Hello kernel hackers, I noticed that in [linux]/include/uapi/linux/nbd.h the structure struct nbd_request { __be32 magic; __be32 type; /* == READ || == WRITE */ char handle[8]; __be64 from; __be32 len; } __attribute__((packed)); is packed but its reply counter part struct nbd_reply { __be32 magic; __be32 error; /* 0 = ok, else error */ char handle[8]; /* handle you got from request */ }; is not. Since Linux seems to read sizeof(nbd_reply) bytes from the network (see [1]), the number of bytes read varies with the number of bytes of the structure. So my understanding is that if the size of struct nbd_reply varies from platform/compiler to another that means trouble. I wonder: - Is there anything about struct nbd_reply that would keep its size equal everywhere or a reason why variance in size is no problem here? - Any ideas for a platform where you would expect struct nbd_reply to be other than 4 + 4 + 8 = 16 bytes in size? Best, Sebastian [1] http://lxr.linux.no/#linux+v3.7.1/drivers/block/nbd.c#L336