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mr-liang2504
109 lines
6.4 KiB
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109 lines
6.4 KiB
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<div class="title">Compatibility and Behavior across kernel versions </div> </div>
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<div class="textblock"><p>This page describes libevdev's behavior when the build-time kernel and the run-time kernel differ in their feature set.</p>
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<p>With the exception of event names, libevdev defines features that may be missing on older kernels and building on such kernels will not disable features. Running libevdev on a kernel that is missing some feature will change libevdev's behavior. In most cases, the new behavior should be obvious, but it is spelled out below in detail.</p>
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<h1><a class="anchor" id="autotoc_md14"></a>
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Minimum requirements</h1>
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<p>libevdev requires a 2.6.36 kernel as minimum. Specifically, it requires kernel-support for <code>ABS_MT_SLOT</code>.</p>
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<h1><a class="anchor" id="autotoc_md15"></a>
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Event and input property names</h1>
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<p>Event names and input property names are defined at build-time by the linux/input.h shipped with libevdev. The list of event names is compiled at build-time, any events not defined at build time will not resolve. Specifically, <a class="el" href="group__misc.html#gab407b3c2caaae502859c28460cad17bb">libevdev_event_code_get_name()</a> for an undefined type or code will always return <code>NULL</code>. Likewise, <a class="el" href="group__misc.html#gacc12bdb7b912070ac9c375428f2c9892">libevdev_property_get_name()</a> will return NULL for properties undefined at build-time.</p>
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<h1><a class="anchor" id="autotoc_md16"></a>
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Input properties</h1>
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<p>If the kernel does not support input properties, specifically the <code>EVIOCGPROPS</code> ioctl, libevdev does not expose input properties to the caller. Specifically, <a class="el" href="group__bits.html#ga36d529ea53f4522004bc7d16c051464b">libevdev_has_property()</a> will always return 0 unless the property has been manually set with <a class="el" href="group__kernel.html#gafc552080520c9d886452b05f3a1d75b6">libevdev_enable_property()</a>.</p>
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<p>This also applies to the libevdev-uinput code. If uinput does not honor <code>UI_SET_PROPBIT</code>, libevdev will continue without setting the properties on the device.</p>
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<h1><a class="anchor" id="autotoc_md17"></a>
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MT slot behavior</h1>
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<p>If the kernel does not support the <code>EVIOCGMTSLOTS</code> ioctl, libevdev assumes all values in all slots are 0 and continues without an error.</p>
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<h1><a class="anchor" id="autotoc_md18"></a>
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SYN_DROPPED behavior</h1>
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<p>A kernel without <code>SYN_DROPPED</code> won't send such an event. <a class="el" href="group__events.html#gabb96c864e836c0b98788f4ab771c3a76" title="Get the next event from the device.">libevdev_next_event()</a> will never require the switch to sync mode. </p>
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