sanchayanmaity/xv6-cs450
1
0
Fork 0
Code Issues Pull requests Packages Projects Releases Wiki Activity

FS cleanup.

Browse source 
Add utility routines bzero, readsb so that balloc, bfree fit on one page.
Make balloc loop clearer.
This commit is contained in:
rsc 2007-08-27 14:20:24 +00:00
parent d003d232fc
commit a505fd6651
1 changed files with 51 additions and 45 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

96
fs.c
View file

@ -1,6 +1,4 @@
// File system implementation.
//
// Four layers:
// File system implementation. Four layers:
// + Blocks: allocator for raw disk blocks.
// + Files: inode allocator, reading, writing, metadata.
// + Directories: inode with special contents (list of other inodes!)
@ -28,34 +26,53 @@
#define min(a, b) ((a) < (b) ? (a) : (b))
static void itrunc(struct inode*);
// Read the super block.
static void
readsb(int dev, struct superblock *sb)
{
struct buf *bp;
bp = bread(dev, 1);
memmove(sb, bp->data, sizeof(*sb));
brelse(bp);
}
// Zero a block.
static void
bzero(int dev, int bno)
{
struct buf *bp;
bp = bread(dev, bno);
memset(bp->data, 0, BSIZE);
bwrite(bp);
brelse(bp);
}
// Blocks.
// Allocate a disk block.
static uint
balloc(uint dev)
{
int b, bi, m, ninodes, size;
int b, bi, m;
struct buf *bp;
struct superblock *sb;
struct superblock sb;
bp = bread(dev, 1);
sb = (struct superblock*) bp->data;
size = sb->size;
ninodes = sb->ninodes;
for(b = 0; b < size; b++) {
if(b % BPB == 0) {
brelse(bp);
bp = bread(dev, BBLOCK(b, ninodes));
}
bi = b % BPB;
m = 0x1 << (bi % 8);
if((bp->data[bi/8] & m) == 0) { // is block free?
bp->data[bi/8] |= m;
bwrite(bp); // mark it allocated on disk
brelse(bp);
return b;
bp = 0;
readsb(dev, &sb);
for(b = 0; b < sb.size; b += BPB){
bp = bread(dev, BBLOCK(b, sb.ninodes));
for(bi = 0; bi < BPB; bi++){
m = 1 << (bi % 8);
if((bp->data[bi/8] & m) == 0){ // Is block free?
bp->data[bi/8] |= m; // Mark block in use on disk.
bwrite(bp);
brelse(bp);
return b + bi;
}
}
brelse(bp);
}
panic("balloc: out of blocks");
}
@ -65,26 +82,19 @@ static void
bfree(int dev, uint b)
{
struct buf *bp;
struct superblock *sb;
int bi, m, ninodes;
struct superblock sb;
int bi, m;
bp = bread(dev, 1);
sb = (struct superblock*) bp->data;
ninodes = sb->ninodes;
brelse(bp);
bzero(dev, b);
bp = bread(dev, b);
memset(bp->data, 0, BSIZE);
bwrite(bp);
brelse(bp);
bp = bread(dev, BBLOCK(b, ninodes));
readsb(dev, &sb);
bp = bread(dev, BBLOCK(b, sb.ninodes));
bi = b % BPB;
m = 0x1 << (bi % 8);
m = 1 << (bi % 8);
if((bp->data[bi/8] & m) == 0)
panic("freeing free block");
bp->data[bi/8] &= ~m;
bwrite(bp); // mark it free on disk
bp->data[bi/8] &= ~m; // Mark block free on disk.
bwrite(bp);
brelse(bp);
}
@ -252,17 +262,13 @@ iunlockput(struct inode *ip)
struct inode*
ialloc(uint dev, short type)
{
int inum, ninodes;
int inum;
struct buf *bp;
struct dinode *dip;
struct superblock *sb;
struct superblock sb;
bp = bread(dev, 1);
sb = (struct superblock*)bp->data;
ninodes = sb->ninodes;
brelse(bp);
for(inum = 1; inum < ninodes; inum++) { // loop over inode blocks
readsb(dev, &sb);
for(inum = 1; inum < sb.ninodes; inum++) { // loop over inode blocks
bp = bread(dev, IBLOCK(inum));
dip = &((struct dinode*)(bp->data))[inum % IPB];
if(dip->type == 0) { // a free inode