In this project we created a user-level library, libFS, which handles an adequate portion of a file system. We had incorporated our file system into a library that applications can link with to access files and directories. Our library in turn hooks with LibDisk, a library that just mocks behaviors of a "disk".
int FS_Boot(char *path)
FS_Boot() should be called exactly once before any other LibFS functions are called. It receives a single argument, a path, which either points to a real file where your "disk image" is stored or to a file that does not yet exist and which must be created to hold a new disk image. The path is which determined by Operating System. It's not the path in the file system. We can store the disk image file anywhere.
- Upon success, return 0
- Upon failure, return -1 and set osErrno to E_GENERAL
int FS_Sync()
FS_Sync() ensures the contents of the file system are stored persistently on disk.
int File_Create(char *file)
File_Create() creates a new file.
- If the file already exists, function return -1 and set osErrno to E_GENERAL
- File is not going to be open after the create call. File_Create just simply creates a new file on disk of size 0.
- Upon success, return 0
- Upon a failure, return -1 and set osErrno to E_CREATE.
int File_Open(char *file)
File_Open() opens up a file and returns an integer file descriptor ( a number greater than or equal to 0), which can be used to read or write data to that file.
- If the file doesn't exist, return -1 and osErrno is set to E_NO_SUCH_FILE.
- if there are already a maximum number of files open, return -1 and set osErrno to E_TOO_MANY_OPEN_FILES.
int File_Read(int fd, void *buffer, int size)
File_Read() reads size bytes from the file referenced by the file descriptor fd. The data should be read into the buffer pointed to by buffer. All reads should begin at the current locatioin of the file pointer, and file pointer should be updated after the read to the new location.
- If the file is not open, return -1 and set osErrno to E_BAD_FD.
- If the file is open, the number of bytes actually read should be returned, which can be less than or equal to size. (The number could be less than the requested bytes because the end of the file could be reached.)
- If the file pointer is already at the end of the file, zero should be returned, even under repeated calls to File_Read()
int File_Write(int fd, void *buffer, int size)
File_Write() writes size bytes from buffer and write thme into the file referenced by fd. All writes should be updated after the write to its current location plus size.
- Writes are the only way to extend the size of a file.
- If the file is not open, return -1 and set osErrno to E_BAD_F.
- Upon success of the write, all of the data should be written out to disk and the value of the size should be returned.
- If write cannot complete (due to a lack of space), return -1 and set osErrno to E_NO_SPACE.
- If the file exceeds the maximum file size, return -1 and set osErrno to E_FILE_TOO_BIG
int File_Close(int fd)
File_Close() closes the file referred to by file descriptor fd.
- If the file is not currently open, return -1 and set osErrno to E_BAD_FD
- Upon success, return 0.
int File_Unlink(char *file)
This should delete the file referenced by file, including removing its name from the directory it is in, and freeing up any data blocks and inodes that the file was using.
- If the file is currently open, return -1 and set osErrno to E_FILE_IN_USE (and do NOT delete the file).
- Upon success, return 0.
int File_Seek(int fd, int offset)
File_Seek() should update the current location of the file pointer. The location is given as an offset from the beginning of the file.
- If offset is larger than the size of the file or negative, return -1 and set osErrno to E_SEEK_OUT_OF_BOUNDS.
- If the file is not currently open, return -1 and set osErrno to E_BAD_FD.
- Upon success, return the new location of the file pointer.
int Dir_Create(char *path)
Dir_Create() creates a new directory as named by path. To do so, we first allocate a new file (of type directory), and then add a new directory entry in the current directory's parent.
- Upon failure of any sort, return -1 and set osErrno to E_CREATE
- Upon success, return 0.
- Dir_Create() is not recursive (that is, if only "/" exists, and we want to create a directory "/a/b", we must first create "/a", and then create "/a/b").
int Dir_Size(char *path)
Dir_Size() returns the number of bytes in the directory referred to by path. This routine should be used to find the size of the directory before calling Dir_Read() to find the contents of the directory.
int Dir_Read(char *path, void *buffer, int size)
Dir_Read() can be used to read the contents of a directory. It should return in the buffer a set of directory entries. Each entry is of size 20 bytes, and contains 16-byte names of the directories and files within the directory name by path, followed by the 4-byte integer inode number.
- If size is not big enough to contain all of the entries, return -1 and set osErrno to E_BUFFER_TOO_SMALL
- Return the number of directory entries that are in the directory (e.g., 2 if there are two entries in the directory).
int Dir_Unlink(char *path)
Dir_Unlink() removes a directory referred to by path, freeing up its inode and data blocks, and removing its entry from the parent directory.
- Upon success, return 0
- Dir_Unlink() should only be successful if there are no files within the directory. If there are still files within the directory, return -1 and set osErrno to E_DIR_NO_EMPTY.
- If someone tries to remove the root directory("/"), don't allow them to do it! Return -1 and set osErrno to E_ROOT_DIR.
+----+-----+---------------------------------------------+
#2 |. 2 |.. 2 | home 123 | usr 654 | bin 555 |etc 23 | ... |
+----+-----+---------------------------------------------+
| The inode #2 above is the ROOT directory. It has the
| name "home" in it. The *directory* "home" is not
| here; only the *name* is here. The ROOT directory
| itself does not have a name!
V
+------+-----+----------------------------------------------------------------+
#123 |. 123 |.. 2 | ian 111 | file1.txt 755 | file2.txt 883 | file3.txt 221 | ... |
+------+-----+----------------------------------------------------------------+
| The inode #123 above is the "home" directory. The name
| "home" isn't here; it's up in the ROOT directory,
| above. This directory has the name "ian" in it.
V
+----+-------+---------------------------------------------------+
#111 |. 31|.. 123 | foobar 12 | temp 15 | literature 7 | demo 6 | ... |
+----+-------+---------------------------------------------------+
| The inode # above is |
| the "ian" directory. The |
| name "ian" isn't here; |
| it's up in the "home" |
| directory, above. This |
| directory has the names |
| "foobar" and "literature" |
| in it. |
| V
+----+-----+--|-------------------------------------------+
#7 |. 7 |.. 31| | barfoo 12 | morestuf 123 | junk 99 | ... |
+----+-----+--|-------------------------------------------+
| | The inode #7 above is the "literature" directory.
| | The name "literature" isn't here; it's up
| | in the "ian" directory. This directory has
| | the name "barfoo" in it.
| |
V V
*-----------* This inode #12 on the left is a file inode.
| file data | It contains the data blocks for the file.
#12 | file data | This file happens to have two names, "foobar"
| file data | and "barfoo", but those names are not here.
*-----------* The names of this file are up in the two
directories that point to this file, above.
+====================+ +====================+ +====================+
| | | | | |
| directory #2 | | directory #555 | | directory #123 |
| | | | | |
+==============+=====+ +==============+=====+ +==============+=====+
| . (dot) | 2 | | . (dot) | 555 | | . (dot) | 123 |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| .. (dot dot) | 2 | | .. (dot dot) | 2 | | .. (dot dot) | 2 |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| home | 123 | | rm | 546 | | ian | 111 |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| bin | 555 | | ls | 984 | | file1.txt | 755 |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| usr | 654 | | cp | 333 | | file2.txt | 883 |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| | | | ln | 333 | | file3.txt | 221 |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| | | | mv | 333 | | | |
+--------------+-----+ +--------------+-----+ +--------------+-----+
| | | | | 333 | | | |
+==============+=====+ +==============+=====+ +==============+=====+