add symlink command

config.h

@@ -27,6 +27,7 @@
 #define FS_MAX_OPEN_FD 32
 #define FS_MAX_FNAME_LEN 11
 #define FS_MAX_DIRECTORY_DEPTH 512
+#define FS_MAX_SYMLINK_FOLLOWING_DEPTH 1024
 
 
 #endif

inc/fs.h

@@ -4,7 +4,8 @@
 
 enum fs_filetype {
 	REGULAR,
-	DIRECTORY
+	DIRECTORY,
+	SYMLINK
 };
 
 __attribute__((packed))
@@ -73,6 +74,7 @@ int fs_close(void *d);
 int fs_mkdir(void *d);
 int fs_rmdir(void *d);
 int fs_cd(void *d);
+int fs_symlink(void *d);
 int fs_truncate(void *d);
 int fs_allow_write(void *d);
 int fs_prohibit_write(void *d);

src/cli.c

@@ -29,6 +29,7 @@ static const struct CliCommandEntry cmd[] = {
 	{"mkdir", 1, (enum CliArgType[]) {STR}, fs_mkdir},
 	{"rmdir", 1, (enum CliArgType[]) {STR}, fs_rmdir},
 	{"cd", 1, (enum CliArgType[]) {STR}, fs_cd},
+	{"symlink", 2, (enum CliArgType[]) {STR, STR}, fs_symlink},
 
 	// custom commands
 	{"use", 1, (enum CliArgType[]) {STR}, fs_use},

src/fs.c

@@ -190,6 +190,16 @@ static unsigned int find_free_block(void)
 	return 0;
 }
 
+static unsigned int claim_free_block(void)
+{
+	int free_block = find_free_block();
+
+	if (free_block)
+		mark_used(free_block);
+
+	return free_block;
+}
+
 static unsigned int find_free_inode_ptr(void)
 {
 	unsigned int i = 1;  // inode0 always points to root dir, so can't be free
@@ -1584,6 +1594,12 @@ int fs_ln(void *d)
 		}
 	}
 
+	/*
+	 * TODO: add support for directory as target, e. g.:
+	 * $ create file1
+	 * $ mkdir dir2
+	 * $ ln file1 dir2 -> creates hardlink 'dir2/file1'
+	 */
 	resolve_path(&new_rp, new_path, 1);
 	if (new_rp.parent_inode_ptr < 0) {
 		pr_err("failed to create hard link: no such directory: '%s'\n", new_path);
@@ -1615,6 +1631,156 @@ int fs_ln(void *d)
 	return 0;
 }
 
+int fs_symlink(void *d)
+{
+	char *target_path = ((char **) d)[0];
+	char *link_path = ((char **)d)[1];
+
+	int target_path_len = strlen(target_path);
+
+	struct resolved_path rp;
+	resolve_path(&rp, link_path, FOLLOW_LAST_SYMLINK);
+
+	if (rp.parent_inode_ptr < 0) {
+		pr_err("failed to create symlink: no such directory: '%s'\n", link_path);
+		return 0;
+	}
+
+	char link_fname[FS_MAX_FNAME_LEN+1];
+	unsigned int dir_inode_ptr;
+
+	if (rp.target_inode_ptr >= 0) {
+		{
+			struct fs_inode i;
+			read_block(read_inode_ptr(rp.target_inode_ptr), &i);
+
+			if (i.ftype == REGULAR) {
+				pr_err("file already exists: '%s'\n", rp.target_fname);
+				return 0;
+			} else {
+				int link_fname_len = extract_basename(target_path, link_fname);
+				if (link_fname_len > FS_MAX_FNAME_LEN) {
+					pr_err("new filename too long (%d > %d)\n", link_fname_len, FS_MAX_FNAME_LEN);
+					return 0;
+				}
+
+				dir_inode_ptr = rp.target_inode_ptr;
+			}
+		}
+	} else {
+		int link_fname_len = extract_basename(link_path, link_fname);
+		if (link_fname_len > FS_MAX_FNAME_LEN) {
+			pr_err("new filename too long (%d > %d)\n", link_fname_len, FS_MAX_FNAME_LEN);
+			return 0;
+		}
+
+		dir_inode_ptr = rp.parent_inode_ptr;
+	}
+
+	int inode_ptr = find_free_inode_ptr();
+	if (!inode_ptr) {
+		pr_err("no free inode_ptr found\n");
+		return 0;
+	}
+
+	int inode_addr = claim_free_block();
+	if (!inode_addr) {
+		pr_err("no space left on device\n");
+		return 0;
+	}
+
+	write_inode_ptr(inode_ptr, inode_addr);
+
+	int required_block_amount = target_path_len % FS_BLOCK_SIZE
+		? target_path_len / FS_BLOCK_SIZE + 1
+		: target_path_len / FS_BLOCK_SIZE;
+
+	int inode_blocks[required_block_amount];
+
+	for (int i = 0; i < required_block_amount; i++) {
+		inode_blocks[i] = claim_free_block();
+		if (!inode_blocks[i]) {
+			pr_err("no space left on device\n");
+			return 0;
+		}
+	}
+
+	int bytes_written = 0;
+	int blocks_written = 0;
+
+	struct fs_inode i;
+	memset(&i, 0, sizeof(i));
+
+	i.ftype = SYMLINK;
+	i.ref_count = 1;
+	i.size = target_path_len;
+
+	for (int j = 0; j < BLOCK_ADDRESSES_PER_INODE; j++, blocks_written++) {
+		i.blocks[j] = inode_blocks[blocks_written];
+		write_block(inode_addr, &i);
+
+		if (target_path_len - bytes_written < FS_BLOCK_SIZE) {
+			char data_block[FS_BLOCK_SIZE];
+			memset(data_block, 0, sizeof(data_block));
+			memcpy(data_block, &(target_path[bytes_written]), target_path_len - bytes_written);
+			write_block(inode_blocks[blocks_written], data_block);
+			bytes_written = target_path_len;
+		} else {
+			write_block(inode_blocks[blocks_written], &(target_path[bytes_written]));
+			bytes_written += FS_BLOCK_SIZE;
+		}
+
+		if (target_path_len == bytes_written)
+			goto finish_writing;
+	}
+
+	i.next_extension = claim_free_block();
+	if (!i.next_extension) {
+		pr_err("no space left on device\n");
+		return 0;
+	}
+	write_block(inode_addr, &i);
+
+	for (unsigned int next_ext = i.next_extension; ; ) {
+		struct fs_inode_extension ext;
+		memset(&ext, 0, sizeof(ext));
+
+		for (int j = 0; j < BLOCK_ADDRESSES_PER_INODE_EXTENSION; j++, blocks_written++) {
+			ext.blocks[j] = inode_blocks[blocks_written];
+			write_block(next_ext, &ext);
+
+			if (target_path_len - bytes_written < FS_BLOCK_SIZE) {
+				char data_block[FS_BLOCK_SIZE];
+				memset(data_block, 0, sizeof(data_block));
+				memcpy(data_block, &(target_path[bytes_written]), target_path_len - bytes_written);
+				write_block(inode_blocks[blocks_written], data_block);
+				bytes_written = target_path_len;
+			} else {
+				write_block(inode_blocks[blocks_written], &(target_path[bytes_written]));
+				bytes_written += FS_BLOCK_SIZE;
+			}
+
+			if (target_path_len == bytes_written)
+				goto finish_writing;
+		}
+
+		ext.next_extension = claim_free_block();
+		if (!ext.next_extension) {
+			pr_err("no space left on device\n");
+			return 0;
+		}
+		write_block(next_ext, &ext);
+
+		next_ext = ext.next_extension;
+	}
+
+finish_writing:
+	pr("Symlink '%s' written successfully (%d/%d bytes)\n", link_fname, bytes_written, target_path_len);
+
+	fs_add_fname_to_directory(dir_inode_ptr, inode_ptr, link_fname);
+	return 0;
+}
+
 
 static int last_significant_slash_position(char *path, int path_len)
 {
@@ -1637,12 +1803,9 @@ static int extract_basename(char *path, char *name)
 	if (fname_len > FS_MAX_FNAME_LEN) {
 		pr_err("filename too long (%d > %d)",
 				fname_len, FS_MAX_FNAME_LEN);
-		return -1;
-	}
-
-	// allow the usage of NULL ptr to discard basename string
-	if (name)
+	} else if (name) {
 		strcpy(name, &(path[lsp+1]));
+	}
 
 	return fname_len;
 }