Add cache locking functions in trylock variant

- Add cache trylock and read trylock functions.
- Introduce new error code -OCF_ERR_NO_LOCK.
- Change trylock functions in env to return this code in case of
  lock contention.

[ENV CHANGES REQUIRED]
Following functions should return 0 on success or -OCF_ERR_NO_LOCK
in case of lock contention:
- env_mutex_trylock()
- env_rwsem_up_read_trylock()
- env_rwsem_up_write_trylock()

Signed-off-by: Robert Baldyga <robert.baldyga@intel.com>

inc/ocf_err.h

@@ -18,21 +18,24 @@ typedef enum {
 	/** Invalid input parameter value */
 	OCF_ERR_INVAL = 1000000,
 
-	/** Invalid volume type */
-	OCF_ERR_INVAL_VOLUME_TYPE,
-
 	/** Operation interrupted */
 	OCF_ERR_INTR,
 
+	/** Out of memory */
+	OCF_ERR_NO_MEM,
+
+	/** Lock not acquired */
+	OCF_ERR_NO_LOCK,
+
+	/** Invalid volume type */
+	OCF_ERR_INVAL_VOLUME_TYPE,
+
 	/** Unknown error occurred */
 	OCF_ERR_UNKNOWN,
 
 	/*!< To many caches */
 	OCF_ERR_TOO_MANY_CACHES,
 
-	/** Out of memory */
-	OCF_ERR_NO_MEM,
-
 	/** Not enough RAM to start cache */
 	OCF_ERR_NO_FREE_RAM,
 

inc/ocf_mngt.h

@@ -124,6 +124,34 @@ int ocf_mngt_cache_lock(ocf_cache_t cache);
  */
 int ocf_mngt_cache_read_lock(ocf_cache_t cache);
 
+/**
+ * @brief Lock cache for management oparations (write lock, exclusive)
+ *
+ * @param[in] cache Handle to cache
+ *
+ * @retval 0 Cache successfully locked
+ * @retval -OCF_ERR_CACHE_NOT_EXIST Can not lock cache - cache is already
+ *					stopping
+ * @retval -OCF_ERR_CACHE_IN_USE Can not lock cache - cache is in use
+ * @retval -OCF_ERR_NO_LOCK Lock not acquired
+ */
+int ocf_mngt_cache_trylock(ocf_cache_t cache);
+
+/**
+ * @brief Lock cache for read - assures cache config does not change while
+ *		lock is being held, while allowing other users to acquire
+ *		read lock in parallel.
+ *
+ * @param[in] cache Handle to cache
+ *
+ * @retval 0 Cache successfully locked
+ * @retval -OCF_ERR_CACHE_NOT_EXIST Can not lock cache - cache is already
+ *					stopping
+ * @retval -OCF_ERR_CACHE_IN_USE Can not lock cache - cache is in use
+ * @retval -OCF_ERR_NO_LOCK Lock not acquired
+ */
+int ocf_mngt_cache_read_trylock(ocf_cache_t cache);
+
 /**
  * @brief Write-unlock cache
  *