[PATCH] btrfs: get the accurate value of used_bytes in btrfs_get_block_group_info().

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

Reproducer:
	# mkfs.btrfs -f -b 20G /dev/sdb
	# mount /dev/sdb /mnt/test
	# fallocate  -l 17G /mnt/test/largefile
	# btrfs fi df /mnt/test
	Data, single: total=17.49GiB, used=6.00GiB <- only 6G, but actually it should be 17G.
	System, DUP: total=8.00MiB, used=16.00KiB
	System, single: total=4.00MiB, used=0.00B
	Metadata, DUP: total=1.00GiB, used=112.00KiB
	Metadata, single: total=8.00MiB, used=0.00B
	GlobalReserve, single: total=16.00MiB, used=0.00B
	# sync
	# btrfs fi df /mnt/test
	Data, single: total=17.49GiB, used=17.00GiB <- After sync, it is expected.
	System, DUP: total=8.00MiB, used=16.00KiB
	System, single: total=4.00MiB, used=0.00B
	Metadata, DUP: total=1.00GiB, used=112.00KiB
	Metadata, single: total=8.00MiB, used=0.00B
	GlobalReserve, single: total=16.00MiB, used=0.00B

The value of 6.00GiB is actually calculated in btrfs_get_block_group_info()
by adding the @block_group->item->used for each group together. In this way,
it did not consider the bytes in cache.

This patch adds the value of @pinned, @reserved and @bytes_super in
struct btrfs_block_group_cache to make sure we can get the accurate @used_bytes.

Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
---
 fs/btrfs/ioctl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 33c80f5..bc2aaeb 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3892,6 +3892,10 @@ void btrfs_get_block_group_info(struct list_head *groups_list,
 		space->total_bytes += block_group->key.offset;
 		space->used_bytes +=
 			btrfs_block_group_used(&block_group->item);
+		/* Add bytes-info in cache */
+		space->used_bytes += block_group->pinned;
+		space->used_bytes += block_group->reserved;
+		space->used_bytes += block_group->bytes_super;
 	}
 }
 
-- 
1.8.4.2