Hello, I just found a cool feature in Btrfs for cloning partially source file to the destination by specifying the desired offset and length to be copied.
The call interface is something like below: struct btrfs_clone_range_args cr; cr.src_fd = source_desc; cr.src_offset = (uint64_t) offset; cr.src_length = (uint64_t) length; cr.dest_offset = (uint64_t) d_offset; ioctl(dest_fd, BTRFS_IOC_CLONE_RANGE, &args); cp(1) has already works with "reflink" supported for a long time, IMHO, this new feature could improve it to some extent. Is it acceptable to add a new option like "--reflink-range=src_offset,src_length,dst_offset" to clone partially source file? In this way, if reflink-range is triggered, cp(1) will try to parse the offset and length which are separated by comma, then try to clone src_length bytes from src_offset to the destination file started at dst_offset. if reflink-range failed, just let cp(1) fail with appropriate error info. I'd like to implement it if you guys think it does make sense. :-P. Thanks, -Jeff
