On 1/25/19 9:45 PM, Tobias Reinhard wrote: > Am 25.01.2019 um 19:05 schrieb Hans van Kranenburg: >> On 1/25/19 5:59 PM, Tobias Reinhard wrote: >>> 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. >> First, it's important to understand how all these min/max values play >> together: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/btrfs.h#n441 >> >> >> So, you define a single start key, and a single end key, and then you >> get everything that's in between (including the end value). >> >> So, this... >> >> 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; >> >> ...translates to: >> >> min key: (0, CSUM_ITEM_KEY, 0) >> max key: (18446744073709551615, CSUM_ITEM_KEY, 18446744073709551615) >> >> Since the keys end up being just a single 136 bit number, it makes no >> sense to do anything with the middle field, if the first field, objectid >> is not the same in both start and end key. The search space is linear, >> not 3 dimensional. The invidual min/max values for objectid, type and >> offset cannot be used to filter the result, they only define the >> endpoints of an interval. >> >> Since all csum items have the same objectid number anyway, the second >> suggestion is fine, and gives you this start and end: >> >> min key: (EXTENT_CSUM_OBJECTID, CSUM_ITEM_KEY, 0) >> max key: (EXTENT_CSUM_OBJECTID, CSUM_ITEM_KEY, 18446744073709551615) >> >> Works for me (here in python, but using same ioctl): >> >> -$ cat show_csum_keys.py >> #!/usr/bin/python3 >> >> import btrfs >> from btrfs.ctree import Key, CSUM_TREE_OBJECTID, \ >> EXTENT_CSUM_OBJECTID, EXTENT_CSUM_KEY >> >> with btrfs.FileSystem('/mnt/tutorial') as fs: >> min_key = Key(EXTENT_CSUM_OBJECTID, EXTENT_CSUM_KEY, 0) >> max_key = Key(EXTENT_CSUM_OBJECTID, EXTENT_CSUM_KEY + 1, 0) - 1 >> print("Searching from {} to {}".format(min_key, max_key)) >> for header, data in btrfs.ioctl.search_v2(fs.fd, CSUM_TREE_OBJECTID, >> min_key, max_key): >> print(Key(header.objectid, header.type, header.offset)) >> >> -# ./show_csum_keys.py >> Searching from (EXTENT_CSUM EXTENT_CSUM 0) to (EXTENT_CSUM EXTENT_CSUM >> -1) >> (EXTENT_CSUM EXTENT_CSUM 5700059136) >> (EXTENT_CSUM EXTENT_CSUM 5700321280) >> (EXTENT_CSUM EXTENT_CSUM 5700583424) >> (EXTENT_CSUM EXTENT_CSUM 5700845568) >> (EXTENT_CSUM EXTENT_CSUM 5701107712) >> (EXTENT_CSUM EXTENT_CSUM 5704646656) >> (EXTENT_CSUM EXTENT_CSUM 5705039872) >> (EXTENT_CSUM EXTENT_CSUM 5706350592) >> [...] >> > Reading your example, I noticed my mistake. > > I took BTRFS_CSUM_ITEM_KEY instead of BTRFS_EXTENT_CSUM_KEY for the > type, doh. > > Now, it seems to works.
Hah! Well done. I also didn't spot that. :) Probably too much CSUM dancing before our eyes... Wait until you start unpacking the search results, will only get worse... https://reactiongifs.me/wp-content/uploads/2014/06/reading-ikea-intructions-big-lebowski-confused.gif -- Hans van Kranenburg
