
+	prefix = 8 - ((unsigned long)start) % 8;
+
+	if (prefix) {
+		u8 *r = check_bytes8(start, value, prefix);
+		if (r)
+			return r;
+		start += prefix;
+		bytes -= prefix;
+	}
+
+	words = bytes / 8;
+
+	while (words) {
+		if (*(u64 *)start != value64)
+			return check_bytes8(start, value, 8);
+		start += 8;
+		words--;
+	}
+
+	return check_bytes8(start, value, bytes % 8);
+}
+EXPORT_SYMBOL(memchr_inv);

mm/slub.c

@@ -655,49 +655,6 @@ static void init_object(struct kmem_cache *s, void *object, u8 val)
 		memset(p + s->objsize, val, s->inuse - s->objsize);
 }
 
-static u8 *check_bytes8(u8 *start, u8 value, unsigned int bytes)
-{
-	while (bytes) {
-		if (*start != value)
-			return start;
-		start++;
-		bytes--;
-	}
-	return NULL;
-}
-
-static u8 *check_bytes(u8 *start, u8 value, unsigned int bytes)
-{
-	u64 value64;
-	unsigned int words, prefix;
-
-	if (bytes <= 16)
-		return check_bytes8(start, value, bytes);
-
-	value64 = value | value << 8 | value << 16 | value << 24;
-	value64 = (value64 & 0xffffffff) | value64 << 32;
-	prefix = 8 - ((unsigned long)start) % 8;
-
-	if (prefix) {
-		u8 *r = check_bytes8(start, value, prefix);
-		if (r)
-			return r;
-		start += prefix;
-		bytes -= prefix;
-	}
-
-	words = bytes / 8;
-
-	while (words) {
-		if (*(u64 *)start != value64)
-			return check_bytes8(start, value, 8);
-		start += 8;
-		words--;
-	}
-
-	return check_bytes8(start, value, bytes % 8);
-}
-
 static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
 						void *from, void *to)
 {
@@ -712,7 +669,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
 	u8 *fault;
 	u8 *end;
 
-	fault = check_bytes(start, value, bytes);
+	fault = memchr_inv(start, value, bytes);
 	if (!fault)
 		return 1;
 
@@ -805,7 +762,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 	if (!remainder)
 		return 1;
 
-	fault = check_bytes(end - remainder, POISON_INUSE, remainder);
+	fault = memchr_inv(end - remainder, POISON_INUSE, remainder);
 	if (!fault)
 		return 1;
 	while (end > fault && end[-1] == POISON_INUSE)