diff options
| -rw-r--r-- | fs.c | 98 |
1 files changed, 52 insertions, 46 deletions
@@ -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; - - 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; + struct superblock sb; + + 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; - - bp = bread(dev, 1); - sb = (struct superblock*) bp->data; - ninodes = sb->ninodes; - brelse(bp); + struct superblock sb; + int bi, m; - bp = bread(dev, b); - memset(bp->data, 0, BSIZE); - bwrite(bp); - brelse(bp); + bzero(dev, b); - 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; - - bp = bread(dev, 1); - sb = (struct superblock*)bp->data; - ninodes = sb->ninodes; - brelse(bp); + struct superblock sb; - 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 |