blk-mq: fill header with kernel-doc

Insert documentation for structs, enums and functions at header file.
Format existing and new comments at struct blk_mq_ops as
kernel-doc comments.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blk-mq.h

@@ -10,74 +10,171 @@ struct blk_mq_tags;
 struct blk_flush_queue;
 
 /**
- * struct blk_mq_hw_ctx - State for a hardware queue facing the hardware block device
+ * struct blk_mq_hw_ctx - State for a hardware queue facing the hardware
+ * block device
  */
 struct blk_mq_hw_ctx {
 	struct {
+		/** @lock: Protects the dispatch list. */
 		spinlock_t		lock;
+		/**
+		 * @dispatch: Used for requests that are ready to be
+		 * dispatched to the hardware but for some reason (e.g. lack of
+		 * resources) could not be sent to the hardware. As soon as the
+		 * driver can send new requests, requests at this list will
+		 * be sent first for a fairer dispatch.
+		 */
 		struct list_head	dispatch;
-		unsigned long		state;		/* BLK_MQ_S_* flags */
+		 /**
+		  * @state: BLK_MQ_S_* flags. Defines the state of the hw
+		  * queue (active, scheduled to restart, stopped).
+		  */
+		unsigned long		state;
 	} ____cacheline_aligned_in_smp;
 
+	/**
+	 * @run_work: Used for scheduling a hardware queue run at a later time.
+	 */
 	struct delayed_work	run_work;
+	/** @cpumask: Map of available CPUs where this hctx can run. */
 	cpumask_var_t		cpumask;
+	/**
+	 * @next_cpu: Used by blk_mq_hctx_next_cpu() for round-robin CPU
+	 * selection from @cpumask.
+	 */
 	int			next_cpu;
+	/**
+	 * @next_cpu_batch: Counter of how many works left in the batch before
+	 * changing to the next CPU.
+	 */
 	int			next_cpu_batch;
 
-	unsigned long		flags;		/* BLK_MQ_F_* flags */
+	/** @flags: BLK_MQ_F_* flags. Defines the behaviour of the queue. */
+	unsigned long		flags;
 
+	/**
+	 * @sched_data: Pointer owned by the IO scheduler attached to a request
+	 * queue. It's up to the IO scheduler how to use this pointer.
+	 */
 	void			*sched_data;
+	/**
+	 * @queue: Pointer to the request queue that owns this hardware context.
+	 */
 	struct request_queue	*queue;
+	/** @fq: Queue of requests that need to perform a flush operation. */
 	struct blk_flush_queue	*fq;
 
+	/**
+	 * @driver_data: Pointer to data owned by the block driver that created
+	 * this hctx
+	 */
 	void			*driver_data;
 
+	/**
+	 * @ctx_map: Bitmap for each software queue. If bit is on, there is a
+	 * pending request in that software queue.
+	 */
 	struct sbitmap		ctx_map;
 
+	/**
+	 * @dispatch_from: Software queue to be used when no scheduler was
+	 * selected.
+	 */
 	struct blk_mq_ctx	*dispatch_from;
+	/**
+	 * @dispatch_busy: Number used by blk_mq_update_dispatch_busy() to
+	 * decide if the hw_queue is busy using Exponential Weighted Moving
+	 * Average algorithm.
+	 */
 	unsigned int		dispatch_busy;
 
+	/** @type: HCTX_TYPE_* flags. Type of hardware queue. */
 	unsigned short		type;
+	/** @nr_ctx: Number of software queues. */
 	unsigned short		nr_ctx;
+	/** @ctxs: Array of software queues. */
 	struct blk_mq_ctx	**ctxs;
 
+	/** @dispatch_wait_lock: Lock for dispatch_wait queue. */
 	spinlock_t		dispatch_wait_lock;
+	/**
+	 * @dispatch_wait: Waitqueue to put requests when there is no tag
+	 * available at the moment, to wait for another try in the future.
+	 */
 	wait_queue_entry_t	dispatch_wait;
+
+	/**
+	 * @wait_index: Index of next available dispatch_wait queue to insert
+	 * requests.
+	 */
 	atomic_t		wait_index;
 
+	/**
+	 * @tags: Tags owned by the block driver. A tag at this set is only
+	 * assigned when a request is dispatched from a hardware queue.
+	 */
 	struct blk_mq_tags	*tags;
+	/**
+	 * @sched_tags: Tags owned by I/O scheduler. If there is an I/O
+	 * scheduler associated with a request queue, a tag is assigned when
+	 * that request is allocated. Else, this member is not used.
+	 */
 	struct blk_mq_tags	*sched_tags;
 
+	/** @queued: Number of queued requests. */
 	unsigned long		queued;
+	/** @run: Number of dispatched requests. */
 	unsigned long		run;
 #define BLK_MQ_MAX_DISPATCH_ORDER	7
+	/** @dispatched: Number of dispatch requests by queue. */
 	unsigned long		dispatched[BLK_MQ_MAX_DISPATCH_ORDER];
 
+	/** @numa_node: NUMA node the storage adapter has been connected to. */
 	unsigned int		numa_node;
+	/** @queue_num: Index of this hardware queue. */
 	unsigned int		queue_num;
 
+	/**
+	 * @nr_active: Number of active requests. Only used when a tag set is
+	 * shared across request queues.
+	 */
 	atomic_t		nr_active;
 
+	/** @cpuhp_dead: List to store request if some CPU die. */
 	struct hlist_node	cpuhp_dead;
+	/** @kobj: Kernel object for sysfs. */
 	struct kobject		kobj;
 
+	/** @poll_considered: Count times blk_poll() was called. */
 	unsigned long		poll_considered;
+	/** @poll_invoked: Count how many requests blk_poll() polled. */
 	unsigned long		poll_invoked;
+	/** @poll_success: Count how many polled requests were completed. */
 	unsigned long		poll_success;
 
 #ifdef CONFIG_BLK_DEBUG_FS
+	/**
+	 * @debugfs_dir: debugfs directory for this hardware queue. Named
+	 * as cpu<cpu_number>.
+	 */
 	struct dentry		*debugfs_dir;
+	/** @sched_debugfs_dir:	debugfs directory for the scheduler. */
 	struct dentry		*sched_debugfs_dir;
 #endif
 
+	/** @hctx_list:	List of all hardware queues. */
 	struct list_head	hctx_list;
 
-	/* Must be the last member - see also blk_mq_hw_ctx_size(). */
+	/**
+	 * @srcu: Sleepable RCU. Use as lock when type of the hardware queue is
+	 * blocking (BLK_MQ_F_BLOCKING). Must be the last member - see also
+	 * blk_mq_hw_ctx_size().
+	 */
 	struct srcu_struct	srcu[0];
 };
 
 /**
- * struct blk_mq_queue_map - ctx -> hctx mapping
+ * struct blk_mq_queue_map - Map software queues to hardware queues
  * @mq_map:       CPU ID to hardware queue index map. This is an array
  *	with nr_cpu_ids elements. Each element has a value in the range
  *	[@queue_offset, @queue_offset + @nr_queues).
@@ -92,10 +189,17 @@ struct blk_mq_queue_map {
 	unsigned int queue_offset;
 };
 
+/**
+ * enum hctx_type - Type of hardware queue
+ * @HCTX_TYPE_DEFAULT:	All I/O not otherwise accounted for.
+ * @HCTX_TYPE_READ:	Just for READ I/O.
+ * @HCTX_TYPE_POLL:	Polled I/O of any kind.
+ * @HCTX_MAX_TYPES:	Number of types of hctx.
+ */
 enum hctx_type {
-	HCTX_TYPE_DEFAULT,	/* all I/O not otherwise accounted for */
-	HCTX_TYPE_READ,		/* just for READ I/O */
-	HCTX_TYPE_POLL,		/* polled I/O of any kind */
+	HCTX_TYPE_DEFAULT,
+	HCTX_TYPE_READ,
+	HCTX_TYPE_POLL,
 
 	HCTX_MAX_TYPES,
 };
@@ -147,6 +251,12 @@ struct blk_mq_tag_set {
 	struct list_head	tag_list;
 };
 
+/**
+ * struct blk_mq_queue_data - Data about a request inserted in a queue
+ *
+ * @rq:   Request pointer.
+ * @last: If it is the last request in the queue.
+ */
 struct blk_mq_queue_data {
 	struct request *rq;
 	bool last;
@@ -174,81 +284,101 @@ typedef bool (busy_fn)(struct request_queue *);
 typedef void (complete_fn)(struct request *);
 typedef void (cleanup_rq_fn)(struct request *);
 
-
+/**
+ * struct blk_mq_ops - Callback functions that implements block driver
+ * behaviour.
+ */
 struct blk_mq_ops {
-	/*
-	 * Queue request
+	/**
+	 * @queue_rq: Queue a new request from block IO.
 	 */
 	queue_rq_fn		*queue_rq;
 
-	/*
-	 * If a driver uses bd->last to judge when to submit requests to
-	 * hardware, it must define this function. In case of errors that
-	 * make us stop issuing further requests, this hook serves the
+	/**
+	 * @commit_rqs: If a driver uses bd->last to judge when to submit
+	 * requests to hardware, it must define this function. In case of errors
+	 * that make us stop issuing further requests, this hook serves the
 	 * purpose of kicking the hardware (which the last request otherwise
 	 * would have done).
 	 */
 	commit_rqs_fn		*commit_rqs;
 
-	/*
-	 * Reserve budget before queue request, once .queue_rq is
+	/**
+	 * @get_budget: Reserve budget before queue request, once .queue_rq is
 	 * run, it is driver's responsibility to release the
 	 * reserved budget. Also we have to handle failure case
 	 * of .get_budget for avoiding I/O deadlock.
 	 */
 	get_budget_fn		*get_budget;
+	/**
+	 * @put_budget: Release the reserved budget.
+	 */
 	put_budget_fn		*put_budget;
 
-	/*
-	 * Called on request timeout
+	/**
+	 * @timeout: Called on request timeout.
 	 */
 	timeout_fn		*timeout;
 
-	/*
-	 * Called to poll for completion of a specific tag.
+	/**
+	 * @poll: Called to poll for completion of a specific tag.
 	 */
 	poll_fn			*poll;
 
+	/**
+	 * @complete: Mark the request as complete.
+	 */
 	complete_fn		*complete;
 
-	/*
-	 * Called when the block layer side of a hardware queue has been
-	 * set up, allowing the driver to allocate/init matching structures.
-	 * Ditto for exit/teardown.
+	/**
+	 * @init_hctx: Called when the block layer side of a hardware queue has
+	 * been set up, allowing the driver to allocate/init matching
+	 * structures.
 	 */
 	init_hctx_fn		*init_hctx;
+	/**
+	 * @exit_hctx: Ditto for exit/teardown.
+	 */
 	exit_hctx_fn		*exit_hctx;
 
-	/*
-	 * Called for every command allocated by the block layer to allow
-	 * the driver to set up driver specific data.
+	/**
+	 * @init_request: Called for every command allocated by the block layer
+	 * to allow the driver to set up driver specific data.
 	 *
 	 * Tag greater than or equal to queue_depth is for setting up
 	 * flush request.
-	 *
-	 * Ditto for exit/teardown.
 	 */
 	init_request_fn		*init_request;
+	/**
+	 * @exit_request: Ditto for exit/teardown.
+	 */
 	exit_request_fn		*exit_request;
-	/* Called from inside blk_get_request() */
+
+	/**
+	 * @initialize_rq_fn: Called from inside blk_get_request().
+	 */
 	void (*initialize_rq_fn)(struct request *rq);
 
-	/*
-	 * Called before freeing one request which isn't completed yet,
-	 * and usually for freeing the driver private data
+	/**
+	 * @cleanup_rq: Called before freeing one request which isn't completed
+	 * yet, and usually for freeing the driver private data.
 	 */
 	cleanup_rq_fn		*cleanup_rq;
 
-	/*
-	 * If set, returns whether or not this queue currently is busy
+	/**
+	 * @busy: If set, returns whether or not this queue currently is busy.
 	 */
 	busy_fn			*busy;
 
+	/**
+	 * @map_queues: This allows drivers specify their own queue mapping by
+	 * overriding the setup-time function that builds the mq_map.
+	 */
 	map_queues_fn		*map_queues;
 
 #ifdef CONFIG_BLK_DEBUG_FS
-	/*
-	 * Used by the debugfs implementation to show driver-specific
+	/**
+	 * @show_rq: Used by the debugfs implementation to show driver-specific
 	 * information about a request.
 	 */
 	void (*show_rq)(struct seq_file *m, struct request *rq);
@@ -391,14 +521,29 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q);
 
 unsigned int blk_mq_rq_cpu(struct request *rq);
 
-/*
+/**
+ * blk_mq_rq_from_pdu - cast a PDU to a request
+ * @pdu: the PDU (Protocol Data Unit) to be casted
+ *
+ * Return: request
+ *
  * Driver command data is immediately after the request. So subtract request
- * size to get back to the original request, add request size to get the PDU.
+ * size to get back to the original request.
  */
 static inline struct request *blk_mq_rq_from_pdu(void *pdu)
 {
 	return pdu - sizeof(struct request);
 }
+
+/**
+ * blk_mq_rq_to_pdu - cast a request to a PDU
+ * @rq: the request to be casted
+ *
+ * Return: pointer to the PDU
+ *
+ * Driver command data is immediately after the request. So add request to get
+ * the PDU.
+ */
 static inline void *blk_mq_rq_to_pdu(struct request *rq)
 {
 	return rq + 1;