ENGR 3950U / CSCI 3020U: Operating Systems

Description and C Code of Major Functions in Simulated Unix File System.

Instructor:

Dr. Kamran SartipiFaculty of Engineering and Applied Science

UOIT

Canada

Pathname Parsing

int parse_pathname (char *path, int*no_ofcomponents) • pathname, such as “/foo/bar/kamra/new”, stored in

data_buff_1[1024]

• Scan from left to right and check the validity of the pathname. - start with “/” and number of characters less than 6.

• Put valid component in one of the rows of two dimensional array pathname_parse[64][7].

• Return the number of pathname components, “no_ofcomponents”.

Errors reported

• Input : foo/bar/kamra/new

Path name should start from root dir, (begin with ‘/’)

• Input: /foo/bar//kamra/new

Zero length component.  

• Input: /foo/bar/kamran/new

Components more than 5 characters

C code of parse_pathname

int parse_pathname(char *path, int *no_ofcomponents) { int i, j=0, k if(path[0] !='/'){ return (-14); } for(i=1; i<=1023; i++) { if((path[i] == '/') && (k==0)) { return (-15); } if(k<=4) { /****** k <=4 ******/ /* length of pathname is valid. */ if(path[i] == '\0') { /* end of parsing. */

C code of parse_pathname

while (k<=5) { pathname_parse[j][k] = '\0'; k++; } *no_ofcomponents = j+1; return (0); } if(path[i] != '/') { /* current pathname is valid. */ pathname_parse[j][k] = path[i]; k++; } else { /*another component is started. */

C code of parse_pathname

while(k<=5){ pathname_parse[j][k] = '\0'; k++; } k=0; j++; /* next pathname component. */ } } else { /****** k == 5 ******/ if(path[i] == '\0') { /* end of parsing. */ *no_ofcomponents = j+1; return (0); } else { if(path[i] == '/') pathname_parse[j][k] = '\0';

C code of parse_pathname

k=0; j++; /* set for next pathname component. */ } else { /* length of pathname is invalid. */ return (-16); } } } } }

Directory Manipulation

• Directory is a file and consists of a number of directory entries.

• Each entry consists of 10 bytes, as follows: i) 6 bytes for "name" of the pathname

component. ii) 2 bytes for the "i_number" of the pathname component. iii) 2 bytes unused.

• Each block of directory file can hold 12 directory entries. 12 * 10 = 120 < 128 bytes (block size).

Pathname Translation• Begin from the "root directory”:

• Parse the pathname and put its components into the pathname array “pathname_parse[64][7]”.

• Take the first parsed name from the first row of "pathname_parse[64][7]"

• Search in the root directory for the “I_number” of the first pathname component.

• Use the “I_number“ to access the data blocks for this pathname component into buffers.

• Take the second pathname component from "pathname_parse[64][7]" and searches till last pathname component.

C code of Dir_search

int dir_search(char *component, int *i_number) { int i,temp_inumber,block_no, index, type,file_ptr, dir_blocks, flag; /* root directory "*i_number = 0". */ temp_inumber = *i_number; if(get_file_pointer(temp_inumber, &file_ptr)<0) return (-1); } if(get_file(temp_inumber, &type)<0){ return (-1); }

C code of Dir_search

if(type == 0) { return (-1); } flag = compare_component_tobuff( component, &index, &temp_inumber); if(flag == 0) { /* match is found. */ *i_number = temp_inumber; return (0); } /* component is not found. */ return (1); }

Pseudo-code for Create

Int sfs_create (char *pathname, int type):

get the I_node table. parse the pathname. while pathname component is not the last component if(i_number ==0) then Error.(0) if intermediate file is regular file, then Error.(1) get the next component.

Pseudo-code for Create

search in the parent directory for the new component: if component is found, get the i_number and go to the loop to search for the next pathname

component. else Error.(2) end while if the file already existed Error.(3)**** used for every pathname manipulations ****

Pseudo-code for Create

- Search for empty i_node table entry.- Search for free disk block.- Put the "free block number" in the - i_node table. - Make a directory entry- Write the directory entry “(fileName,

i_number)” in the parent directory.- Put i_node table back in the disk.

Pseudo-code for sfs_delete

Perform the process for the pathnamemanipulation.

if the file is a regular file get the reference counter of the file. if reference counter > 0 then Error. else release all blocks of the regular file. set file pointer to 0 

Pseudo-code for sfs_delete

if the file is a directory file: get the file if the directory is not empty then

Error. . get the reference counter of the file. if reference counter > 0 then Error. else release all blocks of the regular file. set file pointer to 0.

Pseudo-code for sfs_delete

- Get the file of the parent directory.

- Erase the directory entry of the deleted file.

- Put the parent directory file back to the disk.

GOOD LUCK!!