/*
* Allocate a free block, mark it in the freemap and flush the freemap to disk
*/
static blkid sfs_alloc_block()
{
u32 size = sb.nfreemap_blocks * BLOCK_SIZE / sizeof(u32);
// size = 1 * 512 / 4 = 128 four-byte sections = 4096 bits
//Renaming variables i and j to be more specific
u32 fm_blk, fm_byte;
blkid free_block_id;
//Search each freemap block
for(fm_blk = 0; fm_blk < sb.nfreemap_blocks; fm_blk++){
//Read the freemap block located at the block ID
int count;
int freemap_id = fm_blk + 1;
sfs_read_block(freemap, freemap_id);
//Search each index of the freemap block
for(fm_byte = 0; fm_byte < BLOCK_SIZE; fm_byte++){
u32 bitmap = freemap[fm_byte];
if((bitmap ^ 0xffffffff) != 0){
//There is a free bit at this index in the freemap
u32 mask = 0x1;
u32 result;
count = 0;
//Search each bit of the freemap block
while(count < SFS_NBITS_IN_FREEMAP_ENTRY){
result = bitmap & mask;
if(result == mask){
mask = mask << 1;
count++;
} else{
free_block_id = fm_byte * SFS_NBITS_IN_FREEMAP_ENTRY + count;
//Set the bit and flush to disk
u32 newBitmap = bitmap | mask;
freemap[fm_byte] = newBitmap;
sfs_flush_freemap();
//Clear the data stored in the block
char empty_blk[BLOCK_SIZE];
memset(empty_blk, 0, BLOCK_SIZE);
sfs_write_block(empty_blk, free_block_id);
return free_block_id;
}
}
}
}
}
return 0;
}
/*
* Allocate a free block, mark it in the freemap and flush the freemap to disk
*/
static blkid sfs_alloc_block()
{
u32 size = sb.nfreemap_blocks * BLOCK_SIZE / sizeof(u32);
u32 i, j, k;
/* TODO: find a freemap entry that has a free block */
/* TODO: find out which bit in the entry is zero,
set the bit, flush and return the bid
*/
for (i=0; i<size; i++)
{
for (k = 0; k < (sizeof(u32) * 8); k++)
{
j = (freemap[i] & (1 << k));
j = j >> k;
if (j == 0)
{
// Found a free block
freemap[i] |= (1 << k);
sfs_flush_freemap();
return (i * sizeof(u32) + k);
}
}
}
return 0;
}
/*
* Free a block, unmark it in the freemap and flush
*/
static void sfs_free_block(blkid bid)
{
/* TODO find the entry and bit that correspond to the block */
int entry_loc;
int bit_loc;
entry_loc = bid / SFS_NBITS_IN_FREEMAP_ENTRY;
bit_loc = bid % SFS_NBITS_IN_FREEMAP_ENTRY;
/* TODO unset the bit and flush the freemap */
freemap[entry_loc] = (freemap[entry_loc] & ~(1 << bit_loc));
sfs_flush_freemap();
}
/*
* Free a block, unmark it in the freemap and flush
*/
static void sfs_free_block(blkid bid)
{
u32 fm_block;
u32 bitmap;
u32 newBitmap;
u32 mask;
//Find the freemap block and index where the block is
fm_block = bid / (BLOCK_SIZE * 8);
fm_block = fm_block + 1; //Freemap blocks start at BID 1
sfs_read_block(freemap, fm_block);
bitmap = freemap[bid/32];
bitmap = bitmap & ~(1<<(bid%32));
freemap[bid/32] = bitmap;
sfs_flush_freemap();
}