btrfs: Round down values which are written for total_bytes_size

We got an internal report about a file system not wanting to mount
following 99e3ecfc ("Btrfs: add more validation checks for
superblock").

BTRFS error (device sdb1): super_total_bytes 1000203816960 mismatch with
fs_devices total_rw_bytes 1000203820544

Subtracting the numbers we get a difference of less than a 4kb. Upon
closer inspection it became apparent that mkfs actually rounds down the
size of the device to a multiple of sector size. However, the same
cannot be said for various functions which modify the total size and are
called from btrfs_balance as well as when adding a new device. So this
patch ensures that values being saved into on-disk data structures are
always rounded down to a multiple of sectorsize.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -1556,6 +1556,7 @@ static inline void btrfs_set_device_total_bytes(struct extent_buffer *eb,
 {
 	BUILD_BUG_ON(sizeof(u64) !=
 		     sizeof(((struct btrfs_dev_item *)0))->total_bytes);
+	WARN_ON(!IS_ALIGNED(val, eb->fs_info->sectorsize));
 	btrfs_set_64(eb, s, offsetof(struct btrfs_dev_item, total_bytes), val);
 }
 

fs/btrfs/volumes.c

@@ -2385,7 +2385,8 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 	device->io_width = fs_info->sectorsize;
 	device->io_align = fs_info->sectorsize;
 	device->sector_size = fs_info->sectorsize;
-	device->total_bytes = i_size_read(bdev->bd_inode);
+	device->total_bytes = round_down(i_size_read(bdev->bd_inode),
+					 fs_info->sectorsize);
 	device->disk_total_bytes = device->total_bytes;
 	device->commit_total_bytes = device->total_bytes;
 	device->fs_info = fs_info;
@@ -2422,7 +2423,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 
 	tmp = btrfs_super_total_bytes(fs_info->super_copy);
 	btrfs_set_super_total_bytes(fs_info->super_copy,
-				    tmp + device->total_bytes);
+		round_down(tmp + device->total_bytes, fs_info->sectorsize));
 
 	tmp = btrfs_super_num_devices(fs_info->super_copy);
 	btrfs_set_super_num_devices(fs_info->super_copy, tmp + 1);
@@ -2685,6 +2686,8 @@ int btrfs_grow_device(struct btrfs_trans_handle *trans,
 	if (!device->writeable)
 		return -EACCES;
 
+	new_size = round_down(new_size, fs_info->sectorsize);
+
 	mutex_lock(&fs_info->chunk_mutex);
 	old_total = btrfs_super_total_bytes(super_copy);
 	diff = new_size - device->total_bytes;
@@ -2697,7 +2700,8 @@ int btrfs_grow_device(struct btrfs_trans_handle *trans,
 
 	fs_devices = fs_info->fs_devices;
 
-	btrfs_set_super_total_bytes(super_copy, old_total + diff);
+	btrfs_set_super_total_bytes(super_copy,
+			round_down(old_total + diff, fs_info->sectorsize));
 	device->fs_devices->total_rw_bytes += diff;
 
 	btrfs_device_set_total_bytes(device, new_size);
@@ -4387,7 +4391,10 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 	struct btrfs_super_block *super_copy = fs_info->super_copy;
 	u64 old_total = btrfs_super_total_bytes(super_copy);
 	u64 old_size = btrfs_device_get_total_bytes(device);
-	u64 diff = old_size - new_size;
+	u64 diff;
+
+	new_size = round_down(new_size, fs_info->sectorsize);
+	diff = old_size - new_size;
 
 	if (device->is_tgtdev_for_dev_replace)
 		return -EINVAL;
@@ -4514,7 +4521,8 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 			      &fs_info->fs_devices->resized_devices);
 
 	WARN_ON(diff > old_total);
-	btrfs_set_super_total_bytes(super_copy, old_total - diff);
+	btrfs_set_super_total_bytes(super_copy,
+			round_down(old_total - diff, fs_info->sectorsize));
 	mutex_unlock(&fs_info->chunk_mutex);
 
 	/* Now btrfs_update_device() will change the on-disk size. */