The FUSE protocol uses struct fuse_write_out to convey the return value of copy_file_range, which is restricted to uint32_t. But the copy_file_range interface supports a 64-bit copy operation. Given that copy_file_range is expected to clone huge files, large copies are not unexpected, so this appears to be a real limitation. There is another wrinkle: we'd need to check if the process runs in 32-bit compat mode, and reject size_t arguments larger than INT_MAX in this case (with EOVERFLOW presumably). But perhaps this should be handled on the kernel side? Currently, this doesn't seem to happen, and we can get copy_file_range results in the in-band error range. Applications have no way to disambiguate this. Thanks, Florian
