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 Thanks, Qu > > Limiting to a single transid does not work as well because even one > transid is larger than the limit. > > Kernel is 4.15. > > Any help would be appreciated. > > Best Regards > > Tobias >
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