iokit/IOKit/IOService.h

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.
200 For each category, the highest scoring driver in that category is attached to the provider, and its @link start start@/link method called. If <code>start</code> is successful, the rest of the drivers in the same match category are discarded, otherwise the next highest scoring driver is started, and so on.
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.
229 A string defining the driver category for matching purposes. All drivers with no <code>IOMatchCategory</code> property are considered to be in the same default category. Only one driver in a category can be started on each provider.
372     @param category An OSSymbol corresponding to an IOMatchCategory matching property.
373 	@result Returns a reference to the IOService child with the given category. The result should be released by the caller.
376     virtual IOService * copyClientWithCategory( const OSSymbol * category );
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.
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.
1245     IOService * getClientWithCategory( const OSSymbol * category )