[Xcb] new "length" element needs a type?

Uli Schlachter psychon at znc.in
Mon Sep 20 14:21:25 UTC 2021


Am 20.09.21 um 16:12 schrieb Tycho Andersen:
> On Mon, Sep 20, 2021 at 04:05:11PM +0200, Uli Schlachter wrote:
>> Am 19.09.21 um 15:34 schrieb Tycho Andersen:
>>> There is a new length element for structs documented in c36dde3f4535
>>> ("Add element to specify expression that defines length of a struct")
>>> with a first use introduced in f0db8b7d31a3 ("xinput: Add length
>>> specification for DeviceClass struct"), but as near as I can tell
>>> there's no type information for this, either in the docs or in this
>>> particular usage.
>> Why does there need to be a type? Other uses of expressions in the XML
>> are also untyped.
>> For example:
>>   <struct name="SetupAuthenticate">
>>     <field type="CARD8" name="status" /> <!-- always 2 -> Authenticate -->
>>     <pad bytes="5" />
>>     <field type="CARD16" name="length" />
>>     <list type="char" name="reason">
>>       <op op="*">
>>         <fieldref>length</fieldref>
>>         <value>4</value>
>>       </op>
>>     </list>
>>   </struct>
>> Here, the length of the list is 4*length and there is again no explicit
>> type given for the length.
> Huh? The length field has type="CARD16" doesn't it?
> The list itself as type="char". Which thing here doesn't have an
> explicit type?

Nothing. So perhaps I am misunderstanding you.

What does not have an explicit type with the new <length> element? The
field "len" has type="CARD16", doesn't it? Put differently: What is the
difference to SetupAuthenticate above?

    <struct name="DeviceClass">
            <op op="*">
        <field type="CARD16"   name="type" enum="DeviceClassType" />
        <field type="CARD16"   name="len" />

- He wants the impossible...!
- That's the short definition of 'captain'.

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