Re: [RFC ONLY 3/8] btrfs: read raid-stripe-tree from disk

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 17/05/2022 10:10, Qu Wenruo wrote:
> 
> 
> On 2022/5/16 22:31, Johannes Thumshirn wrote:
>> If we're discovering a raid-stripe-tree on mount, read it from disk.
>>
>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>> ---
>>   fs/btrfs/ctree.h           |  1 +
>>   fs/btrfs/disk-io.c         | 12 ++++++++++++
>>   include/uapi/linux/btrfs.h |  1 +
>>   3 files changed, 14 insertions(+)
>>
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index 20aa2ebac7cd..1db669662f61 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -667,6 +667,7 @@ struct btrfs_fs_info {
>>   	struct btrfs_root *uuid_root;
>>   	struct btrfs_root *data_reloc_root;
>>   	struct btrfs_root *block_group_root;
>> +	struct btrfs_root *stripe_root;
>>
>>   	/* the log root tree is a directory of all the other log roots */
>>   	struct btrfs_root *log_root_tree;
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index d456f426924c..c0f08917465a 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -1706,6 +1706,9 @@ static struct btrfs_root *btrfs_get_global_root(struct btrfs_fs_info *fs_info,
>>
>>   		return btrfs_grab_root(root) ? root : ERR_PTR(-ENOENT);
>>   	}
>> +	if (objectid == BTRFS_RAID_STRIPE_TREE_OBJECTID)
>> +		return btrfs_grab_root(fs_info->stripe_root) ?
>> +			fs_info->stripe_root : ERR_PTR(-ENOENT);
>>   	return NULL;
>>   }
>>
>> @@ -1784,6 +1787,7 @@ void btrfs_free_fs_info(struct btrfs_fs_info *fs_info)
>>   	btrfs_put_root(fs_info->fs_root);
>>   	btrfs_put_root(fs_info->data_reloc_root);
>>   	btrfs_put_root(fs_info->block_group_root);
>> +	btrfs_put_root(fs_info->stripe_root);
>>   	btrfs_check_leaked_roots(fs_info);
>>   	btrfs_extent_buffer_leak_debug_check(fs_info);
>>   	kfree(fs_info->super_copy);
>> @@ -2337,6 +2341,7 @@ static void free_root_pointers(struct btrfs_fs_info *info, bool free_chunk_root)
>>   	free_root_extent_buffers(info->fs_root);
>>   	free_root_extent_buffers(info->data_reloc_root);
>>   	free_root_extent_buffers(info->block_group_root);
>> +	free_root_extent_buffers(info->stripe_root);
>>   	if (free_chunk_root)
>>   		free_root_extent_buffers(info->chunk_root);
>>   }
>> @@ -2773,6 +2778,13 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
>>   		fs_info->uuid_root = root;
>>   	}
>>
> 
> I guess in the real patch, we need to check the incompatble feature first.

Or at least a compatible_ro. For regular drives it should be sufficient, for
zoned drives mounting with raid without a stripe tree will fail.

> 
> Another problem is, how do we do bootstrap?
> 
> If our metadata (especially chunk tree) is also in some chunks which is
> stripe-tree mapped, without stripe tree we're even unable to read the
> chunk tree.
> 
> Or do you plan to not support metadata on stripe-tree mapped chunks?

I do, but I have no clue yet how to attack this problem. I was hoping to get some
insights from Josef's extent-tree v2 series.

Metadata on the stripe tree really is the main blocker right now.