btrfs: open code timespec64 in struct btrfs_inode

The type of timespec64::tv_nsec is 'unsigned long', while we have only
u32 for on-disk and in-memory. This wastes a few bytes in btrfs_inode.
Add separate members for sec and nsec with the corresponding type width.
This creates a 4 byte hole in btrfs_inode which can be utilized in the
future.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -253,7 +253,8 @@ struct btrfs_inode {
 	struct btrfs_delayed_node *delayed_node;
 
 	/* File creation time. */
-	struct timespec64 i_otime;
+	u64 i_otime_sec;
+	u32 i_otime_nsec;
 
 	/* Hook into fs_info->delayed_iputs */
 	struct list_head delayed_iput;

fs/btrfs/delayed-inode.c

@@ -1847,10 +1847,8 @@ static void fill_stack_inode_item(struct btrfs_trans_handle *trans,
 	btrfs_set_stack_timespec_nsec(&inode_item->ctime,
 				      inode_get_ctime(inode).tv_nsec);
 
-	btrfs_set_stack_timespec_sec(&inode_item->otime,
-				     BTRFS_I(inode)->i_otime.tv_sec);
-	btrfs_set_stack_timespec_nsec(&inode_item->otime,
-				     BTRFS_I(inode)->i_otime.tv_nsec);
+	btrfs_set_stack_timespec_sec(&inode_item->otime, BTRFS_I(inode)->i_otime_sec);
+	btrfs_set_stack_timespec_nsec(&inode_item->otime, BTRFS_I(inode)->i_otime_nsec);
 }
 
 int btrfs_fill_inode(struct inode *inode, u32 *rdev)
@@ -1899,10 +1897,8 @@ int btrfs_fill_inode(struct inode *inode, u32 *rdev)
 	inode_set_ctime(inode, btrfs_stack_timespec_sec(&inode_item->ctime),
 			btrfs_stack_timespec_nsec(&inode_item->ctime));
 
-	BTRFS_I(inode)->i_otime.tv_sec =
-		btrfs_stack_timespec_sec(&inode_item->otime);
-	BTRFS_I(inode)->i_otime.tv_nsec =
-		btrfs_stack_timespec_nsec(&inode_item->otime);
+	BTRFS_I(inode)->i_otime_sec = btrfs_stack_timespec_sec(&inode_item->otime);
+	BTRFS_I(inode)->i_otime_nsec = btrfs_stack_timespec_nsec(&inode_item->otime);
 
 	inode->i_generation = BTRFS_I(inode)->generation;
 	BTRFS_I(inode)->index_cnt = (u64)-1;

fs/btrfs/inode.c

@@ -3771,10 +3771,8 @@ static int btrfs_read_locked_inode(struct inode *inode,
 	inode_set_ctime(inode, btrfs_timespec_sec(leaf, &inode_item->ctime),
 			btrfs_timespec_nsec(leaf, &inode_item->ctime));
 
-	BTRFS_I(inode)->i_otime.tv_sec =
-		btrfs_timespec_sec(leaf, &inode_item->otime);
-	BTRFS_I(inode)->i_otime.tv_nsec =
-		btrfs_timespec_nsec(leaf, &inode_item->otime);
+	BTRFS_I(inode)->i_otime_sec = btrfs_timespec_sec(leaf, &inode_item->otime);
+	BTRFS_I(inode)->i_otime_nsec = btrfs_timespec_nsec(leaf, &inode_item->otime);
 
 	inode_set_bytes(inode, btrfs_inode_nbytes(leaf, inode_item));
 	BTRFS_I(inode)->generation = btrfs_inode_generation(leaf, inode_item);
@@ -3944,10 +3942,8 @@ static void fill_inode_item(struct btrfs_trans_handle *trans,
 	btrfs_set_token_timespec_nsec(&token, &item->ctime,
 				      inode_get_ctime(inode).tv_nsec);
 
-	btrfs_set_token_timespec_sec(&token, &item->otime,
-				     BTRFS_I(inode)->i_otime.tv_sec);
-	btrfs_set_token_timespec_nsec(&token, &item->otime,
-				      BTRFS_I(inode)->i_otime.tv_nsec);
+	btrfs_set_token_timespec_sec(&token, &item->otime, BTRFS_I(inode)->i_otime_sec);
+	btrfs_set_token_timespec_nsec(&token, &item->otime, BTRFS_I(inode)->i_otime_nsec);
 
 	btrfs_set_token_inode_nbytes(&token, item, inode_get_bytes(inode));
 	btrfs_set_token_inode_generation(&token, item,
@@ -5609,7 +5605,8 @@ static struct inode *new_simple_dir(struct inode *dir,
 	inode->i_mode = S_IFDIR | S_IRUGO | S_IWUSR | S_IXUGO;
 	inode->i_mtime = inode_set_ctime_current(inode);
 	inode->i_atime = dir->i_atime;
-	BTRFS_I(inode)->i_otime = inode->i_mtime;
+	BTRFS_I(inode)->i_otime_sec = inode->i_mtime.tv_sec;
+	BTRFS_I(inode)->i_otime_nsec = inode->i_mtime.tv_nsec;
 	inode->i_uid = dir->i_uid;
 	inode->i_gid = dir->i_gid;
 
@@ -6286,7 +6283,8 @@ int btrfs_create_new_inode(struct btrfs_trans_handle *trans,
 
 	inode->i_mtime = inode_set_ctime_current(inode);
 	inode->i_atime = inode->i_mtime;
-	BTRFS_I(inode)->i_otime = inode->i_mtime;
+	BTRFS_I(inode)->i_otime_sec = inode->i_mtime.tv_sec;
+	BTRFS_I(inode)->i_otime_nsec = inode->i_mtime.tv_nsec;
 
 	/*
 	 * We're going to fill the inode item now, so at this point the inode
@@ -8487,8 +8485,8 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 
 	ei->delayed_node = NULL;
 
-	ei->i_otime.tv_sec = 0;
-	ei->i_otime.tv_nsec = 0;
+	ei->i_otime_sec = 0;
+	ei->i_otime_nsec = 0;
 
 	inode = &ei->vfs_inode;
 	extent_map_tree_init(&ei->extent_tree);
@@ -8642,8 +8640,8 @@ static int btrfs_getattr(struct mnt_idmap *idmap,
 	u32 bi_ro_flags = BTRFS_I(inode)->ro_flags;
 
 	stat->result_mask |= STATX_BTIME;
-	stat->btime.tv_sec = BTRFS_I(inode)->i_otime.tv_sec;
-	stat->btime.tv_nsec = BTRFS_I(inode)->i_otime.tv_nsec;
+	stat->btime.tv_sec = BTRFS_I(inode)->i_otime_sec;
+	stat->btime.tv_nsec = BTRFS_I(inode)->i_otime_nsec;
 	if (bi_flags & BTRFS_INODE_APPEND)
 		stat->attributes |= STATX_ATTR_APPEND;
 	if (bi_flags & BTRFS_INODE_COMPRESS)