ffs.c

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//ffs.c -- flat file system
#include "ffs.h"
#include "ide.h"
#include "../lib/err.h"
#include "../io/io.h"
 
/**
 * @brief ffsinit initializes the flat filesystem on disk
 *
 * ffsinit is a function that reads and validates the boot sector
 * checking for the 0x55 0xAA boot signature and verifying sector size
 * it also creates an empty filesystem table if one doesnt exist yet
 *
 * using ffsinit is done with
 * @code{.c}
 * #include "../fs/ffs.h" //or just ffs.h
 * ffsinit();
 * @endcode
 *
 * @see ideinit(), fsinit(), boot.s
 */
void __ffsinit(void) {
    uint8_t sector[512]; //make sector val
    
    //read boot sector
    irsec(0, sector); //read via ide
    
    //check boot signature
    assert(sector[510] == 0x55 && sector[511] == 0xAA, "ffs: no boot signature");
 
    //sanity check values
    uint16_t bps = sector[11] | (sector[12] << 8);
    assert(bps == 512, "ffs: bytes per sector not 512");
    
    uint8_t spc = sector[13];
    assert(spc > 0 && spc <= 128, "ffs: invalid sectors per cluster");
    
    //create fs table if it doesnt exist
    uint8_t table[512];
    irsec(1, table);
    if (table[0] != 'F' || table[1] != 'S') {
        //no filesystem yet, create empty one
        for (int i = 0; i < 512; i++) table[i] = 0;
        table[0] = 'F';
        table[1] = 'S';
        table[2] = 0; //file_count = 0
        iwrt(1, table);
    }
}
 
/**
 * @brief disksize returns the total disk size in kilobytes
 *
 * disksize is a function that queries the ide drive for its total sector count
 * and converts it to kilobytes
 *
 * using disksize is done with
 * @code{.c}
 * #include "../fs/ffs.h" //or just ffs.h
 * uint32_t dsize = disksize();
 * @endcode
 *
 * @see idesize(), memsize()
 */
uint32_t __disksize(void) {
    uint32_t secs;
    if (idesize(&secs)) {
        return (secs * 512) / 1024; //convert to kb
    }
    return 0;
}