Re: [Libguestfs] [PATCH libnbd] generator: Add Mutable type to the generator.

On 6/25/19 12:11 PM, Richard W.M. Jones wrote: Looks good to me. As mentioned in other threads [1], I'm interested in attempting some sort of: nbd_aio_*_callback (other args, data, callback, flags) for all transmission requests (or name it nbd_aio_*_with_notify, or whatever other name we come up with), which calls the callback the moment that particular reply from the server is ready. The ideal callback signature would thus be: int callback(void *opaque, int64_t handle, int *status) where status on input is what the server replied, and on output is what the overall nbd_aio_command_completed() will report. In the nbdkit case, I'm hoping that the callback can change things - right now, nbdkit uses the I/O polling thread to call nbd_aio_command_completed with an nbdkit lock held, and for each completed command, raise the semaphore to let the nbdkit thread that issued the request wake back up. But with the callback, the I/O polling thread doesn't ever have to grab an nbdkit lock - the callback would be the one releasing the semaphore, then the nbdkit thread that made the request would be the one also calling nbd_aio_command_completed. Also, in the case of nbd_aio_pread_structured_callback(), it also creates the nice setup of: struct pread_validator *data = generate_pread_structured_validator(offset, length, flags); handle = nbd_aio_pread_structured_callback(h, buf, count, offset, data, validate_chunk, validate_complete, flags); so that validate_complete() can call the appropriate free(data) AND do any final error manipulations (change a successful return into a failure if there were insufficient calls to validate_chunk to cover the entire buffer). [1] https://www.redhat.com/archives/libguestfs/2019-June/msg00163.html -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org