text: /*-
   * Copyright (c) 2014-2016 MongoDB, Inc.
   * Copyright (c) 2008-2014 WiredTiger, Inc.
   *	All rights reserved.
   *
   * See the file LICENSE for redistribution information.
   */
  
  #include "wt_internal.h"
  
  /*
   * __wt_block_map --
   *	Map a segment of the file in, if possible.
   */
  int
  __wt_block_map(WT_SESSION_IMPL *session, WT_BLOCK *block,
      void *mapped_regionp, size_t *lengthp, void *mapped_cookiep)
  {
  	WT_DECL_RET;
  	WT_FILE_HANDLE *handle;
  
  	*(void **)mapped_regionp = NULL;
  	*lengthp = 0;
  	*(void **)mapped_cookiep = NULL;
  
  	/* Map support is configurable. */
  	if (!S2C(session)->mmap)
  		return (0);
  
  	/*
  	 * Turn off mapping when verifying the file, because we can't perform
  	 * checksum validation of mapped segments, and verify has to checksum
  	 * pages.
  	 */
  	if (block->verify)
  		return (0);
  
  	/*
  	 * Turn off mapping if the application configured a cache size maximum,
  	 * we can't control how much of the cache size we use in that case.
  	 */
  	if (block->os_cache_max != 0)
  		return (0);
  
  	/*
  	 * There may be no underlying functionality.
  	 */
  	handle = block->fh->handle;
  	if (handle->fh_map == NULL)
  		return (0);
  
  	/*
  	 * Map the file into memory.
  	 * Ignore not-supported errors, we'll read the file through the cache
  	 * if map fails.
  	 */
  	ret = handle->fh_map(handle,
  	    (WT_SESSION *)session, mapped_regionp, lengthp, mapped_cookiep);
  	if (ret == EBUSY || ret == ENOTSUP) {
  		*(void **)mapped_regionp = NULL;
  		ret = 0;
  	}
  
  	return (ret);
  }
  
  /*
   * __wt_block_unmap --
   *	Unmap any mapped-in segment of the file.
   */
  int
  __wt_block_unmap(WT_SESSION_IMPL *session,
      WT_BLOCK *block, void *mapped_region, size_t length, void *mapped_cookie)
  {
  	WT_FILE_HANDLE *handle;
  
  	/* Unmap the file from memory. */
  	handle = block->fh->handle;
  	return (handle->fh_unmap(handle,
  	    (WT_SESSION *)session, mapped_region, length, mapped_cookie));
  }
  