Vladimir Sementsov-Ogievskiy <[email protected]> writes:
> On 10.10.25 10:52, Michael Tokarev wrote:
>> On 10/9/25 17:17, Markus Armbruster wrote:
>>> Vladimir Sementsov-Ogievskiy <[email protected]> writes:
>>>
>>>> They were deprecated in 9.2, now we can remove them.
>>>> New options to use are reconnect-ms.
>> Speaking of the option itself.. I'd not remove it, instead,
>> I'd de-deprecate it, and allow units to be specified for it,
>> like reconnect=10ms (defaults to s). Or reconnect=0.1 (in
>> fractions of second). But it's just me, it looks like :)
>
> QAPI is not for humans) So simple milliseconds integer is better,
> then parse the variety of suffixes. And it better fit into json
> (number is number, not a string)
>
>> Also, `has_reconnect_ms` becomes redundant after applying this
>> patch, - it should be enough to use just reconnect_ms, which
>> defaults to 0. But this can be done in a subsequent cleanup.
>>
>
> You mean just use sock->reconnect_ms instead of explicit
>
> int64_t reconnect_ms = sock->has_reconnect_ms ? sock->reconnect_ms : 0;
>
> ?
We routinely exploit that QAPI initializes absent members to zero.
> I believe that QMP will zero-initialize everything. But I'm not sure
> that we do zero initialize this structure on all paths.. Keeping also in mind
> handling other fields here like
>
> bool is_telnet = sock->has_telnet ? sock->telnet : false;
> bool is_tn3270 = sock->has_tn3270 ? sock->tn3270 : false;
> bool is_waitconnect = sock->has_wait ? sock->wait : false;
> bool is_websock = sock->has_websocket ? sock->websocket : false;
>
> To drop this, we should check for all paths, that incoming structure is
> zero-initialized. And no guarantee that it does not break in future.
>
> Probably, we can implement a new QAPI feature "value with default to zero",
> so that we can avoid existence of .has_foo field at all for such fields.
> No field - no problem.. But not in this series)
The simple way to do "optional" is to have the machinery supply a
default value.
The less simple way is to add a distinct extra value that means
"absent". This permits "absent" to means something else than any value.
QAPI does the latter. Not my choice; I inherited it :)
For pointers, generated C uses null as distinct extra value. Works,
because "present" implies non-null.
For other types, generated C uses a pair of variables (has_FOO, FOO),
where
(true, V) means present with value V
(false, zero) means absent
(false, non-zero) is invalid
This results in slightly more complicated code.
Most of the time, code maps "absent" to a default value. This default
value is not visible in the schema, it's buried in the C code. When a
type gets used in multiple places, each place can pick its own default.
Bothersome to document, and the system cannot ensure the code matches
its documentation. Strong dislike.
Special case: when the default value is zero, we can ignore has_FOO and
just use FOO. See "routinely exploit" above.
We could extend the QAPI schema language to let us specify the default
value. The generator could then elide has_FOO. Code would become
simpler.
