On 6/11/19 9:22 AM, Martin Kletzander wrote: > On Tue, Jun 11, 2019 at 12:53:30PM +0100, Richard W.M. Jones wrote: >> For further information about discussion around this standard, see >> this thread on the mailing list: >> https://lists.debian.org/nbd/2019/05/msg00013.html >> >> +## Other NBD URI query parameters >> + >> +Clients SHOULD prefix experimental query parameters using `x-`. This >> +SHOULD NOT be used for query parameters which are expected to be >> +widely used. >> + >> +Any other query parameters which the client does not understand SHOULD >> +be ignored by the parser. >> + > > Everything seems good to me, I just have one "idea". I, however, am not > sure > whether it might be helpful or utterly stupid. But since I would never > forgive > myself not mentioning it, here goes: > > TL;DR: Is it worth to care about > versioning/some-kind-of-forward-compatibility? That may actually be a good idea. > > If there is a new query parameter added later on, which would significantly > change the behaviour (or security), then a client might want to depend > on it not > being ignored by the parser (e.g. if just ignoring it would cause a > security > concern). > > What I thought of would be another parameter that would specify which other > parameters must be supported, so that the client quits if any of them is > unknown. On the other hand it should be perfectly fine to make sure new > enough > version of the client is used. So, you're asking for some way to know that ?foo=bar is supported by the client, by having a way to fail if the client doesn't know how to parse the foo query. What if we document mandatory support for a parameter '?features=comma,list,of,names', where a client MUST fail to parse the URI if it does not recognize one of the feature names from the list given to features? Then we can have: nbd://host/?foo=bar - okay to ignore query foo= as unknown nbd://host/?foo=bar&features=foo - client MUST fail to parse URI unless it also knows how to parse the foo query parameter The initial set of features mandated by the NBD URI spec is 'features' for self-description, as well as 'socket' for Unix but not necessarily TCP. Then the queries '?features=' and '?features=features' must both succeed, the query '?features=socket' depends on the scheme, and any other '?features=...' query becomes a feature probe. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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