Re: Retrieving CSUM-Tree

Tobias Reinhard
2019-01-25T17:00:03Z

Am 13.01.2019 um 12:02 schrieb Qu Wenruo:
>
> On 2019/1/13 下午6:19, Tobias Reinhard wrote:
>> Hi,
>>
>> I want to read the complete CSUM-Tree from userspace. I tried it via the
>> ioctl. This is what the code looks like:
>>
>> struct btrfs_sv2_args sv2_args;
>> int fd = open(filename, O_RDONLY);
>> sv2_args.key.tree_id = BTRFS_CSUM_TREE_OBJECTID;
>> sv2_args.key.min_objectid = 0;
>> sv2_args.key.max_objectid = -1;
>> sv2_args.key.min_offset = 0;
>> sv2_args.key.max_offset = -1;
>> sv2_args.key.min_transid = 0;
>> sv2_args.key.max_transid = -1;
>> sv2_args.key.min_type = BTRFS_CSUM_ITEM_KEY;
>> sv2_args.key.max_type = BTRFS_CSUM_ITEM_KEY;
>> sv2_args.key.nr_items = -1;
>> sv2_args.buf_size = sizeof(sv2_args.buf);
>> ioctl(fd, BTRFS_IOC_TREE_SEARCH_V2, &sv2_args);
>>
>> But the device is not small and I hit the limit of the
>> btrfs_sv2_args.buf which seems to be 16 MB.
>>
>> How can I get the *complete* CSUM-Tree?
>>
>> Limiting to offset does not work (My first idea was to do it this way
>> and get it in chunks).
> That's strange.
>
> Are you still using 0~-1 objectid and 0~-1 type, just last_offset~-1?
>
> Have tried searching using the following parameters?
> min_objectid = max_objectid = BTRFS_EXTENT_CSUM_OBJECTID
> min_type = max_type = BTRFS_CSUM_ITEM_KEY;
> min_offset = last_found_csum_offset
> max_offset = -1

Sorry for my late response.

If I set

min_objectid = max_objectid = BTRFS_EXTENT_CSUM_OBJECTID

I don't get anything. I have to set it to max=-1 (min doesn't matter).

And in that I case, min_offset and max_offset doesn't matter - I always
get the same result. I can even use "wrong" filters like min=1000 max=500.

Tobias