| Message ID | m3hbmg9qh6.fsf_-_@blackfin.pond.sub.org |
|---|---|
| State | New |
| Headers | show |
On Mon, 10 May 2010 09:16:05 +0200 Markus Armbruster <armbru@redhat.com> wrote: > Signed-off-by: Markus Armbruster <armbru@redhat.com> Looks good to me. > --- > v2: Clarify use of __RFQDN (Thanks, Luiz!) > > QMP/qmp-spec.txt | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 files changed, 55 insertions(+), 0 deletions(-) > > diff --git a/QMP/qmp-spec.txt b/QMP/qmp-spec.txt > index f3c0327..9d30a8c 100644 > --- a/QMP/qmp-spec.txt > +++ b/QMP/qmp-spec.txt > @@ -215,3 +215,58 @@ Additionally, Clients must not assume any particular: > - Order of json-object members or json-array elements > - Amount of errors generated by a command, that is, new errors can be added > to any existing command in newer versions of the Server > + > +6. Downstream extension of QMP > +------------------------------ > + > +We recommend that downstream consumers of QEMU do *not* modify QMP. > +Management tools should be able to support both upstream and downstream > +versions of QMP without special logic, and downstream extensions are > +inherently at odds with that. > + > +However, we recognize that it is sometimes impossible for downstreams to > +avoid modifying QMP. Both upstream and downstream need to take care to > +preserve long-term compatibility and interoperability. > + > +To help with that, QMP reserves JSON object member names beginning with > +'__' (double underscore) for downstream use ("downstream names"). This > +means upstream will never use any downstream names for its commands, > +arguments, errors, asynchronous events, and so forth. > + > +Any new names downstream wishes to add must begin with '__'. To > +ensure compatibility with other downstreams, it is strongly > +recommended that you prefix your downstram names with '__RFQDN_' where > +RFQDN is a valid, reverse fully qualified domain name which you > +control. For example, a qemu-kvm specific monitor command would be: > + > + (qemu) __org.linux-kvm_enable_irqchip > + > +Downstream must not change the server greeting (section 2.2) other than > +to offer additional capabilities. But see below for why even that is > +discouraged. > + > +Section '5 Compatibility Considerations' applies to downstream as well > +as to upstream, obviously. It follows that downstream must behave > +exactly like upstream for any input not containing members with > +downstream names ("downstream members"), except it may add members > +with downstream names to its output. > + > +Thus, a client should not be able to distinguish downstream from > +upstream as long as it doesn't send input with downstream members, and > +properly ignores any downstream members in the output it receives. > + > +Advice on downstream modifications: > + > +1. Introducing new commands is okay. If you want to extend an existing > + command, consider introducing a new one with the new behaviour > + instead. > + > +2. Introducing new asynchronous messages is okay. If you want to extend > + an existing message, consider adding a new one instead. > + > +3. Introducing new errors for use in new commands is okay. Adding new > + errors to existing commands counts as extension, so 1. applies. > + > +4. New capabilities are strongly discouraged. Capabilities are for > + evolving the basic protocol, and multiple diverging basic protocol > + dialects are most undesirable.
diff --git a/QMP/qmp-spec.txt b/QMP/qmp-spec.txt index f3c0327..9d30a8c 100644 --- a/QMP/qmp-spec.txt +++ b/QMP/qmp-spec.txt @@ -215,3 +215,58 @@ Additionally, Clients must not assume any particular: - Order of json-object members or json-array elements - Amount of errors generated by a command, that is, new errors can be added to any existing command in newer versions of the Server + +6. Downstream extension of QMP +------------------------------ + +We recommend that downstream consumers of QEMU do *not* modify QMP. +Management tools should be able to support both upstream and downstream +versions of QMP without special logic, and downstream extensions are +inherently at odds with that. + +However, we recognize that it is sometimes impossible for downstreams to +avoid modifying QMP. Both upstream and downstream need to take care to +preserve long-term compatibility and interoperability. + +To help with that, QMP reserves JSON object member names beginning with +'__' (double underscore) for downstream use ("downstream names"). This +means upstream will never use any downstream names for its commands, +arguments, errors, asynchronous events, and so forth. + +Any new names downstream wishes to add must begin with '__'. To +ensure compatibility with other downstreams, it is strongly +recommended that you prefix your downstram names with '__RFQDN_' where +RFQDN is a valid, reverse fully qualified domain name which you +control. For example, a qemu-kvm specific monitor command would be: + + (qemu) __org.linux-kvm_enable_irqchip + +Downstream must not change the server greeting (section 2.2) other than +to offer additional capabilities. But see below for why even that is +discouraged. + +Section '5 Compatibility Considerations' applies to downstream as well +as to upstream, obviously. It follows that downstream must behave +exactly like upstream for any input not containing members with +downstream names ("downstream members"), except it may add members +with downstream names to its output. + +Thus, a client should not be able to distinguish downstream from +upstream as long as it doesn't send input with downstream members, and +properly ignores any downstream members in the output it receives. + +Advice on downstream modifications: + +1. Introducing new commands is okay. If you want to extend an existing + command, consider introducing a new one with the new behaviour + instead. + +2. Introducing new asynchronous messages is okay. If you want to extend + an existing message, consider adding a new one instead. + +3. Introducing new errors for use in new commands is okay. Adding new + errors to existing commands counts as extension, so 1. applies. + +4. New capabilities are strongly discouraged. Capabilities are for + evolving the basic protocol, and multiple diverging basic protocol + dialects are most undesirable.
Signed-off-by: Markus Armbruster <armbru@redhat.com> --- v2: Clarify use of __RFQDN (Thanks, Luiz!) QMP/qmp-spec.txt | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 55 insertions(+), 0 deletions(-)