Pick up where i left off in april:

- move log into metadata part of disk, so that marking
that the log's blocks are in use falls out for free
- superblock describes the whole disk (sizes and offets)
- sizes and offsets are computed in one place (mkfs) and
the rest of the code refers to the superblock for these values,
instead of recomputing them.

1 files changed, 11 insertions, 10 deletions

diff --git a/fs.h b/fs.h
index f191d43..e1d7d09 100644
--- a/fs.h
+++ b/fs.h
@@ -1,22 +1,23 @@
 // On-disk file system format. 
 // Both the kernel and user programs use this header file.
 
-// Block 0 is unused.
-// Block 1 is super block.
-// Blocks 2 through sb.ninodes/IPB hold inodes.
-// Then free bitmap blocks holding sb.size bits.
-// Then sb.nblocks data blocks.
-// Then sb.nlog log blocks.
 
 #define ROOTINO 1  // root i-number
 #define BSIZE 512  // block size
 
-// File system super block
+// Disk layout:
+// [ boot block | super block | log | inode blocks | free bit map | data blocks ]
+//
+// mkfs computes the super block and builds an initial file system. The super describes
+// the disk layout:
 struct superblock {
   uint size;         // Size of file system image (blocks)
   uint nblocks;      // Number of data blocks
   uint ninodes;      // Number of inodes.
   uint nlog;         // Number of log blocks
+  uint logstart;     // Block number of first log block
+  uint inodestart;   // Block number of first inode block
+  uint bmapstart;    // Block number of first free map block
 };
 
 #define NDIRECT 12
@@ -37,13 +38,13 @@ struct dinode {
 #define IPB           (BSIZE / sizeof(struct dinode))
 
 // Block containing inode i
-#define IBLOCK(i)     ((i) / IPB + 2)
+#define IBLOCK(i, sb)     ((i) / IPB + sb.inodestart)
 
 // Bitmap bits per block
 #define BPB           (BSIZE*8)
 
-// Block containing bit for block b
-#define BBLOCK(b, ninodes) (b/BPB + (ninodes)/IPB + 3)
+// Block of free map containing bit for block b
+#define BBLOCK(b, sb) (b/BPB + sb.bmapstart)
 
 // Directory is a file containing a sequence of dirent structures.
 #define DIRSIZ 14