[PATCH] fs/minix: bugfix, number of indirect block ptrs per block depends on block size

[Erik van der Kouwe <vdkouwe@cs.vu.nl>]

From: Erik van der Kouwe <vdkouwe@cs.vu.nl>

The MINIX filesystem driver used a constant number of indirect block 
pointers in an indirect block. This worked only for filesystems with 1kb 
block, while the MINIX default block size is now 4kb. As a consequence, 
large files were read incorrectly on such filesystems and writing a 
large file would cause the filesystem to become corrupted. This patch 
computes the number of indirect block pointers based on the block size, 
making the driver work for each block size. 

I would like to thank Feiran Zheng ('Fam') for pointing out the cause 
of the corruption.

Signed-off-by: Erik van der Kouwe <vdkouwe@cs.vu.nl>
---

--- fs/minix/itree_v2.c.orig	2010-05-26 14:10:15.000000000 +0200
+++ fs/minix/itree_v2.c	2010-05-26 13:44:53.000000000 +0200
@@ -20,6 +20,9 @@ static inline block_t *i_data(struct ino
 	return (block_t *)minix_i(inode)->u.i2_data;
 }
 
+#define DIRCOUNT 7
+#define INDIRCOUNT(sb) ((sb)->s_blocksize / 4)
+
 static int block_to_path(struct inode * inode, long block, int offsets[DEPTH])
 {
 	int n = 0;
@@ -34,21 +37,21 @@ static int block_to_path(struct inode * 
 			printk("MINIX-fs: block_to_path: "
 			       "block %ld too big on dev %s\n",
 				block, bdevname(sb->s_bdev, b));
-	} else if (block < 7) {
+	} else if (block < DIRCOUNT) {
 		offsets[n++] = block;
-	} else if ((block -= 7) < 256) {
-		offsets[n++] = 7;
+	} else if ((block -= DIRCOUNT) < INDIRCOUNT(sb)) {
+		offsets[n++] = DIRCOUNT;
 		offsets[n++] = block;
-	} else if ((block -= 256) < 256*256) {
-		offsets[n++] = 8;
-		offsets[n++] = block>>8;
-		offsets[n++] = block & 255;
+	} else if ((block -= INDIRCOUNT(sb)) < INDIRCOUNT(sb) * INDIRCOUNT(sb)) {
+		offsets[n++] = DIRCOUNT + 1;
+		offsets[n++] = block / INDIRCOUNT(sb);
+		offsets[n++] = block % INDIRCOUNT(sb);
 	} else {
-		block -= 256*256;
-		offsets[n++] = 9;
-		offsets[n++] = block>>16;
-		offsets[n++] = (block>>8) & 255;
-		offsets[n++] = block & 255;
+		block -= INDIRCOUNT(sb) * INDIRCOUNT(sb);
+		offsets[n++] = DIRCOUNT + 2;
+		offsets[n++] = (block / INDIRCOUNT(sb)) / INDIRCOUNT(sb);
+		offsets[n++] = (block / INDIRCOUNT(sb)) % INDIRCOUNT(sb);
+		offsets[n++] = block % INDIRCOUNT(sb);
 	}
 	return n;
 }