fs: Added FileSystem::get_block_device

Required for accessing the underlying block device. This can be used to
modify the state of the block device outside of the filesystem.

The best example is if you are reformatting a filesystem:
BlockDevice *bd = fs.get_block_device();
fs.unmount();
FATFileSystem::format(bd);
fs.mount(bd);

Author: geky

features/filesystem/FileSystem.cpp

@@ -44,6 +44,11 @@ int FileSystem::mkdir(const char *path, mode_t mode)
     return -ENOSYS;
 }
 
+BlockDevice *FileSystem::get_block_device() const
+{
+    return NULL;
+}
+
 int FileSystem::file_sync(fs_file_t file)
 {
     return 0;

features/filesystem/FileSystem.h

@@ -99,6 +99,13 @@ class FileSystem : public FileSystemLike {
      */
     virtual int mkdir(const char *path, mode_t mode);
 
+    /** Get the underlying block device
+     *
+     *  @return         The underlying block device, or NULL if no block
+     *                  device has been mounted
+     */
+    virtual BlockDevice *get_block_device() const;
+
 protected:
     friend class File;
     friend class Dir;

features/filesystem/fat/FATFileSystem.cpp

@@ -293,6 +293,15 @@ int FATFileSystem::unmount()
     return fat_error_remap(res);
 }
 
+BlockDevice *FATFileSystem::get_block_device() const
+{
+    if (_id != -1) {
+        return _ffs[_id];
+    } else {
+        return NULL;
+    }
+}
+
 /* See http://elm-chan.org/fsw/ff/en/mkfs.html for details of f_mkfs() and
  * associated arguments. */
 int FATFileSystem::format(BlockDevice *bd, int allocation_unit) {

features/filesystem/fat/FATFileSystem.h

@@ -106,6 +106,13 @@ class FATFileSystem : public FileSystem {
      */
     virtual int mkdir(const char *path, mode_t mode);
 
+    /** Get the underlying block device
+     *
+     *  @return         The underlying block device, or NULL if no block
+     *                  device has been mounted
+     */
+    virtual BlockDevice *get_block_device() const;
+
 protected:
     /** Open a file on the filesystem
      *