diff --git a/inc/fs.h b/inc/fs.h
index 12ccf30..95bf6cf 100644
--- a/inc/fs.h
+++ b/inc/fs.h
@@ -37,7 +37,7 @@ struct fs_inode_extension {
 
 __attribute__((packed))
 struct fs_directory_record {
-	unsigned char fname[60];
+	unsigned char fname[FS_MAX_FNAME_LEN+1];
 	unsigned int inode_no;
 };
 
diff --git a/src/fs.c b/src/fs.c
index 0b2c65c..02adcaa 100644
--- a/src/fs.c
+++ b/src/fs.c
@@ -26,6 +26,19 @@ static struct fs_file_description fs_file_descriptions[FS_MAX_OPEN_FD];
 
 static int read_block(unsigned int block_no, void *data)
 {
+	// failsafe
+	struct stat st;
+	if (fstat(used_file_fd, &st) < 0) {
+		pr_err("could not stat device '%s'\n", used_file_path);
+		return 0;
+	}
+
+	if (block_no * FS_BLOCK_SIZE >= st.st_size) {
+		pr_err("read beyond device address space denied (%d >= %d)\n",
+				block_no * FS_BLOCK_SIZE, st.st_size);
+		return -1;
+	}
+
 	if (lseek(used_file_fd, block_no * FS_BLOCK_SIZE, SEEK_SET) < 0) {
 		pr_err("failed to seek to block %d (bs=%d) on device '%s'\n", block_no, FS_BLOCK_SIZE, used_file_path);
 		return -1;
@@ -36,6 +49,19 @@ static int read_block(unsigned int block_no, void *data)
 
 static int write_block(unsigned int block_no, void *data)
 {
+	// failsafe
+	struct stat st;
+	if (fstat(used_file_fd, &st) < 0) {
+		pr_err("could not stat device '%s'\n", used_file_path);
+		return 0;
+	}
+
+	if (block_no * FS_BLOCK_SIZE >= st.st_size) {
+		pr_err("write beyond device address space denied (%d >= %d)\n",
+				block_no * FS_BLOCK_SIZE, st.st_size);
+		return -1;
+	}
+
 	if (!write_permitted) {
 		pr_err("write operations are prohibited\n");
 		return -1;
@@ -224,13 +250,40 @@ static unsigned int read_inode_ptr(unsigned int inode_ptr)
 
 		return fsh.inode_ptrs[inode_ptr];
 	} else {
-		pr_err("inode_ptr %d is in fs_header_extension, reading is not implemented\n", inode_ptr);
-		return 0;
-		// TODO: find block with relevant inode_ptr
-		/*
-		unsigned int relevant_block_index = ((free_block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION) + 1;
-		unsigned int relevant_block_record_offset = (free_block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
-		*/
+		// inode_ptr is in fs_header_extension
+		int extension_no = (inode_ptr - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION;
+		int extension_offset = (inode_ptr - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
+
+		struct fs_header fsh;
+		int read_result = read_block(0, &fsh);
+		if (FS_BLOCK_SIZE != read_result) {
+			if (read_result < 0) {
+				pr_err("failed to read fs header from device '%s'\n", used_file_path);
+			} else {
+				pr_err("failed to read full header from device (read %d/%d bytes)\n", read_result, FS_BLOCK_SIZE);
+			}
+
+			return 0;
+		}
+
+		if (!fsh.next_extension)
+			return 0;
+
+		unsigned int next_ext = fsh.next_extension;
+		unsigned int curr_ext = 0;
+
+		struct fs_header_extension ext;
+
+		for (unsigned int i = 0; i < extension_no + 1; i++) {
+			if (!next_ext)
+				return 0;
+
+			curr_ext = next_ext;
+			read_block(curr_ext, (void *) &ext);
+			next_ext = ext.next_extension;
+		}
+
+		return ext.inode_ptrs[extension_offset];
 	}
 }
 
@@ -265,12 +318,73 @@ static void write_inode_ptr(unsigned int inode_ptr, unsigned int block_ptr)
 
 		pr("Updated inode ptr %d -> %d\n", inode_ptr, block_ptr);
 	} else {
-		pr_err("inode_ptr %d is in fs_header_extension, writing is not implemented\n", inode_ptr);
-		// TODO: find block with relevant inode_ptr, extend fs_header if needed
-		/*
-		unsigned int relevant_block_index = ((free_block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION) + 1;
-		unsigned int relevant_block_record_offset = (free_block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
-		*/
+		// inode_ptr is in fs_header_extension
+		int extension_no = (inode_ptr - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION;
+		int extension_offset = (inode_ptr - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
+
+		struct fs_header fsh;
+		int read_result = read_block(0, &fsh);
+		if (FS_BLOCK_SIZE != read_result) {
+			if (read_result < 0) {
+				pr_err("failed to read fs header from device '%s'\n", used_file_path);
+			} else {
+				pr_err("failed to read full header from device (read %d/%d bytes)\n", read_result, FS_BLOCK_SIZE);
+			}
+
+			return;
+		}
+
+		// special case: if header has no extensions, create one
+		// if it was not needed, we would not have ended here in the first place
+		if (!fsh.next_extension) {
+			unsigned int new_block = find_free_block();
+			if (!new_block) {
+				pr_err("failed to allocate block for fs_header_extension\n");
+				return;
+			}
+			mark_used(new_block);
+
+			struct fs_header_extension ext;
+			memset(&ext, 0, sizeof(struct fs_header_extension));
+			write_block(new_block, (void *) &ext);
+
+			fsh.next_extension = new_block;
+			write_block(0, (void *) &fsh);
+		}
+
+		unsigned int next_ext = fsh.next_extension;
+		unsigned int curr_ext = 0;
+
+		struct fs_header_extension ext;
+
+		for (unsigned int i = 0; i < extension_no + 1; i++) {
+			if (!next_ext) {
+				unsigned int new_block = find_free_block();
+				if (!new_block) {
+					pr_err("failed to allocate block for fs_header_extension\n");
+					return;
+				}
+				mark_used(new_block);
+
+				struct fs_header_extension new_ext;
+				memset(&new_ext, 0, sizeof(struct fs_header_extension));
+				write_block(new_block, (void *) &new_ext);
+
+				ext.next_extension = new_block;
+				write_block(curr_ext, (void *) &ext);
+
+				next_ext = new_block;
+			}
+
+			curr_ext = next_ext;
+			read_block(curr_ext, (void *) &ext);
+			next_ext = ext.next_extension;
+		}
+
+		ext.inode_ptrs[extension_offset] = block_ptr;
+		write_block(curr_ext, (void *) &ext);
+
+		pr("Updated inode ptr %d -> %d\n", inode_ptr, block_ptr);
 	}
 }
 
@@ -329,7 +443,7 @@ static int fs_find_free_directory_record(unsigned int dir_inode_ptr)
 
 		if (!dir.blocks[i]) {
 			if (found_block_no < fsh.max_inode_count)
-				return (found_block_no);
+				return found_block_no;
 			else
 				return -1;
 		}
@@ -348,9 +462,43 @@ static int fs_find_free_directory_record(unsigned int dir_inode_ptr)
 	}
 
 	// search in inode extensions
-	// TODO
+	struct fs_inode_extension ext;
 
-	return -1;
+	unsigned int next_ext = dir.next_extension;
+	unsigned int curr_ext = 0;
+
+	while (next_ext) {
+		read_block(next_ext, (void *) &ext);
+		next_ext = ext.next_extension;
+
+		for (unsigned int i = 0; i < BLOCK_ADDRESSES_PER_INODE_EXTENSION; i++) {
+			struct fs_directory_record r[DIRECTORY_RECORDS_PER_BLOCK];
+
+			if (!ext.blocks[i]) {
+				if (found_block_no < fsh.max_inode_count)
+					return found_block_no;
+				else
+					return -1;
+			}
+
+			read_block(ext.blocks[i], (void *) &r);
+
+			for (int j = 0; j < DIRECTORY_RECORDS_PER_BLOCK; j++, found_block_no++) {
+				if (r[j].inode_no)
+					continue;
+
+				if (found_block_no >= fsh.max_inode_count)
+					return -1;
+
+				return found_block_no;
+			}
+		}
+	}
+
+	if (found_block_no >= fsh.max_inode_count)
+		return -1;
+	else
+		return found_block_no;
 }
 
 static int *find_filename_in_directory(unsigned int dir_inode_ptr, char *fname)
@@ -401,19 +549,19 @@ static int fs_add_fname_to_directory(unsigned int dir_inode_ptr, unsigned int ta
 
 	int new_directory_record_index = fs_find_free_directory_record(dir_inode_ptr);
 	if (new_directory_record_index < 0) {
-		pr_err("no free inode pointer found\n");
+		pr_err("no free directory record found\n");
 		return -1;
 	}
 
+	struct fs_inode dir;
+	read_block(read_inode_ptr(dir_inode_ptr), (void *) &dir);
+
 	if (new_directory_record_index < DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE) {
 		// record is located in base inode, writing to it
 		int block_no = new_directory_record_index / DIRECTORY_RECORDS_PER_BLOCK;
 		int block_offset = new_directory_record_index % DIRECTORY_RECORDS_PER_BLOCK;
 
-		struct fs_inode dir_inode;
-		read_block(read_inode_ptr(dir_inode_ptr), (void *) &dir_inode);
-
-		if (dir_inode.blocks[block_no] == 0) {
+		if (dir.blocks[block_no] == 0) {
 			// allocate new block
 			unsigned int new_block = find_free_block();
 			if (new_block == 0) {
@@ -430,31 +578,115 @@ static int fs_add_fname_to_directory(unsigned int dir_inode_ptr, unsigned int ta
 
 			mark_used(new_block);
 
-			dir_inode.blocks[block_no] = new_block;
-			if (dir_inode.size <= block_no * FS_BLOCK_SIZE) {
+			dir.blocks[block_no] = new_block;
+			if (dir.size <= block_no * FS_BLOCK_SIZE) {
 				pr("Updated directory size at inode_ptr=%d: %d -> %d\n",
-						dir_inode_ptr, dir_inode.size, (block_no + 1) * FS_BLOCK_SIZE);
-				dir_inode.size = (block_no + 1) * FS_BLOCK_SIZE;
-				write_block(read_inode_ptr(dir_inode_ptr), (void *) &dir_inode);
+						dir_inode_ptr, dir.size, (block_no + 1) * FS_BLOCK_SIZE);
+				dir.size = (block_no + 1) * FS_BLOCK_SIZE;
+				write_block(read_inode_ptr(dir_inode_ptr), (void *) &dir);
 			}
 		}
 
 		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
-		read_block(dir_inode.blocks[block_no], (void *) &recs);
+		read_block(dir.blocks[block_no], (void *) &recs);
 
 		strcpy(recs[block_offset].fname, fname);
 		recs[block_offset].inode_no = target_inode_ptr;
 
-		write_block(dir_inode.blocks[block_no], (void *) &recs);
+		write_block(dir.blocks[block_no], (void *) &recs);
 
 		pr("Written new directory record #%d for file '%s' (-> inode_ptr=%d) in inode_ptr=%d\n",
 				new_directory_record_index, fname, target_inode_ptr, dir_inode_ptr);
-
-		return 0;
 	} else {
 		// record is located in inode extension
-		// TODO
+		unsigned int extension_no = (new_directory_record_index - (DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE))
+			/ (DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE_EXTENSION);
+		unsigned int extension_block_index = (new_directory_record_index - (DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE))
+			% (DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE_EXTENSION);
+		unsigned int extension_block_offset = (new_directory_record_index - (DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE))
+			% DIRECTORY_RECORDS_PER_BLOCK;
+
+		// seek to next extension
+		// special case
+		if (!dir.next_extension) {
+			unsigned int new_block = find_free_block();
+			if (!new_block) {
+				pr_err("failed to allocate block for fs_inode_extension\n");
+				return -1;
+			}
+			mark_used(new_block);
+
+			struct fs_inode_extension ext;
+			memset(&ext, 0, sizeof(struct fs_inode_extension));
+			write_block(new_block, (void *) &ext);
+
+			dir.next_extension = new_block;
+			write_block(read_inode_ptr(dir_inode_ptr), (void *) &dir);
+		}
+
+		struct fs_inode_extension ext;
+		unsigned int next_ext = dir.next_extension;
+		unsigned int curr_ext = 0;
+
+		for (int i = 0; i < extension_no + 1; i++) {
+			if (!next_ext) {
+				unsigned int new_block = find_free_block();
+				if (!new_block) {
+					pr_err("failed to allocate block for fs_inode_extension\n");
+					return -1;
+				}
+				mark_used(new_block);
+
+				struct fs_inode_extension new_ext;
+				memset(&new_ext, 0, sizeof(struct fs_inode_extension));
+				write_block(new_block, (void *) &new_ext);
+
+				ext.next_extension = new_block;
+				write_block(curr_ext, (void *) &ext);
+
+				next_ext = new_block;
+			}
+
+			curr_ext = next_ext;
+			read_block(curr_ext, (void *) &ext);
+			next_ext = ext.next_extension;
+		}
+
+		struct fs_directory_record r[DIRECTORY_RECORDS_PER_BLOCK];
+
+		if (!ext.blocks[extension_block_index]) {
+			unsigned int new_block = find_free_block();
+			if (!new_block) {
+				pr_err("failed to allocate block for file data\n");
+				return -1;
+			}
+			mark_used(new_block);
+
+			ext.blocks[extension_block_index] = new_block;
+			write_block(curr_ext, (void *) &ext);
+
+			memset(&r, 0, sizeof(r));
+
+			unsigned int dir_size = BLOCK_ADDRESSES_PER_INODE * FS_BLOCK_SIZE
+				+ extension_no * BLOCK_ADDRESSES_PER_INODE_EXTENSION * FS_BLOCK_SIZE
+				+ (extension_block_index + 1) * FS_BLOCK_SIZE;
+			if (dir.size < dir_size) {
+				dir.size = dir_size;
+				write_block(read_inode_ptr(dir_inode_ptr), (void *) &dir);
+			}
+		} else {
+			read_block(ext.blocks[extension_block_index], (void *) &r);
+		}
+
+		r[extension_block_offset].inode_no = target_inode_ptr;
+		strcpy(r[extension_block_offset].fname, fname);
+		write_block(ext.blocks[extension_block_index], (void *) &r);
+
+		pr("Written new directory record #%d for file '%s' (-> inode_ptr=%d) in inode_ptr=%d\n",
+				new_directory_record_index, fname, target_inode_ptr, dir_inode_ptr);
 	}
+
+	return 0;
 }
 
 static int fs_remove_fname_from_directory(unsigned int dir_inode_ptr, char *fname)
@@ -724,6 +956,8 @@ static int write_fd_block(unsigned int fd, unsigned int block_index, unsigned ch
 				struct fs_inode_extension ext;
 				memset(&ext, 0, sizeof(struct fs_inode_extension));
 				write_block(target_extension_address, (void *) &ext);
+
+				target_extension_address = new_block;
 			}
 
 			struct fs_inode_extension ext;
@@ -894,7 +1128,8 @@ int fs_write(void *d)
 	read_block(fs_file_descriptions[fd].inode, (void *) &f);
 
 	if (fs_file_descriptions[fd].rw_offset > f.size) {
-		pr("Increasing fd %d file size: %d -> %d\n", fd, f.size, f.size + str_len);
+		pr("Increasing fd %d file size: %d -> %d\n",
+				fd, f.size, fs_file_descriptions[fd].rw_offset);
 		f.size = fs_file_descriptions[fd].rw_offset;
 		write_block(fs_file_descriptions[fd].inode, (void *) &f);
 	}
@@ -1082,8 +1317,8 @@ int fs_create(void *d)
 		}
 	}
 
-	if (fname_len > 59) {
-		pr_err("filename too long (%d > %d)\n", fname_len, 59);
+	if (fname_len > FS_MAX_FNAME_LEN) {
+		pr_err("filename too long (%d > %d)\n", fname_len, FS_MAX_FNAME_LEN);
 		return 0;
 	}
 
@@ -1154,8 +1389,8 @@ int fs_ln(void *d)
 	}
 
 
-	if (new_fname_len > 59) {
-		pr_err("new filename too long (%d > 59)\n", new_fname_len);
+	if (new_fname_len > FS_MAX_FNAME_LEN) {
+		pr_err("new filename too long (%d > %d)\n", new_fname_len, FS_MAX_FNAME_LEN);
 		return 0;
 	}
 
@@ -1246,22 +1481,44 @@ int fs_ls(void *d)
 
 	// list entries from base inode
 	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
-		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
+		if (!dir.blocks[i])
+			continue;
 
-		if (dir.blocks[i]) {
-			read_block(dir.blocks[i], (void *) &recs);
+		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
+		read_block(dir.blocks[i], (void *) &recs);
+
+		for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
+			if (!recs[k].inode_no)
+				continue;
+
+			pr_stdout("%s -> inode_ptr=%d\n", recs[k].fname, recs[k].inode_no);
+		}
+	}
+
+	// list entries from inode extension
+	struct fs_inode_extension ext;
+	unsigned int next_ext = dir.next_extension;
+
+	while (next_ext) {
+		read_block(next_ext, (void *) &ext);
+		next_ext = ext.next_extension;
+
+		for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE_EXTENSION; i++) {
+			if (!ext.blocks[i])
+				continue;
+
+			struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
+			read_block(ext.blocks[i], (void *) &recs);
 
 			for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
 				if (!recs[k].inode_no)
 					continue;
 
-				pr_stdout("%s\n", recs[k].fname);
+				pr_stdout("%s -> inode_ptr=%d\n", recs[k].fname, recs[k].inode_no);
 			}
 		}
 	}
 
-	// list entries from inode extension
-	// TODO
 
 	return 0;
 }
@@ -1282,10 +1539,46 @@ int fs_la(void *d)
 
 	// list entries from base inode
 	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
-		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
+		if (!dir.blocks[i])
+			continue;
 
-		if (dir.blocks[i]) {
-			read_block(dir.blocks[i], (void *) &recs);
+		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
+		read_block(dir.blocks[i], (void *) &recs);
+
+		for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
+			if (!recs[k].inode_no)
+				continue;
+
+			struct fs_inode f_inode;
+			read_block(read_inode_ptr(recs[k].inode_no), (void *) &f_inode);
+
+			if (f_inode.ftype == DIRECTORY) {
+				pr_stdout(COLOR_BLUE "%s" COLOR_RESET
+						" (inode_ptr=%d -> inode=%d, ref_count=%d, size=%d, type=dir)\n",
+						recs[k].fname, recs[k].inode_no, read_inode_ptr(recs[k].inode_no),
+						f_inode.ref_count, f_inode.size);
+			} else {
+				pr_stdout("%s (inode_ptr=%d -> inode=%d, ref_count=%d, size=%d, type=reg)\n",
+						recs[k].fname, recs[k].inode_no, read_inode_ptr(recs[k].inode_no),
+						f_inode.ref_count, f_inode.size);
+			}
+		}
+	}
+
+	// list entries from inode extension
+	struct fs_inode_extension ext;
+	unsigned int next_ext = dir.next_extension;
+
+	while (next_ext) {
+		read_block(next_ext, (void *) &ext);
+		next_ext = ext.next_extension;
+
+		for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE_EXTENSION; i++) {
+			if (!ext.blocks[i])
+				continue;
+
+			struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
+			read_block(ext.blocks[i], (void *) &recs);
 
 			for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
 				if (!recs[k].inode_no)
@@ -1296,7 +1589,7 @@ int fs_la(void *d)
 
 				if (f_inode.ftype == DIRECTORY) {
 					pr_stdout(COLOR_BLUE "%s" COLOR_RESET
-							"(inode_ptr=%d -> inode=%d, ref_count=%d, size=%d, type=dir)\n",
+							" (inode_ptr=%d -> inode=%d, ref_count=%d, size=%d, type=dir)\n",
 							recs[k].fname, recs[k].inode_no, read_inode_ptr(recs[k].inode_no),
 							f_inode.ref_count, f_inode.size);
 				} else {
@@ -1308,9 +1601,6 @@ int fs_la(void *d)
 		}
 	}
 
-	// list entries from inode extension
-	// TODO
-
 	return 0;
 }