block bitmap

balloc

fs.c

@@ -16,6 +16,43 @@ struct spinlock inode_table_lock = { "inode_table" };
 
 uint rootdev = 1;
 
+static uint 
+balloc(uint dev) 
+{
+  int b;
+  struct buf *bp;
+  struct superblock *sb;
+  int bi;
+  int size;
+  int ninodes;
+  uchar m;
+
+  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?
+      break;
+    }
+  }
+  if (b >= size)
+    panic("balloc: out of blocks\n");
+
+  cprintf ("balloc: allocate block %d\n", b);
+  bp->data[bi/8] |= 0x1 << (bi % 8);
+  bwrite (dev, bp, BBLOCK(b, ninodes));  // mark it allocated on disk
+  return b;
+}
+
+
 // returns an inode with busy set and incremented reference count.
 struct inode *
 iget(uint dev, uint inum)
@@ -51,7 +88,7 @@ iget(uint dev, uint inum)
 
   release(&inode_table_lock);
 
-  bp = bread(dev, inum / IPB + 2);
+  bp = bread(dev, IBLOCK(inum));
   dip = &((struct dinode *)(bp->data))[inum % IPB];
   nip->type = dip->type;
   nip->major = dip->major;
@@ -76,12 +113,12 @@ ialloc(uint dev, short type)
   struct buf *bp;
 
   bp = bread(dev, 1);
-  sb = (struct superblock *) bp;
+  sb = (struct superblock *) bp->data;
   ninodes = sb->ninodes;
   brelse(bp);
 
   for (inum = 1; inum < ninodes; inum++) {  // loop over inode blocks
-    bp = bread(dev, inum / IPB + 2);
+    bp = bread(dev, IBLOCK(inum));
     dip = &((struct dinode *)(bp->data))[inum % IPB];
     if (dip->type == 0) {  // a free inode
       break;
@@ -90,13 +127,12 @@ ialloc(uint dev, short type)
   }
  
   if (inum >= ninodes) {
-    cprintf ("ialloc: no inodes left\n");
+    panic ("ialloc: no inodes left\n");
-    return 0;
   }
 
   cprintf ("ialloc: %d\n", inum);
   dip->type = type;
-  bwrite (dev, bp, inum / IPB + 2);   // mark it allocated on the disk
+  bwrite (dev, bp, IBLOCK(inum));   // mark it allocated on the disk
   brelse(bp);
   ip = iget (dev, inum);
   return ip;
@@ -108,14 +144,14 @@ iupdate (struct inode *ip)
   struct buf *bp;
   struct dinode *dip;
 
-  bp = bread(ip->dev, ip->inum / IPB + 2);
+  bp = bread(ip->dev, IBLOCK(ip->inum));
   dip = &((struct dinode *)(bp->data))[ip->inum % IPB];
   dip->type = ip->type;
   dip->major = ip->major;
   dip->minor = ip->minor;
   dip->nlink = ip->nlink;
   dip->size = ip->size;
-  bwrite (ip->dev, bp, ip->inum / IPB + 2);   // mark it allocated on the disk
+  bwrite (ip->dev, bp, IBLOCK(ip->inum));   // mark it allocated on the disk
   brelse(bp); 
 }
 
@@ -203,10 +239,10 @@ readi(struct inode *ip, void *xdst, uint off, uint n)
   struct buf *bp;
 
   while(n > 0 && off < ip->size){
-    bp = bread(ip->dev, bmap(ip, off / 512));
+    bp = bread(ip->dev, bmap(ip, off / BSIZE));
     n1 = min(n, ip->size - off);
-    n1 = min(n1, 512 - (off % 512));
+    n1 = min(n1, BSIZE - (off % BSIZE));
-    memmove(dst, bp->data + (off % 512), n1);
+    memmove(dst, bp->data + (off % BSIZE), n1);
     n -= n1;
     off += n1;
     dst += n1;
@@ -241,10 +277,10 @@ namei(char *path)
       return 0;
     }
 
-    for(off = 0; off < dp->size; off += 512){
+    for(off = 0; off < dp->size; off += BSIZE){
-      bp = bread(dp->dev, bmap(dp, off / 512));
+      bp = bread(dp->dev, bmap(dp, off / BSIZE));
       for(ep = (struct dirent *) bp->data;
-          ep < (struct dirent *) (bp->data + 512);
+          ep < (struct dirent *) (bp->data + BSIZE);
           ep++){
         if(ep->inum == 0) 
           continue;
@@ -288,10 +324,10 @@ mknod(struct inode *dp, char *cp, short type, short major, short minor)
   ip->major = major;
   ip->minor = minor;
 
-  for(off = 0; off < dp->size; off += 512) {
+  for(off = 0; off < dp->size; off += BSIZE) {
-    bp = bread(dp->dev, bmap(dp, off / 512));
+    bp = bread(dp->dev, bmap(dp, off / BSIZE));
     for(ep = (struct dirent *) bp->data;
-	ep < (struct dirent *) (bp->data + 512);
+	ep < (struct dirent *) (bp->data + BSIZE);
 	ep++){
       if(ep->inum == 0) {
 	goto found;
@@ -304,7 +340,7 @@ mknod(struct inode *dp, char *cp, short type, short major, short minor)
  found:
   ep->inum = ip->inum;
   for(i = 0; i < DIRSIZ && cp[i]; i++) ep->name[i] = cp[i];
-  bwrite (dp->dev, bp, bmap(dp, off/512));   // write directory
+  bwrite (dp->dev, bp, bmap(dp, off/BSIZE));   // write directory
   brelse(bp);
   iupdate (ip);
   return ip;

fs.h

@@ -1,15 +1,16 @@
 // on-disk file system format
 
-// second sector
+#define BSIZE 512  // block size
+
+// sector 1 (2nd sector)
 struct superblock{
-  int nblocks;
+  uint size;
-  int ninodes;
+  uint nblocks;
+  uint ninodes;
 };
 
 #define NDIRECT 13
 
-// inodes start at the third sector
-// and blocks start at (ninodes * sizeof(dinode) + 511) / 512
 struct dinode {
   short type;
   short major;
@@ -23,7 +24,11 @@ struct dinode {
 #define T_FILE 2
 #define T_DEV 3
 
-#define IPB (512 / sizeof(struct dinode))
+// sector 0 is unused, sector 1 is superblock, inodes start at sector 2
+#define IPB (BSIZE / sizeof(struct dinode))
+#define IBLOCK(inum) (inum / IPB + 2)   // start of inode
+#define BPB (BSIZE*8)
+#define BBLOCK(b,ninodes) (b/BPB + (ninodes/IPB) + 3)  // start of bitmap
 
 #define DIRSIZ 14
 

mkfs.c

@@ -8,15 +8,19 @@
 #include "param.h"
 #include "fs.h"
 
-int nblocks = 1009;
+int nblocks = 1008;
 int ninodes = 100;
+int size = 1024;
 
 int fsfd;
 struct superblock sb;
 char zeroes[512];
 uint freeblock;
+uint usedblocks;
+uint bitblocks;
 uint freeinode = 1;
 
+void balloc(int);
 void wsect(uint, void *);
 void winode(uint, struct dinode *);
 void rsect(uint sec, void *buf);
@@ -67,12 +71,20 @@ main(int argc, char *argv[])
     exit(1);
   }
 
-  sb.nblocks = xint(nblocks); // so whole disk is 1024 sectors
+  sb.size = xint(size);
+  sb.nblocks = xint(nblocks); // so whole disk is size sectors
   sb.ninodes = xint(ninodes);
 
-  freeblock = ninodes / IPB + 2;
+  bitblocks = sb.size/(512*8) + 1; 
+  usedblocks = ninodes / IPB + 3 + bitblocks;
+  freeblock = usedblocks;
 
-  for(i = 0; i < nblocks + (ninodes / IPB) + 3; i++)
+  printf ("used %d (bit %d ninode %d) free %d total %d\n", usedblocks, 
+	  bitblocks, ninodes/IPB + 1, freeblock, nblocks+usedblocks);
+
+  assert (nblocks + usedblocks == size);
+
+  for(i = 0; i < nblocks + usedblocks; i++)
     wsect(i, zeroes);
 
   wsect(1, &sb);
@@ -110,6 +122,8 @@ main(int argc, char *argv[])
     close(fd);
   }
 
+  balloc(usedblocks);
+
   exit(0);
 }
 
@@ -186,6 +200,22 @@ ialloc(ushort type)
   return inum;
 }
 
+void
+balloc(int used)
+{
+  uchar buf[512];
+  int i;
+
+  printf("balloc: first %d blocks have been allocated\n", used);
+  assert (used < 512);
+  bzero(buf, 512);
+  for (i = 0; i < used; i++) {
+    buf[i/8] = buf[i/8] | (0x1 << (i%8));
+  }
+  printf("balloc: write bitmap block at sector %d\n", ninodes/IPB + 3);
+  wsect(ninodes / IPB + 3, buf);
+}
+
 #define min(a, b) ((a) < (b) ? (a) : (b))
 
 void
@@ -202,8 +232,10 @@ iappend(uint inum, void *xp, int n)
   while(n > 0){
     fbn = off / 512;
     assert(fbn < NDIRECT);
-    if(din.addrs[fbn] == 0)
+    if(din.addrs[fbn] == 0) {
       din.addrs[fbn] = xint(freeblock++);
+      usedblocks++;
+    }
     n1 = min(n, (fbn + 1) * 512 - off);
     rsect(xint(din.addrs[fbn]), buf);
     bcopy(p, buf + off - (fbn * 512), n1);