libports: extend FUSE implementation

* add sync method:
  Since file systems tend to have a inbuild caching mechansim we need to
  sync these caches at the end of session when using the fuse_fs server.
  Therefore each FUSE file system port has to implement a Fuse::sync_fs()
  function that executes the necessary actions if requested.

* add symlink check

* allow to check FUSE fs initialization
  This changes the private API of the FUSE implementation. The init_fs
  method now has to return true if the initialization was successful and
  otherwise false. All current users of the API are also changed
  accordingly.

Fixes #1058.

libports/include/fuse/fuse_private.h

@@ -77,10 +77,37 @@ namespace Fuse {
 
 	bool initialized();
 
-	/* Genode fuse filesystem init functions */
-	void init_fs();
+	/**
+	 * Initialize the file system
+	 *
+	 * Mount the medium containg the file system, e.g. by
+	 * using a Block_session connection, and call the file system
+	 * init function as well as initialize needed fuse structures.
+	 */
+	bool init_fs();
+
+	/**
+	 * Deinitialize the file system
+	 *
+	 * Unmount the medium, call the file system cleanup function
+	 * and free all fuse structures.
+	 */
 	void deinit_fs();
 
+	/**
+	 * Synchronize the file system
+	 *
+	 * Request the file system to flush all internal caches
+	 * to disk.
+	 */
+	void sync_fs();
+
+	/**
+	 * FUSE File system implementation supports symlinks
+	 */
+	bool support_symlinks();
+
+	/* list of FUSE operations as of version 2.6 */
 	enum Fuse_operations {
 		FUSE_OP_GETATTR     =  0,
 		FUSE_OP_READLINK    =  1,

libports/src/lib/exfat/init.cc

@@ -29,25 +29,38 @@ struct exfat ef;
 
 }
 
-void Fuse::init_fs(void)
+
+bool Fuse::init_fs(void)
 {
 	PLOG("libc_fuse_exfat: try to mount /dev/blkdev...");
 
 	int err = exfat_mount(&ef, "/dev/blkdev", "");
 	if (err) {
 		PERR("libc_fuse_exfat: could not mount /dev/blkdev");
-		return;
+		return false;
 	}
 
 	fh = fuse_new(fc, NULL, &fuse_exfat_ops, sizeof (struct fuse_operations), NULL);
 	if (fh == 0) {
 		PERR("libc_fuse_exfat: fuse_new() failed");
-		return;
+		return false;
 	}
+
+	return true;
 }
 
+
 void Fuse::deinit_fs(void)
 {
 	PLOG("libc_fuse_exfat: umount /dev/blkdev...");
 	exfat_unmount(&ef);
 }
+
+
+void Fuse::sync_fs(void) { }
+
+
+bool Fuse::support_symlinks(void)
+{
+	return false;
+}

libports/src/lib/fuse-ext2/init.cc

@@ -36,21 +36,22 @@ static struct extfs_data extfs_data;
 
 }
 
-void Fuse::init_fs(void)
+
+bool Fuse::init_fs(void)
 {
 	PLOG("libc_fuse_ext2: try to mount /dev/blkdev...");
 
 	int err = ext2fs_open("/dev/blkdev",  EXT2_FLAG_RW, 0, 0, unix_io_manager, &e2fs);
 	if (err) {
 		PERR("libc_fuse_ext2: could not mount /dev/blkdev, error: %d", err);
-		return;
+		return false;
 	}
 
 	errcode_t rc = ext2fs_read_bitmaps(e2fs);
 	if (rc) {
 		PERR("libc_fuse_ext2: error while reading bitmaps");
 		ext2fs_close(e2fs);
-		return;
+		return false;
 	}
 
 	extfs_data.debug = 0;
@@ -67,12 +68,28 @@ void Fuse::init_fs(void)
 	fh = fuse_new(fc, NULL, &ext2fs_ops, sizeof (ext2fs_ops), &extfs_data);
 	if (fh == 0) {
 		PERR("libc_fuse_ext2: fuse_new() failed");
-		return;
+		return false;
 	}
+
+	return true;
 }
 
+
 void Fuse::deinit_fs(void)
 {
 	PLOG("libc_fuse_ext2: unmount /dev/blkdev...");
 	ext2fs_close(e2fs);
 }
+
+
+void Fuse::sync_fs(void)
+{
+	PLOG("libc_fuse_ext2: sync file system...");
+	ext2fs_flush(e2fs);
+}
+
+
+bool Fuse::support_symlinks(void)
+{
+	return true;
+}

libports/src/lib/libc_fuse/plugin.cc

@@ -129,12 +129,16 @@ namespace {
 			 */
 			Plugin()
 			{
-				Fuse::init_fs();
+				if (!Fuse::init_fs()) {
+					PERR("FUSE fs initialization failed");
+					return;
+				}
 			}
 
 			~Plugin()
 			{
-				Fuse::deinit_fs();
+				if (Fuse::initialized())
+					Fuse::deinit_fs();
 			}
 
 			bool supports_mkdir(const char *path, mode_t mode)