Read/writes IOs should be page aligned as fuse server might need to copy data to another buffer otherwise in order to fulfill network or device storage requirements. Simple reproducer is with libfuse, example/passthrough* and opening a file with O_DIRECT - without this change writing to that file failed with -EINVAL if the underlying file system was requiring alignment. Required server side changes: Server needs to seek to the next page, without splice that is just page size buffer alignment, with splice another splice syscall is needed to seek over the unaligned area. Signed-off-by: Bernd Schubert <bschubert@xxxxxxx> --- Changes since v1: - Fuse client does not send the alignment offset anymore in the write header. - Use FOPEN_ALIGNED_WRITES to be filled in by FUSE_OPEN and FUSE_CREATE instead of a FUSE_INIT flag to allow control per file and to safe init flags. - Instead of seeking a fixed offset, fuse_copy_align() just seeks to the next page. - Added sanity checks in fuse_copy_align(). libfuse patch: https://github.com/libfuse/libfuse/pull/983
