ext4: zero out inline data using memset() instead of empty_zero_page

Not all architectures (in particular, sparc64) have empty_zero_page.
So instead of copying from empty_zero_page, use memset to clear the
inline data by signalling to ext4_xattr_set_entry() via a magic
pointer value, EXT4_ZERO_ATTR_VALUE, which is defined by casting -1 to
a pointer.

This fixes a build failure on sparc64, and the memset() should be more
efficient than using memcpy() anyway.
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inline.c

@@ -268,7 +268,7 @@ static int ext4_create_inline_data(handle_t *handle,
 		goto out;
 
 	if (len > EXT4_MIN_INLINE_DATA_SIZE) {
-		value = (void *)empty_zero_page;
+		value = EXT4_ZERO_XATTR_VALUE;
 		len -= EXT4_MIN_INLINE_DATA_SIZE;
 	} else {
 		value = "";

fs/ext4/xattr.c

@@ -628,9 +628,14 @@ ext4_xattr_set_entry(struct ext4_xattr_info *i, struct ext4_xattr_search *s)
 				   size. Just replace. */
 				s->here->e_value_size =
 					cpu_to_le32(i->value_len);
-				memset(val + size - EXT4_XATTR_PAD, 0,
-				       EXT4_XATTR_PAD); /* Clear pad bytes. */
-				memcpy(val, i->value, i->value_len);
+				if (i->value == EXT4_ZERO_XATTR_VALUE) {
+					memset(val, 0, size);
+				} else {
+					/* Clear pad bytes first. */
+					memset(val + size - EXT4_XATTR_PAD, 0,
+					       EXT4_XATTR_PAD);
+					memcpy(val, i->value, i->value_len);
+				}
 				return 0;
 			}
 
@@ -669,9 +674,14 @@ ext4_xattr_set_entry(struct ext4_xattr_info *i, struct ext4_xattr_search *s)
 			size_t size = EXT4_XATTR_SIZE(i->value_len);
 			void *val = s->base + min_offs - size;
 			s->here->e_value_offs = cpu_to_le16(min_offs - size);
-			memset(val + size - EXT4_XATTR_PAD, 0,
-			       EXT4_XATTR_PAD); /* Clear the pad bytes. */
-			memcpy(val, i->value, i->value_len);
+			if (i->value == EXT4_ZERO_XATTR_VALUE) {
+				memset(val, 0, size);
+			} else {
+				/* Clear the pad bytes first. */
+				memset(val + size - EXT4_XATTR_PAD, 0,
+				       EXT4_XATTR_PAD);
+				memcpy(val, i->value, i->value_len);
+			}
 		}
 	}
 	return 0;

fs/ext4/xattr.h

@@ -71,6 +71,7 @@ struct ext4_xattr_entry {
 #define BFIRST(bh) ENTRY(BHDR(bh)+1)
 #define IS_LAST_ENTRY(entry) (*(__u32 *)(entry) == 0)
 
+#define EXT4_ZERO_XATTR_VALUE ((void *)-1)
 
 struct ext4_xattr_info {
 	int name_index;