btrfs: add helper to truncate inode items when logging inode

Move the call to btrfs_truncate_inode_items(), and the surrounding retry
loop, into a local helper function. This avoids some repetition and avoids
making the next change a bit awkward due to a bit of too much indentation.

This patch is part of a patch set comprised of the following patches:

  btrfs: check if a log tree exists at inode_logged()
  btrfs: remove no longer needed checks for NULL log context
  btrfs: do not log new dentries when logging that a new name exists
  btrfs: always update the logged transaction when logging new names
  btrfs: avoid expensive search when dropping inode items from log
  btrfs: add helper to truncate inode items when logging inode
  btrfs: avoid expensive search when truncating inode items from the log
  btrfs: avoid search for logged i_size when logging inode if possible
  btrfs: avoid attempt to drop extents when logging inode for the first time
  btrfs: do not commit delayed inode when logging a file in full sync mode

This is patch 6/10 and test results are listed in the change log of the
last patch in the set.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -3937,6 +3937,21 @@ static int drop_inode_items(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+static int truncate_inode_items(struct btrfs_trans_handle *trans,
+				struct btrfs_root *log_root,
+				struct btrfs_inode *inode,
+				u64 new_size, u32 min_type)
+{
+	int ret;
+
+	do {
+		ret = btrfs_truncate_inode_items(trans, log_root, inode,
+						 new_size, min_type, NULL);
+	} while (ret == -EAGAIN);
+
+	return ret;
+}
+
 static void fill_inode_item(struct btrfs_trans_handle *trans,
 			    struct extent_buffer *leaf,
 			    struct btrfs_inode_item *item,
@@ -4525,13 +4540,9 @@ static int btrfs_log_prealloc_extents(struct btrfs_trans_handle *trans,
 			 * Avoid logging extent items logged in past fsync calls
 			 * and leading to duplicate keys in the log tree.
 			 */
-			do {
-				ret = btrfs_truncate_inode_items(trans,
-							 root->log_root,
-							 inode, truncate_offset,
-							 BTRFS_EXTENT_DATA_KEY,
-							 NULL);
-			} while (ret == -EAGAIN);
+			ret = truncate_inode_items(trans, root->log_root, inode,
+						   truncate_offset,
+						   BTRFS_EXTENT_DATA_KEY);
 			if (ret)
 				goto out;
 			dropped_extents = true;
@@ -5477,12 +5488,7 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
 					  &inode->runtime_flags);
 				clear_bit(BTRFS_INODE_COPY_EVERYTHING,
 					  &inode->runtime_flags);
-				while(1) {
-					ret = btrfs_truncate_inode_items(trans,
-						log, inode, 0, 0, NULL);
-					if (ret != -EAGAIN)
-						break;
-				}
+				ret = truncate_inode_items(trans, log, inode, 0, 0);
 			}
 		} else if (test_and_clear_bit(BTRFS_INODE_COPY_EVERYTHING,
 					      &inode->runtime_flags) ||