On 24/03/2016 09:26, Wouter Verhelst wrote: >> > >> > No, there is no specific reason. Looks like NBD_CMD_FLAG_ZEROES fits the >> > spec and implementations nicely. So I'll rewrite the extension and add >> > the flag instead of the whole command. > Actually, having given this some more thought... > > There is at least one server-side implementation of nbd (mine) which > silently ignores flags it doesn't know about. This isn't a problem for > non-critical flags, but it could be a problem for a flag like this. Of > course, a client shouldn't send a flag to a server which that server > hasn't heard of, but mistakes do happen. > > Do we want to keep that in mind? If so, we might want to keep it as a > separate command after all. > > OTOH, it could be said that silently ignoring unknown messages is a bug. > I should probably just fix my implementation instead.
Even if it is a bug, it does suggest that the payload format should not be changed by flags. For example ignoring flags is a bug for an NBD server, but not for a Wireshark protocol dissector. Paolo
