/*
   * zpool memory storage api
   *
   * Copyright (C) 2014 Dan Streetman
   *
   * This is a common frontend for memory storage pool implementations.
   * Typically, this is used to store compressed memory.
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/list.h>
  #include <linux/types.h>
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/module.h>
  #include <linux/zpool.h>
  
  struct zpool {

  	struct zpool_driver *driver;
  	void *pool;

  	const struct zpool_ops *ops;

  
  	struct list_head list;
  };
  
  static LIST_HEAD(drivers_head);
  static DEFINE_SPINLOCK(drivers_lock);
  
  static LIST_HEAD(pools_head);
  static DEFINE_SPINLOCK(pools_lock);
  
  /**
   * zpool_register_driver() - register a zpool implementation.
   * @driver:	driver to register
   */
  void zpool_register_driver(struct zpool_driver *driver)
  {
  	spin_lock(&drivers_lock);
  	atomic_set(&driver->refcount, 0);
  	list_add(&driver->list, &drivers_head);
  	spin_unlock(&drivers_lock);
  }
  EXPORT_SYMBOL(zpool_register_driver);
  
  /**
   * zpool_unregister_driver() - unregister a zpool implementation.
   * @driver:	driver to unregister.
   *
   * Module usage counting is used to prevent using a driver
   * while/after unloading, so if this is called from module
   * exit function, this should never fail; if called from
   * other than the module exit function, and this returns
   * failure, the driver is in use and must remain available.
   */
  int zpool_unregister_driver(struct zpool_driver *driver)
  {
  	int ret = 0, refcount;
  
  	spin_lock(&drivers_lock);
  	refcount = atomic_read(&driver->refcount);
  	WARN_ON(refcount < 0);
  	if (refcount > 0)
  		ret = -EBUSY;
  	else
  		list_del(&driver->list);
  	spin_unlock(&drivers_lock);
  
  	return ret;
  }
  EXPORT_SYMBOL(zpool_unregister_driver);

  /* this assumes @type is null-terminated. */

  static struct zpool_driver *zpool_get_driver(const char *type)

  {
  	struct zpool_driver *driver;
  
  	spin_lock(&drivers_lock);
  	list_for_each_entry(driver, &drivers_head, list) {
  		if (!strcmp(driver->type, type)) {
  			bool got = try_module_get(driver->owner);
  
  			if (got)
  				atomic_inc(&driver->refcount);
  			spin_unlock(&drivers_lock);
  			return got ? driver : NULL;
  		}
  	}
  
  	spin_unlock(&drivers_lock);
  	return NULL;
  }
  
  static void zpool_put_driver(struct zpool_driver *driver)
  {
  	atomic_dec(&driver->refcount);
  	module_put(driver->owner);
  }
  
  /**

   * zpool_has_pool() - Check if the pool driver is available
   * @type	The type of the zpool to check (e.g. zbud, zsmalloc)
   *
   * This checks if the @type pool driver is available.  This will try to load
   * the requested module, if needed, but there is no guarantee the module will
   * still be loaded and available immediately after calling.  If this returns
   * true, the caller should assume the pool is available, but must be prepared
   * to handle the @zpool_create_pool() returning failure.  However if this
   * returns false, the caller should assume the requested pool type is not
   * available; either the requested pool type module does not exist, or could
   * not be loaded, and calling @zpool_create_pool() with the pool type will
   * fail.
   *

   * The @type string must be null-terminated.
   *

   * Returns: true if @type pool is available, false if not
   */
  bool zpool_has_pool(char *type)
  {
  	struct zpool_driver *driver = zpool_get_driver(type);
  
  	if (!driver) {
  		request_module("zpool-%s", type);
  		driver = zpool_get_driver(type);
  	}
  
  	if (!driver)
  		return false;
  
  	zpool_put_driver(driver);
  	return true;
  }
  EXPORT_SYMBOL(zpool_has_pool);
  
  /**

   * zpool_create_pool() - Create a new zpool
   * @type	The type of the zpool to create (e.g. zbud, zsmalloc)

   * @name	The name of the zpool (e.g. zram0, zswap)

   * @gfp		The GFP flags to use when allocating the pool.
   * @ops		The optional ops callback.
   *
   * This creates a new zpool of the specified type.  The gfp flags will be
   * used when allocating memory, if the implementation supports it.  If the
   * ops param is NULL, then the created zpool will not be shrinkable.
   *
   * Implementations must guarantee this to be thread-safe.
   *

   * The @type and @name strings must be null-terminated.
   *

   * Returns: New zpool on success, NULL on failure.
   */

  struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,

  		const struct zpool_ops *ops)

  {
  	struct zpool_driver *driver;
  	struct zpool *zpool;

  	pr_debug("creating pool type %s
  ", type);

  
  	driver = zpool_get_driver(type);
  
  	if (!driver) {

  		request_module("zpool-%s", type);

  		driver = zpool_get_driver(type);
  	}
  
  	if (!driver) {
  		pr_err("no driver for type %s
  ", type);
  		return NULL;
  	}
  
  	zpool = kmalloc(sizeof(*zpool), gfp);
  	if (!zpool) {
  		pr_err("couldn't create zpool - out of memory
  ");
  		zpool_put_driver(driver);
  		return NULL;
  	}

  	zpool->driver = driver;

  	zpool->pool = driver->create(name, gfp, ops, zpool);

  	zpool->ops = ops;
  
  	if (!zpool->pool) {
  		pr_err("couldn't create %s pool
  ", type);
  		zpool_put_driver(driver);
  		kfree(zpool);
  		return NULL;
  	}

  	pr_debug("created pool type %s
  ", type);

  
  	spin_lock(&pools_lock);
  	list_add(&zpool->list, &pools_head);
  	spin_unlock(&pools_lock);
  
  	return zpool;
  }
  
  /**
   * zpool_destroy_pool() - Destroy a zpool
   * @pool	The zpool to destroy.
   *
   * Implementations must guarantee this to be thread-safe,
   * however only when destroying different pools.  The same
   * pool should only be destroyed once, and should not be used
   * after it is destroyed.
   *
   * This destroys an existing zpool.  The zpool should not be in use.
   */
  void zpool_destroy_pool(struct zpool *zpool)
  {

  	pr_debug("destroying pool type %s
  ", zpool->driver->type);

  
  	spin_lock(&pools_lock);
  	list_del(&zpool->list);
  	spin_unlock(&pools_lock);
  	zpool->driver->destroy(zpool->pool);
  	zpool_put_driver(zpool->driver);
  	kfree(zpool);
  }
  
  /**
   * zpool_get_type() - Get the type of the zpool
   * @pool	The zpool to check
   *
   * This returns the type of the pool.
   *
   * Implementations must guarantee this to be thread-safe.
   *
   * Returns: The type of zpool.
   */

  const char *zpool_get_type(struct zpool *zpool)

  {

  	return zpool->driver->type;

  }
  
  /**
   * zpool_malloc() - Allocate memory
   * @pool	The zpool to allocate from.
   * @size	The amount of memory to allocate.
   * @gfp		The GFP flags to use when allocating memory.
   * @handle	Pointer to the handle to set
   *
   * This allocates the requested amount of memory from the pool.
   * The gfp flags will be used when allocating memory, if the
   * implementation supports it.  The provided @handle will be
   * set to the allocated object handle.
   *
   * Implementations must guarantee this to be thread-safe.
   *
   * Returns: 0 on success, negative value on error.
   */
  int zpool_malloc(struct zpool *zpool, size_t size, gfp_t gfp,
  			unsigned long *handle)
  {
  	return zpool->driver->malloc(zpool->pool, size, gfp, handle);
  }
  
  /**
   * zpool_free() - Free previously allocated memory
   * @pool	The zpool that allocated the memory.
   * @handle	The handle to the memory to free.
   *
   * This frees previously allocated memory.  This does not guarantee
   * that the pool will actually free memory, only that the memory
   * in the pool will become available for use by the pool.
   *
   * Implementations must guarantee this to be thread-safe,
   * however only when freeing different handles.  The same
   * handle should only be freed once, and should not be used
   * after freeing.
   */
  void zpool_free(struct zpool *zpool, unsigned long handle)
  {
  	zpool->driver->free(zpool->pool, handle);
  }
  
  /**
   * zpool_shrink() - Shrink the pool size
   * @pool	The zpool to shrink.
   * @pages	The number of pages to shrink the pool.
   * @reclaimed	The number of pages successfully evicted.
   *
   * This attempts to shrink the actual memory size of the pool
   * by evicting currently used handle(s).  If the pool was
   * created with no zpool_ops, or the evict call fails for any
   * of the handles, this will fail.  If non-NULL, the @reclaimed
   * parameter will be set to the number of pages reclaimed,
   * which may be more than the number of pages requested.
   *
   * Implementations must guarantee this to be thread-safe.
   *
   * Returns: 0 on success, negative value on error/failure.
   */
  int zpool_shrink(struct zpool *zpool, unsigned int pages,
  			unsigned int *reclaimed)
  {
  	return zpool->driver->shrink(zpool->pool, pages, reclaimed);
  }
  
  /**
   * zpool_map_handle() - Map a previously allocated handle into memory
   * @pool	The zpool that the handle was allocated from
   * @handle	The handle to map
   * @mm		How the memory should be mapped
   *
   * This maps a previously allocated handle into memory.  The @mm
   * param indicates to the implementation how the memory will be
   * used, i.e. read-only, write-only, read-write.  If the
   * implementation does not support it, the memory will be treated
   * as read-write.
   *
   * This may hold locks, disable interrupts, and/or preemption,
   * and the zpool_unmap_handle() must be called to undo those
   * actions.  The code that uses the mapped handle should complete
   * its operatons on the mapped handle memory quickly and unmap
   * as soon as possible.  As the implementation may use per-cpu
   * data, multiple handles should not be mapped concurrently on
   * any cpu.
   *
   * Returns: A pointer to the handle's mapped memory area.
   */
  void *zpool_map_handle(struct zpool *zpool, unsigned long handle,
  			enum zpool_mapmode mapmode)
  {
  	return zpool->driver->map(zpool->pool, handle, mapmode);
  }
  
  /**
   * zpool_unmap_handle() - Unmap a previously mapped handle
   * @pool	The zpool that the handle was allocated from
   * @handle	The handle to unmap
   *
   * This unmaps a previously mapped handle.  Any locks or other
   * actions that the implementation took in zpool_map_handle()
   * will be undone here.  The memory area returned from
   * zpool_map_handle() should no longer be used after this.
   */
  void zpool_unmap_handle(struct zpool *zpool, unsigned long handle)
  {
  	zpool->driver->unmap(zpool->pool, handle);
  }
  
  /**
   * zpool_get_total_size() - The total size of the pool
   * @pool	The zpool to check
   *
   * This returns the total size in bytes of the pool.
   *
   * Returns: Total size of the zpool in bytes.
   */
  u64 zpool_get_total_size(struct zpool *zpool)
  {
  	return zpool->driver->total_size(zpool->pool);
  }

  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Dan Streetman <ddstreet@ieee.org>");
  MODULE_DESCRIPTION("Common API for compressed memory storage");