include/io_channel.h: add comments for public APIs

Change-Id: I85dfac522eb77e5d53fb2fc9c5bb8a75463f1480
Signed-off-by: Yanbo Zhou <yanbo.zhou@intel.com>
Reviewed-on: https://review.gerrithub.io/392919
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

include/spdk/io_channel.h

@@ -94,16 +94,19 @@ struct spdk_io_channel {
 };
 
 /**
- * \brief Initializes the calling thread for I/O channel allocation.
+ * Initializes the calling thread for I/O channel allocation.
  *
- * @param fn A function that may be called from any thread and is
+ * \param msg_fn A function that may be called from any thread and is passed a function
- *          passed a function pointer (spdk_thread_fn) that must be
+ * pointer (spdk_thread_fn) that must be called on the same thread that spdk_allocate_thread
- *          called on the same thread that spdk_allocate_thread
+ * was called from.
- *          was called from.
+ * \param start_poller_fn Function to be called to start a poller for the thread.
- * @param thread_ctx Context that will be passed to fn.
+ * \param stop_poller_fn Function to be called to stop a poller for the thread.
- * @param name Human-readable name for the thread; can be retrieved with spdk_thread_get_name().
+ * \param thread_ctx Context that will be passed to fn, start_poller_fn and spdk_stop_poller.
- *             The string is copied, so the pointed-to data only needs to be valid during the
+ * \param name Human-readable name for the thread; can be retrieved with spdk_thread_get_name().
- *             spdk_allocate_thread() call.  May be NULL to specify no name.
+ * The string is copied, so the pointed-to data only needs to be valid during the
+ * spdk_allocate_thread() call. May be NULL to specify no name.
+ *
+ * \return a pointer to the allocated thread on success or NULL on failure..
  */
 struct spdk_thread *spdk_allocate_thread(spdk_thread_pass_msg msg_fn,
 		spdk_start_poller start_poller_fn,
@@ -112,114 +115,146 @@ struct spdk_thread *spdk_allocate_thread(spdk_thread_pass_msg msg_fn,
 		const char *name);
 
 /**
- * \brief Releases any resources related to the calling thread for I/O channel allocation.
+ * Release any resources related to the calling thread for I/O channel allocation.
  *
  * All I/O channel references related to the calling thread must be released using
- *  spdk_put_io_channel() prior to calling this function.
+ * spdk_put_io_channel() prior to calling this function.
  */
 void spdk_free_thread(void);
 
 /**
- * \brief Get a handle to the current thread. This handle may be passed
+ * Get a handle to the current thread.
- * to other threads and used as the target of spdk_thread_send_msg().
+ *
+ * This handle may be passed to other threads and used as the target of
+ * spdk_thread_send_msg().
  *
  * \sa spdk_io_channel_get_thread()
+ *
+ * \return a pointer to the current thread on success or NULL on failure.
  */
 struct spdk_thread *spdk_get_thread(void);
 
 /**
- * \brief Get a thread's name.
+ * Get a thread's name.
+ *
+ * \param thread Thread to query.
+ *
+ * \return the name of the thread.
  */
 const char *spdk_thread_get_name(const struct spdk_thread *thread);
 
 /**
- * \brief Send a message to the given thread. The message
+ * Send a message to the given thread.
- * may be sent asynchronously - i.e. spdk_thread_send_msg
- * may return prior to `fn` being called.
  *
- * @param thread The target thread.
+ * The message may be sent asynchronously - i.e. spdk_thread_send_msg may return
- * @param fn This function will be called on the given thread.
+ * prior to `fn` being called.
- * @param ctx This context will be passed to fn when called.
+ *
+ * \param thread The target thread.
+ * \param fn This function will be called on the given thread.
+ * \param ctx This context will be passed to fn when called.
  */
 void spdk_thread_send_msg(const struct spdk_thread *thread, spdk_thread_fn fn, void *ctx);
 
 /**
- * \brief Send a message to each thread, serially. The message
+ * Send a message to each thread, serially.
- * is sent asynchronously - i.e. spdk_for_each_thread
- * will return prior to `fn` being called on each thread.
  *
- * @param fn This is the function that will be called on each thread.
+ * The message is sent asynchronously - i.e. spdk_for_each_thread will return
- * @param ctx This context will be passed to fn when called.
+ * prior to `fn` being called on each thread.
- * @param cpl This will be called on the originating thread after `fn` has been
+ *
- *            called on each thread.
+ * \param fn This is the function that will be called on each thread.
+ * \param ctx This context will be passed to fn when called.
+ * \param cpl This will be called on the originating thread after `fn` has been
+ * called on each thread.
  */
 void spdk_for_each_thread(spdk_thread_fn fn, void *ctx, spdk_thread_fn cpl);
 
 /**
- * \brief Register a poller on the current thread. The poller can be
+ * Register a poller on the current thread.
- * unregistered by calling spdk_poller_unregister().
  *
- * @param fn This function will be called every `period_microseconds`
+ * The poller can be unregistered by calling spdk_poller_unregister().
- * @param arg Passed to fn
+ *
- * @param period_microseconds How often to call `fn`. If 0, call `fn` as often as possible.
+ * \param fn This function will be called every `period_microseconds`.
+ * \param arg Argument passed to fn.
+ * \param period_microseconds How often to call `fn`. If 0, call `fn` as often
+ *  as possible.
+ *
+ * \return a pointer to the poller registered on the current thread on success
+ * or NULL on failure.
  */
 struct spdk_poller *spdk_poller_register(spdk_thread_fn fn,
 		void *arg,
 		uint64_t period_microseconds);
 
 /**
- * \brief Unregister a poller on the current thread.
+ * Unregister a poller on the current thread.
  *
- * @param ppoller The poller to unregister.
+ * \param ppoller The poller to unregister.
  */
 void spdk_poller_unregister(struct spdk_poller **ppoller);
 
 /**
- * \brief Register the opaque io_device context as an I/O device.
+ * Register the opaque io_device context as an I/O device.
  *
  * After an I/O device is registered, it can return I/O channels using the
- *  spdk_get_io_channel() function.  create_cb is the callback function invoked
+ * spdk_get_io_channel() function.
- *  to allocate any resources required for a new I/O channel.  destroy_cb is the
+ *
- *  callback function invoked to release the resources for an I/O channel.  ctx_size
+ * \param io_device The pointer to io_device context.
- *  is the size of the context buffer allocated to store references to allocated I/O
+ * \param create_cb Callback function invoked to allocate any resources required
- *  channel resources.
+ * for a new I/O channel.
+ * \param destroy_cb Callback function invoked to release the resources for an
+ * I/O channel.
+ * \param ctx_size The size of the context buffer allocated to store references
+ * to allocated I/O channel resources.
  */
 void spdk_io_device_register(void *io_device, spdk_io_channel_create_cb create_cb,
 			     spdk_io_channel_destroy_cb destroy_cb, uint32_t ctx_size);
 
 /**
- * \brief Unregister the opaque io_device context as an I/O device.
+ * Unregister the opaque io_device context as an I/O device.
  *
- * The actual unregistration might be deferred until all active I/O channels are destroyed.
+ * The actual unregistration might be deferred until all active I/O channels are
- *  unregister_cb is an optional callback function invoked to release any references to
+ * destroyed.
- *  this I/O device.
+ *
+ * \param io_device The pointer to io_device context.
+ * \param unregister_cb An optional callback function invoked to release any
+ * references to this I/O device.
  */
 void spdk_io_device_unregister(void *io_device, spdk_io_device_unregister_cb unregister_cb);
 
 /**
- * \brief Gets an I/O channel for the specified io_device to be used by the calling thread.
+ * Get an I/O channel for the specified io_device to be used by the calling thread.
  *
- * The io_device context pointer specified must have previously been registered using
+ * The io_device context pointer specified must have previously been registered
- *  spdk_io_device_register().  If an existing I/O channel does not exist yet for the given
+ * using spdk_io_device_register(). If an existing I/O channel does not exist
- *  io_device on the calling thread, it will allocate an I/O channel and invoke the create_cb
+ * yet for the given io_device on the calling thread, it will allocate an I/O
- *  function pointer specified in spdk_io_device_register().  If an I/O channel already
+ * channel and invoke the create_cb function pointer specified in spdk_io_device_register().
- *  exists for the given io_device on the calling thread, its reference is returned rather
+ * If an I/O channel already exists for the given io_device on the calling thread,
- *  than creating a new I/O channel.
+ * its reference is returned rather than creating a new I/O channel.
+ *
+ * \param io_device The pointer to io_device context.
+ *
+ * \return a pointer to the I/O channel for this device on success or NULL on failure.
  */
 struct spdk_io_channel *spdk_get_io_channel(void *io_device);
 
 /**
- * \brief Releases a reference to an I/O channel. This happens asynchronously.
+ * Release a reference to an I/O channel. This happens asynchronously.
  *
- * Actual release will happen on the same thread that called spdk_get_io_channel() for the
+ * Actual release will happen on the same thread that called spdk_get_io_channel()
- *  specified I/O channel.  If this releases the last reference to the I/O channel, The
+ * for the specified I/O channel. If this releases the last reference to the
- *  destroy_cb function specified in spdk_io_device_register() will be invoked to release
+ * I/O channel, The destroy_cb function specified in spdk_io_device_register()
- *  any associated resources.
+ * will be invoked to release any associated resources.
+ *
+ * \param ch I/O channel to release a reference.
  */
 void spdk_put_io_channel(struct spdk_io_channel *ch);
 
 /**
- * \brief Returns the context buffer associated with an I/O channel.
+ * Get the context buffer associated with an I/O channel.
+ *
+ * \param ch I/O channel.
+ *
+ * \return a pointer to the context buffer.
  */
 static inline void *
 spdk_io_channel_get_ctx(struct spdk_io_channel *ch)
@@ -228,36 +263,75 @@ spdk_io_channel_get_ctx(struct spdk_io_channel *ch)
 }
 
 /**
- *  \brief Returns an I/O channel from a context buffer. This is
+ * Get I/O channel from the context buffer. This is the inverse of
- * the inverse of spdk_io_channel_get_ctx().
+ * spdk_io_channel_get_ctx().
+ *
+ * \param ctx The pointer to the context buffer.
+ *
+ * \return a pointer to the I/O channel associated with the context buffer.
  */
 struct spdk_io_channel *spdk_io_channel_from_ctx(void *ctx);
 
 /**
- * \brief Returns the spdk_thread associated with an I/O channel.
+ * Get the thread associated with an I/O channel.
+ *
+ * \param ch I/O channel.
+ *
+ * \return a pointer to the thread associated with the I/O channel
  */
 struct spdk_thread *spdk_io_channel_get_thread(struct spdk_io_channel *ch);
 
 /**
- * \brief Call 'fn' on each channel associated with io_device. This happens
+ * Call 'fn' on each channel associated with io_device.
- * asynchronously, so fn may be called after spdk_for_each_channel returns.
+ *
- * 'fn' will be called on the correct thread for each channel. 'fn' will be
+ * This happens asynchronously, so fn may be called after spdk_for_each_channel
- * called for each channel serially, such that two calls to 'fn' will not
+ * returns. 'fn' will be called for each channel serially, such that two calls
- * overlap in time. After 'fn' has been called, call
+ * to 'fn' will not overlap in time. After 'fn' has been called, call
  * spdk_for_each_channel_continue() to continue iterating.
  *
- * Once 'fn' has been called on each channel, 'cpl' will be called
+ * \param io_device 'fn' will be called on each channel associated with this io_device.
- * on the thread that spdk_for_each_channel was initially called from.
+ * \param fn Called on the appropriate thread for each channel associated with io_device.
+ * \param ctx Context buffer registered to spdk_io_channel_iter that can be obatined
+ * form the function spdk_io_channel_iter_get_ctx().
+ * \param cpl Called on the thread that spdk_for_each_channel was initially called
+ * from when 'fn' has been called on each channel.
  */
 void spdk_for_each_channel(void *io_device, spdk_channel_msg fn, void *ctx,
 			   spdk_channel_for_each_cpl cpl);
 
+/**
+ * Get io_device from the I/O channel iterator.
+ *
+ * \param i I/O channel iterator.
+ *
+ * \return a pointer to the io_device.
+ */
 void *spdk_io_channel_iter_get_io_device(struct spdk_io_channel_iter *i);
 
+/**
+ * Get I/O channel from the I/O channel iterator.
+ *
+ * \param i I/O channel iterator.
+ *
+ * \return a pointer to the I/O channel.
+ */
 struct spdk_io_channel *spdk_io_channel_iter_get_channel(struct spdk_io_channel_iter *i);
 
+/**
+ * Get context buffer from the I/O channel iterator.
+ *
+ * \param i I/O channel iterator.
+ *
+ * \return a pointer to the context buffer.
+ */
 void *spdk_io_channel_iter_get_ctx(struct spdk_io_channel_iter *i);
 
+/**
+ * Helper function to iterate all channels for spdk_for_each_channel().
+ *
+ * \param i I/O channel iterator.
+ * \param status Status for the I/O channel iterator.
+ */
 void spdk_for_each_channel_continue(struct spdk_io_channel_iter *i, int status);
 
 #ifdef __cplusplus