[PATCH] dm: verity support data device offset

[Wesley Miaw]

I needed to add support for dm-verity with data that is offset into a block 
device. As part of this I found that the existing code did not compute the 
correct hash block index if the data_start might be non-zero. Here's a patch to 
add support for a data offset target parameter as well as a fix to the hash 
block index computation.

Patch and (hopefully proper) commit message below. Thanks.
--
Wesley Miaw

============================================================

Add data device start block index to dm-verity target parameters to support 
verity targets where the data does not begin at sector 0 of the block device. 
Also fix the hash block index computation so it takes into account data offsets.

---

--- a/drivers/md/dm-verity.c    2012-08-07 16:03:03.778759000 -0700
+++ b/drivers/md/dm-verity.c    2012-08-07 17:30:56.914569414 -0700
@@ -491,7 +491,7 @@
        io->bio = bio;
        io->orig_bi_end_io = bio->bi_end_io;
        io->orig_bi_private = bio->bi_private;
-       io->block = bio->bi_sector >> (v->data_dev_block_bits - SECTOR_SHIFT);
+       io->block = (bio->bi_sector - v->data_start)  >> 
(v->data_dev_block_bits - SECTOR_SHIFT);
        io->n_blocks = bio->bi_size >> v->data_dev_block_bits;
 
        bio->bi_end_io = verity_end_io;
@@ -641,6 +641,7 @@
  *     <hash device>
  *     <data block size>
  *     <hash block size>
+ *     <data start block>
  *     <the number of data blocks>
  *     <hash start block>
  *     <algorithm>
@@ -671,8 +672,8 @@
                goto bad;
        }
 
-       if (argc != 10) {
-               ti->error = "Invalid argument count: exactly 10 arguments 
required";
+       if (argc != 11) {
+               ti->error = "Invalid argument count: exactly 11 arguments 
required";
                r = -EINVAL;
                goto bad;
        }
@@ -718,6 +719,15 @@
        v->hash_dev_block_bits = ffs(num) - 1;
 
        if (sscanf(argv[5], "%llu%c", &num_ll, &dummy) != 1 ||
+               num_ll << (v->data_dev_block_bits - SECTOR_SHIFT) !=
+               (sector_t)num_ll << (v->data_dev_block_bits - SECTOR_SHIFT)) {
+               ti->error = "Invalid data start";
+               r = -EINVAL;
+               goto bad;
+       }
+       v->data_start = num_ll << (v->data_dev_block_bits - SECTOR_SHIFT);
+
+       if (sscanf(argv[6], "%llu%c", &num_ll, &dummy) != 1 ||
            num_ll << (v->data_dev_block_bits - SECTOR_SHIFT) !=
            (sector_t)num_ll << (v->data_dev_block_bits - SECTOR_SHIFT)) {
                ti->error = "Invalid data blocks";
@@ -732,7 +742,7 @@
                goto bad;
        }
 
-       if (sscanf(argv[6], "%llu%c", &num_ll, &dummy) != 1 ||
+       if (sscanf(argv[7], "%llu%c", &num_ll, &dummy) != 1 ||
            num_ll << (v->hash_dev_block_bits - SECTOR_SHIFT) !=
            (sector_t)num_ll << (v->hash_dev_block_bits - SECTOR_SHIFT)) {
                ti->error = "Invalid hash start";
@@ -741,7 +751,7 @@
        }
        v->hash_start = num_ll;
 
-       v->alg_name = kstrdup(argv[7], GFP_KERNEL);
+       v->alg_name = kstrdup(argv[8], GFP_KERNEL);
        if (!v->alg_name) {
                ti->error = "Cannot allocate algorithm name";
                r = -ENOMEM;
@@ -770,23 +780,23 @@
                r = -ENOMEM;
                goto bad;
        }
-       if (strlen(argv[8]) != v->digest_size * 2 ||
-           hex2bin(v->root_digest, argv[8], v->digest_size)) {
+       if (strlen(argv[9]) != v->digest_size * 2 ||
+           hex2bin(v->root_digest, argv[9], v->digest_size)) {
                ti->error = "Invalid root digest";
                r = -EINVAL;
                goto bad;
        }
 
-       if (strcmp(argv[9], "-")) {
-               v->salt_size = strlen(argv[9]) / 2;
+       if (strcmp(argv[10], "-")) {
+               v->salt_size = strlen(argv[10]) / 2;
                v->salt = kmalloc(v->salt_size, GFP_KERNEL);
                if (!v->salt) {
                        ti->error = "Cannot allocate salt";
                        r = -ENOMEM;
                        goto bad;
                }
-               if (strlen(argv[9]) != v->salt_size * 2 ||
-                   hex2bin(v->salt, argv[9], v->salt_size)) {
+               if (strlen(argv[10]) != v->salt_size * 2 ||
+                   hex2bin(v->salt, argv[10], v->salt_size)) {
                        ti->error = "Invalid salt";
                        r = -EINVAL;
                        goto bad;

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