Re: [Libguestfs] [RFC PATCH] protocol: Add NBD_CMD_FLAG_FAST_ZERO

So I had a think about this. Isn't this easier/better solved by lifting the 32 bit restriction on the size of certain non-data requests (ie. NBD_CMD_BLOCK_STATUS, NBD_CMD_TRIM, NBD_CMD_WRITE_ZEROES). The client can then query the disk efficiently to see if it starts as zeroes, and can decide on the basis of that whether it needs to "infill" zeroes as it goes along, or can ignore zeroes because they are already zero. While at the same time lifting this restriction also solves other problems we have, notably the 32 bit limitation on trims which affects large mkfs greatly. Previously discussed here: https://lists.debian.org/nbd/2018/09/msg00001.html & continuing the next month here: https://lists.debian.org/nbd/2018/10/msg00000.html