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

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>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/minix/itree_v2.c b/fs/minix/itree_v2.c
index f2301096936923d3d17f01332484e7b2866e7b4f..13487ad168944e37eb8871161c3077d50b5a271c 100644 (file)
--- a/fs/minix/itree_v2.c
+++ b/fs/minix/itree_v2.c
@@ -20,6 +20,9 @@ static inline block_t *i_data(struct inode *inode)
        return (block_t *)minix_i(inode)->u.i2_data;
 }
 
+#define DIRCOUNT 7
+#define INDIRCOUNT(sb) (1 << ((sb)->s_blocksize_bits - 2))
+
 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 * inode, long block, int offsets[DEPTH])
                        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;
 }