* Extracted file_map API out of the file cache - it's now an optional service

that can be used by file systems.
* Changed the way the file cache works: instead of reading/writing to the
  underlying device directly, it can now be used for any data source, ie.
  also network file systems.
* As a result, the former pages_io() moved to the VFS layer, and can now be
  called by a file system via {read|write}_file_io_vec_pages() (naming
  suggestions are always welcomed :-)). It now gets an FD, and uses that to
  communicate with the device (via its fs_{read|write}_pages() hooks).
* The file_cache_{read|write}() functions must now be called without holding
  an I/O relevant file system lock. That allows the file cache to prepare the
  pages without colliding with the page writer, IOW the "mayBlock" flag can
  go into the attic again (yay!).
* This also results in a much better performance when the system does I/O and
  is low on memory, as the page writer can now finally write back some pages,
  and that even without maxing out the CPU :)
* The API changes put slightly more burden on the fs_{read|write}_pages()
  hooks, but in combination with the file_map it's still pretty straight
  forward. It just will have to dispatch the call to the underlying device
  directly, usually it will just call its fs_{read|write}_pages() hooks
  via the above mentioned calls.
* Ported BFS and FAT to the new API, the latter has not been tested, though.
* Also ported the API changes to the fs_shell. I also completely removed its
  file cache level page handling - the downside is that device access is no
  longer cached (ie. depends on the host OS now), the upside is that the code
  is greatly simplified.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22886 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/cache/file_map.cpp

@@ -128,7 +128,7 @@ file_map::Add(file_io_vec *vecs, size_t vecCount, off_t &lastOffset)
 		offset += extent->disk.length;
 	}
 
-#ifdef TRACE_FILE_CACHE
+#ifdef TRACE_FILE_MAP
 	for (uint32 i = 0; i < count; i++) {
 		file_extent *extent = ExtentAt(i);
 		dprintf("[%ld] extend offset %Ld, disk offset %Ld, length %Ld\n",
@@ -210,9 +210,24 @@ file_map_delete(void *_map)
 }
 
 
+extern "C" void
+file_map_set_size(void *_map, off_t size)
+{
+	if (_map == NULL)
+		return;
+
+	// TODO: honour offset/size parameters
+	file_map *map = (file_map *)_map;
+	map->Free();
+}
+
+
 extern "C" void
 file_map_invalidate(void *_map, off_t offset, off_t size)
 {
+	if (_map == NULL)
+		return;
+
 	// TODO: honour offset/size parameters
 	file_map *map = (file_map *)_map;
 	map->Free();
@@ -223,6 +238,9 @@ extern "C" status_t
 file_map_translate(void *_map, off_t offset, size_t size, file_io_vec *vecs,
 	size_t *_count)
 {
+	if (_map == NULL)
+		return B_BAD_VALUE;
+
 	file_map &map = *(file_map *)_map;
 	size_t maxVecs = *_count;
 	status_t status = B_OK;