text: /*-
   *   BSD LICENSE
   *
   *   Copyright (c) Intel Corporation.
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   *   Redistribution and use in source and binary forms, with or without
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   *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  /** \file
   * IO channel
   */
  
  #ifndef SPDK_IO_CHANNEL_H_
  #define SPDK_IO_CHANNEL_H_
  
  #include "spdk/stdinc.h"
  
  #include "spdk/queue.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  struct spdk_thread;
  struct spdk_io_channel_iter;
  struct spdk_poller;
  
  /**
   * Callback function for a thread.
   *
   * \param ctx Context passed as arg to spdk_thread_pass_msg().
   */
  typedef void (*spdk_thread_fn)(void *ctx);
  
  /**
   * Function to be called to pass a message to a thread.
   *
   * \param fn Callback function for a thread.
   * \param ctx Context passed to fn.
   * \param thread_ctx Context for the thread.
   */
  typedef void (*spdk_thread_pass_msg)(spdk_thread_fn fn, void *ctx,
  				     void *thread_ctx);
  
  /**
   * Callback function for a poller.
   *
   * \param ctx Context passed as arg to spdk_poller_register().
   * \return 0 to indicate that polling took place but no events were found;
   * positive to indicate that polling took place and some events were processed;
   * negative if the poller does not provide spin-wait information.
   */
  typedef int (*spdk_poller_fn)(void *ctx);
  
  /**
   * Function to be called to start a poller for the thread.
   *
   * \param thread_ctx Context for the thread.
   * \param fn Callback function for a poller.
   * \param arg Argument passed to callback.
   * \param period Polling period in microseconds.
   *
   * \return a pointer to the poller on success, or NULL on failure.
   */
  typedef struct spdk_poller *(*spdk_start_poller)(void *thread_ctx,
  		spdk_poller_fn fn,
  		void *arg,
  		uint64_t period_microseconds);
  
  /**
   * Function to be called to stop a poller.
   *
   * \param poller Poller to stop.
   * \param thread_ctx Context for the thread.
   */
  typedef void (*spdk_stop_poller)(struct spdk_poller *poller, void *thread_ctx);
  
  /**
   * I/O channel creation callback.
   *
   * \param io_device I/O device associated with this channel.
   * \param ctx_buf Context for the I/O device.
   */
  typedef int (*spdk_io_channel_create_cb)(void *io_device, void *ctx_buf);
  
  /**
   * I/O channel destruction callback.
   *
   * \param io_device I/O device associated with this channel.
   * \param ctx_buf Context for the I/O device.
   */
  typedef void (*spdk_io_channel_destroy_cb)(void *io_device, void *ctx_buf);
  
  /**
   * I/O device unregister callback.
   *
   * \param io_device Unregistered I/O device.
   */
  typedef void (*spdk_io_device_unregister_cb)(void *io_device);
  
  /**
   * Called on the appropriate thread for each channel associated with io_device.
   *
   * \param i I/O channel iterator.
   */
  typedef void (*spdk_channel_msg)(struct spdk_io_channel_iter *i);
  
  /**
   * spdk_for_each_channel() callback.
   *
   * \param i I/O channel iterator.
   * \param status 0 if it completed successfully, or negative errno if it failed.
   */
  typedef void (*spdk_channel_for_each_cpl)(struct spdk_io_channel_iter *i, int status);
  
  /**
   * \brief Represents a per-thread channel for accessing an I/O device.
   *
   * An I/O device may be a physical entity (i.e. NVMe controller) or a software
   *  entity (i.e. a blobstore).
   *
   * This structure is not part of the API - all accesses should be done through
   *  spdk_io_channel function calls.
   */
  struct spdk_io_channel {
  	struct spdk_thread		*thread;
  	struct io_device		*dev;
  	uint32_t			ref;
  	TAILQ_ENTRY(spdk_io_channel)	tailq;
  	spdk_io_channel_destroy_cb	destroy_cb;
  
  	/*
  	 * Modules will allocate extra memory off the end of this structure
  	 *  to store references to hardware-specific references (i.e. NVMe queue
  	 *  pairs, or references to child device spdk_io_channels (i.e.
  	 *  virtual bdevs).
  	 */
  };
  
  /**
   * Initializes the calling thread for I/O channel allocation.
   *
   * \param msg_fn A function that may be called from any thread and is passed a function
   * pointer (spdk_thread_fn) that must be called on the same thread that spdk_allocate_thread
   * was called from.
   * \param start_poller_fn Function to be called to start a poller for the thread.
   * \param stop_poller_fn Function to be called to stop a poller for the thread.
   * \param thread_ctx Context that will be passed to fn, start_poller_fn and spdk_stop_poller.
   * \param name Human-readable name for the thread; can be retrieved with spdk_thread_get_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,
  		spdk_stop_poller stop_poller_fn,
  		void *thread_ctx,
  		const char *name);
  
  /**
   * 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.
   */
  void spdk_free_thread(void);
  
  /**
   * Get a handle to the current thread.
   *
   * 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);
  
  /**
   * 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);
  
  /**
   * Send a message to the given thread.
   *
   * The message may be sent asynchronously - i.e. spdk_thread_send_msg may return
   * prior to `fn` being 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);
  
  /**
   * Send a message to each thread, serially.
   *
   * The message 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.
   * \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);
  
  /**
   * Register a poller on the current thread.
   *
   * The poller can be unregistered by calling spdk_poller_unregister().
   *
   * \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_poller_fn fn,
  		void *arg,
  		uint64_t period_microseconds);
  
  /**
   * Unregister a poller on the current thread.
   *
   * \param ppoller The poller to unregister.
   */
  void spdk_poller_unregister(struct spdk_poller **ppoller);
  
  /**
   * 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.
   *
   * \param io_device The pointer to io_device context.
   * \param create_cb Callback function invoked to allocate any resources required
   * 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);
  
  /**
   * 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.
   *
   * \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);
  
  /**
   * 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 spdk_io_device_register(). If an existing I/O channel does not exist
   * yet for the given io_device on the calling thread, it will allocate an I/O
   * channel and invoke the create_cb function pointer specified in spdk_io_device_register().
   * If an I/O channel already exists for the given io_device on the calling thread,
   * 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);
  
  /**
   * 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 specified I/O channel. If this releases the last reference to the
   * I/O channel, The destroy_cb function specified in spdk_io_device_register()
   * 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);
  
  /**
   * 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)
  {
  	return (uint8_t *)ch + sizeof(*ch);
  }
  
  /**
   * Get I/O channel from the context buffer. This is the inverse of
   * 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);
  
  /**
   * 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);
  
  /**
   * Call 'fn' on each channel associated with io_device.
   *
   * This happens asynchronously, so fn may be called after spdk_for_each_channel
   * returns. 'fn' will be called for each channel serially, such that two calls
   * to 'fn' will not overlap in time. After 'fn' has been called, call
   * spdk_for_each_channel_continue() to continue iterating.
   *
   * \param io_device 'fn' will be called on each channel associated with this io_device.
   * \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
  }
  #endif
  
  #endif /* SPDK_IO_CHANNEL_H_ */
  