btrfs: drop never met disk total bytes check in verify_one_dev_extent

Drop the condition in verify_one_dev_extent,
btrfs_device::disk_total_bytes is set even for a seed device. The
comment is wrong, the size is properly set when cloning the device.

Commit 1b3922a8 ("btrfs: Use real device structure to verify
dev extent") introduced it but it's unclear why the total_disk_bytes
was 0.

Theoretically, all devices (including missing and seed) marked with the
BTRFS_DEV_STATE_IN_FS_METADATA flag gets the total_disk_bytes updated at
fill_device_from_item():

  open_ctree()
    btrfs_read_chunk_tree()
      read_one_dev()
        open_seed_device()
        fill_device_from_item()

Even if verify_one_dev_extent() reports total_disk_bytes == 0, then its
a bug to be fixed somewhere else and not in verify_one_dev_extent() as
it's just a messenger. It is never expected that a total_disk_bytes
shall be zero.

The function fill_device_from_item() does the job of reading it from the
item and updating btrfs_device::disk_total_bytes. So both the missing
device and the seed devices do have their disk_total_bytes updated.
btrfs_find_device can also return a device from fs_info->seed_list
because it searches it as well.

Furthermore, while removing the device if there is a power loss, we
could have a device with its total_bytes = 0, that's still valid.

Instead, introduce a check against maximum block device size in
read_one_dev().
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -6869,6 +6869,16 @@ static int read_one_dev(struct extent_buffer *leaf,
 	}
 
 	fill_device_from_item(leaf, dev_item, device);
+	if (device->bdev) {
+		u64 max_total_bytes = i_size_read(device->bdev->bd_inode);
+
+		if (device->total_bytes > max_total_bytes) {
+			btrfs_err(fs_info,
+			"device total_bytes should be at most %llu but found %llu",
+				  max_total_bytes, device->total_bytes);
+			return -EINVAL;
+		}
+	}
 	set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
 	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
 	   !test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
@@ -7598,21 +7608,6 @@ static int verify_one_dev_extent(struct btrfs_fs_info *fs_info,
 		goto out;
 	}
 
-	/* It's possible this device is a dummy for seed device */
-	if (dev->disk_total_bytes == 0) {
-		struct btrfs_fs_devices *devs;
-
-		devs = list_first_entry(&fs_info->fs_devices->seed_list,
-					struct btrfs_fs_devices, seed_list);
-		dev = btrfs_find_device(devs, devid, NULL, NULL, false);
-		if (!dev) {
-			btrfs_err(fs_info, "failed to find seed devid %llu",
-				  devid);
-			ret = -EUCLEAN;
-			goto out;
-		}
-	}
-
 	if (physical_offset + physical_len > dev->disk_total_bytes) {
 		btrfs_err(fs_info,
 "dev extent devid %llu physical offset %llu len %llu is beyond device boundary %llu",