The Linux Kernel API | ||
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The &request_queue_t to be initialised
The function to be called to process requests that have been placed on the queue.
If a block device wishes to use the standard request handling procedures, which sorts requests and coalesces adjacent requests, then it must call blk_init_queue. The function rfn will be called when there are requests on the queue that need to be processed. If the device supports plugging, then rfn may not be called immediately when requests are available on the queue, but may be called at some time later instead. Plugged queues are generally unplugged when a buffer belonging to one of the requests on the queue is needed, or due to memory pressure.
rfn is not required, or even expected, to remove all requests off the queue, but only as many as it can handle at a time. If it does leave requests on the queue, it is responsible for arranging that the requests get dealt with eventually.
A global spin lock $io_request_lock must be held while manipulating the requests on the request queue.
The request on the head of the queue is by default assumed to be potentially active, and it is not considered for re-ordering or merging whenever the given queue is unplugged. This behaviour can be changed with blk_queue_headactive.
blk_init_queue must be paired with a blk_cleanup_queue call when the block device is deactivated (such as at module unload).
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