iokit/IOKit/IOService.h

196 The driver class is instantiated and <code>init()</code> called with its property table. The new driver instance is then attached to the provider, and has its @link probe probe@/link method called with the provider as an argument. The default <code>probe</code> method does nothing but return success, but a driver may implement this method to interrogate the provider to make sure it can work with it. It may also modify its probe score at this time. After probe, the driver is detached and the next in the list is considered (ie. attached, probed, and detached).
198 When the probing phase is complete, the list consists of successfully probed drivers, in order of their probe score (after adjustment during the @link probe probe@/link call). The list is then divided into categories based on the <code>kIOMatchCategoryKey</code> property ("IOMatchCategory"); drivers without a match category are all considered in one default category. Match categories allow multiple clients of a provider to be attached and started, though the provider may also enforce open/close semantics to gain active access to it.
202 The driver should only consider itself in action when the start method is called, meaning it has been selected for use on the provider, and consuming that particular match category. It should also be prepared to be allocated, probed and freed even if the probe was successful.
223 The probe score initially used to order multiple matching drivers.
461 /*! @function probe
463     @discussion The registration process for an IOService object (the provider) includes instantiating possible driver clients. The <code>probe</code> method is called in the client instance to check the matched service can be used before the driver is considered to be started. Since matching screens many possible providers, in many cases the <code>probe</code> method can be left unimplemented by IOService subclasses. The client is already attached to the provider when <code>probe</code> is called.
465     @param score Pointer to the current driver's probe score, which is used to order multiple matching drivers in the same match category. It defaults to the value of the <code>IOProbeScore</code> property in the drivers property table, or <code>kIODefaultProbeScore</code> if none is specified. The <code>probe</code> method may alter the score to affect start order.
466     @result An IOService instance or zero when the probe is unsuccessful. In almost all cases the value of <code>this</code> is returned on success. If another IOService object is returned, the probed instance is detached and freed, and the returned instance is used in its stead for <code>start</code>. */
468     virtual IOService * probe(	IOService * 	provider,
473     @discussion The <code>start</code> method of an IOService instance is called by its provider when it has been selected (due to its probe score and match category) as the winning client. The client is already attached to the provider when <code>start</code> is called.<br>Implementations of <code>start</code> must call <code>start</code> on their superclass at an appropriate point. If an implementation of <code>start</code> has already called <code>super::start</code> but subsequently determines that it will fail, it must call <code>super::stop</code> to balance the prior call to <code>super::start</code> and prevent reference leaks.
621     @param score Pointer to the current driver's probe score, which is used to order multiple matching drivers in the same match category. It defaults to the value of the <code>IOProbeScore</code> property in the drivers property table, or <code>kIODefaultProbeScore</code> if none is specified.