C programming with Unix functions for manipulation of a virtual file system

Hi all,

This virtual file system is implemented as a binary file and I have a problem with some of the functions as it needs to incorporate with Unix and I don't know how/where to start. The basic functions (i.e. manipulation) I had to perform are:

1. Display a directory listing
2. Renaming a file
3. Removing a file
4. Display the contents of each file

The starting point for the program is as follows:

Code:

#define FILE_SYS_SIZE 1024 
#define BLOCK_SIZE 32 
#define DATA_SIZE (BLOCK_SIZE - 2 * sizeof(unsigned char) - sizeof(short)) 
#define FILE_NAME_SIZE (DATA_SIZE-2*sizeof(short)) 
#define HEADER_BLOCK 11 
#define FENTRY_BLOCK 13 
#define DATA_BLOCK   15 
#define FREE_BLOCK   17 
typedef struct 
{ 
        short  size; 
        short  first_block; 
        char name[FILE_NAME_SIZE]; 
} FILE_ENTRY; 
typedef struct 
{ 
        short first_free; 
        short first_used; 
} HEADER; 
typedef struct 
{ 
        unsigned char num; 
        unsigned char type; 
        short next_block; 
        union { 
                HEADER header; 
                FILE_ENTRY fent; 
                char file_content[DATA_SIZE]; 
        } data; 
} BLOCK;

I already have a skeleton code:

Code:

int main() 
{ 
    /*
     * Directory listing & rename calls
     */
    ls(); 
    rename_file("File 1", "File ONE");
    ls();

    /*
     * Displaying the contents of the files
     */
    display( "File TWO" ); 
    display( "File THREE" ); 
    display( "MY FILE" );

    /*
     * Removing a File & Directory Listing
     */
    remove( "File TWO" );
    ls();

    return 0; 
}

My questions are:

1. How and where do I insert the mandatory Unix system functions i.e. open(), read(), write(), lseek(), close() into the program for it to work?

2. How and where do I insert the command to read from a given binary .dat file for it to work?

3. Do I use the rename method as above or the C method:
"int rename(const char *old, const char *new);

Thank you all for your attention and help!

Start with "The basic function 1: Display a directory listing"

What processes do you need to perform?
In what order do you need to do them?

Write it out on paper, then look up the C and Unix functions to accomplish the tasks.

hi walt,

thanks for your advice. am i right to assume that for various unix functions, i use the relevant c functions instead?

e.g.

remove() --> int remove
rename() --> int rename

thanks

>>1. Display a directory listing
look into <dirent.h>
DIR *dp;
struct dirent *dirp;
dp=opendir("dirname");
while((dirp=readdir(dp))!=NULL)
printf("%s\n",dirp->d_name);

>>2. Renaming a file
<stdio.h>
int rename(const char *oldname,const char *newname);

>>3. Removing a file
<stdio.h>
int remove(const char *pathname);

>>4. Display the contents of each file
no direct method

Originally posted by zagelle
hi walt,

thanks for your advice. am i right to assume that for various unix functions, i use the relevant c functions instead?

e.g.

remove() --> int remove
rename() --> int rename

thanks

In general, you use the C functions that do the job. Some of them are named the same as the unix function, but don't necessarily use that as a guide. You're best bet is to look up the relevant C function. in the MAN pages.

For example, you made reference to open() and lseek(). But to accomplish your objective, the lseek() function is not necessary, and fopen() may be easier to use than open(). You will need to decide in C which functions you need.

In your prompts the program displays, it would make sense to reference the Unix command being simulated.