ext4: eliminate xattr entry e_hash recalculation for removes

When an extended attribute block is modified, ext4_xattr_hash_entry()
recalculates e_hash for the entry that is pointed by s->here. This  is
unnecessary if the modification is to remove an entry.

Currently, if the removed entry is the last one and there are other
entries remaining, hash calculation targets the just erased entry which
has been filled with zeroes and effectively does nothing.  If the removed
entry is not the last one and there are more entries, this time it will
recalculate hash on the next entry which is totally unnecessary.

Fix these by moving the decision on when to recalculate hash to
ext4_xattr_set_entry().
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/xattr.c

@@ -77,8 +77,9 @@ static void ext4_xattr_block_cache_insert(struct mb_cache *,
 static struct buffer_head *
 ext4_xattr_block_cache_find(struct inode *, struct ext4_xattr_header *,
 			    struct mb_cache_entry **);
-static void ext4_xattr_rehash(struct ext4_xattr_header *,
-			      struct ext4_xattr_entry *);
+static void ext4_xattr_hash_entry(struct ext4_xattr_entry *entry,
+				  void *value_base);
+static void ext4_xattr_rehash(struct ext4_xattr_header *);
 
 static const struct xattr_handler * const ext4_xattr_handler_map[] = {
 	[EXT4_XATTR_INDEX_USER]		     = &ext4_xattr_user_handler,
@@ -1467,7 +1468,8 @@ static int ext4_xattr_inode_lookup_create(handle_t *handle, struct inode *inode,
 
 static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
 				struct ext4_xattr_search *s,
-				handle_t *handle, struct inode *inode)
+				handle_t *handle, struct inode *inode,
+				bool is_block)
 {
 	struct ext4_xattr_entry *last;
 	struct ext4_xattr_entry *here = s->here;
@@ -1531,8 +1533,8 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
 		 * attribute block so that a long value does not occupy the
 		 * whole space and prevent futher entries being added.
 		 */
-		if (ext4_has_feature_ea_inode(inode->i_sb) && new_size &&
-		    (s->end - s->base) == i_blocksize(inode) &&
+		if (ext4_has_feature_ea_inode(inode->i_sb) &&
+		    new_size && is_block &&
 		    (min_offs + old_size - new_size) <
 					EXT4_XATTR_BLOCK_RESERVE(inode)) {
 			ret = -ENOSPC;
@@ -1662,6 +1664,13 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
 		}
 		here->e_value_size = cpu_to_le32(i->value_len);
 	}
+
+	if (is_block) {
+		if (i->value)
+			ext4_xattr_hash_entry(here, s->base);
+		ext4_xattr_rehash((struct ext4_xattr_header *)s->base);
+	}
+
 	ret = 0;
 out:
 	iput(old_ea_inode);
@@ -1751,14 +1760,11 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
 			mb_cache_entry_delete(ea_block_cache, hash,
 					      bs->bh->b_blocknr);
 			ea_bdebug(bs->bh, "modifying in-place");
-			error = ext4_xattr_set_entry(i, s, handle, inode);
-			if (!error) {
-				if (!IS_LAST_ENTRY(s->first))
-					ext4_xattr_rehash(header(s->base),
-							  s->here);
+			error = ext4_xattr_set_entry(i, s, handle, inode,
+						     true /* is_block */);
+			if (!error)
 				ext4_xattr_block_cache_insert(ea_block_cache,
 							      bs->bh);
-			}
 			ext4_xattr_block_csum_set(inode, bs->bh);
 			unlock_buffer(bs->bh);
 			if (error == -EFSCORRUPTED)
@@ -1818,7 +1824,7 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
 		s->end = s->base + sb->s_blocksize;
 	}
 
-	error = ext4_xattr_set_entry(i, s, handle, inode);
+	error = ext4_xattr_set_entry(i, s, handle, inode, true /* is_block */);
 	if (error == -EFSCORRUPTED)
 		goto bad_block;
 	if (error)
@@ -1841,9 +1847,6 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
 		}
 	}
 
-	if (!IS_LAST_ENTRY(s->first))
-		ext4_xattr_rehash(header(s->base), s->here);
-
 inserted:
 	if (!IS_LAST_ENTRY(s->first)) {
 		new_bh = ext4_xattr_block_cache_find(inode, header(s->base),
@@ -2076,7 +2079,7 @@ int ext4_xattr_ibody_inline_set(handle_t *handle, struct inode *inode,
 
 	if (EXT4_I(inode)->i_extra_isize == 0)
 		return -ENOSPC;
-	error = ext4_xattr_set_entry(i, s, handle, inode);
+	error = ext4_xattr_set_entry(i, s, handle, inode, false /* is_block */);
 	if (error) {
 		if (error == -ENOSPC &&
 		    ext4_has_inline_data(inode)) {
@@ -2088,7 +2091,8 @@ int ext4_xattr_ibody_inline_set(handle_t *handle, struct inode *inode,
 			error = ext4_xattr_ibody_find(inode, i, is);
 			if (error)
 				return error;
-			error = ext4_xattr_set_entry(i, s, handle, inode);
+			error = ext4_xattr_set_entry(i, s, handle, inode,
+						     false /* is_block */);
 		}
 		if (error)
 			return error;
@@ -2114,7 +2118,7 @@ static int ext4_xattr_ibody_set(handle_t *handle, struct inode *inode,
 
 	if (EXT4_I(inode)->i_extra_isize == 0)
 		return -ENOSPC;
-	error = ext4_xattr_set_entry(i, s, handle, inode);
+	error = ext4_xattr_set_entry(i, s, handle, inode, false /* is_block */);
 	if (error)
 		return error;
 	header = IHDR(inode, ext4_raw_inode(&is->iloc));
@@ -2940,8 +2944,8 @@ ext4_xattr_block_cache_find(struct inode *inode,
  *
  * Compute the hash of an extended attribute.
  */
-static inline void ext4_xattr_hash_entry(struct ext4_xattr_header *header,
-					 struct ext4_xattr_entry *entry)
+static void ext4_xattr_hash_entry(struct ext4_xattr_entry *entry,
+				  void *value_base)
 {
 	__u32 hash = 0;
 	char *name = entry->e_name;
@@ -2954,7 +2958,7 @@ static inline void ext4_xattr_hash_entry(struct ext4_xattr_header *header,
 	}
 
 	if (!entry->e_value_inum && entry->e_value_size) {
-		__le32 *value = (__le32 *)((char *)header +
+		__le32 *value = (__le32 *)((char *)value_base +
 			le16_to_cpu(entry->e_value_offs));
 		for (n = (le32_to_cpu(entry->e_value_size) +
 		     EXT4_XATTR_ROUND) >> EXT4_XATTR_PAD_BITS; n; n--) {
@@ -2976,13 +2980,11 @@ static inline void ext4_xattr_hash_entry(struct ext4_xattr_header *header,
  *
  * Re-compute the extended attribute hash value after an entry has changed.
  */
-static void ext4_xattr_rehash(struct ext4_xattr_header *header,
-			      struct ext4_xattr_entry *entry)
+static void ext4_xattr_rehash(struct ext4_xattr_header *header)
 {
 	struct ext4_xattr_entry *here;
 	__u32 hash = 0;
 
-	ext4_xattr_hash_entry(header, entry);
 	here = ENTRY(header+1);
 	while (!IS_LAST_ENTRY(here)) {
 		if (!here->e_hash) {