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    SubjectRe: [PATCH] dm: remake of the verity target
    Mikulas Patocka (mpatocka@redhat.com) wrote:
    > Hi
    >
    > > Hi Mikulus,
    > >
    > > This is some nice work. I like that you've been able to abstract a lot
    > > of the hash buffer management with dm-bufio. You got rid of the I/O queue.
    > > I've been meaning to do that for a while. The prefetch is also nice.
    > > We planned to do this but I decided to not do it now in order to get the
    > > base functionality in:
    > >
    > > http://crosbug.com/25441
    > >
    > > However, there are some things that I don't like. I don't like comments
    > > either but you have none. You also removed our documentation. You are
    >
    > I added some comments. As for documentation, it's OK to use documentation

    Thanks.

    > from your patch because the on-disk format and the target arguments are
    > the same (with an enhancement that my code supports different data and
    > metadata bock size and it has variable-length salt).
    >

    Would you mind adding the documentation as part 2 of your series.

    > > allocated a complete shash_desc per I/O. We only allocate one per CPU.
    >
    > The hash of 4k block takes 174000 cycles. So trying to optimize
    > memory latency that is about 250 cycles doesn't make much sense.
    >
    > I actually observed better performance using verity on ramdisk with
    > workqueue unbound to specific CPUs. The reason is that the ramdisk bio
    > completion routine is always run on the same CPU (that one that submitted
    > the request), so with bound workqueue, everything was executing on one
    > CPU. With unbound workqueue, I got parallelism.
    >

    I guess it depends on whether you're CPU bound or I/O bound. If you're
    CPU-bound and all the schedule is doing a good job of keeping all the
    cores busy, then you're just adding extra cache misses. But if you're
    not CPU-bound, then you can parallelize the hashing. So I guess it
    depends. Anway, arguable which is better without data on real workloads.

    At some point, it would be interesting to compare ChromeOS boot performance
    with both approaches.


    > > We short-circuit the hash at any level. Your implementation can only
    > > shirt circuit at the lowest level.
    >
    > It short-circuits hash at all levels. If the function
    > "verity_verify_level" finds out that "aux->hash_verified" is non-zero, it
    > doesn't do any hashing, it just copies the hash for the lower level. My
    > implementation walks the tree from the top to the bottom, but it doesn't
    > do hash verification if the same block has been verified before.
    >

    I agree. Short-circuiting won't give an extra benefit. For some reason,
    I thought you might be re-verifying a node but that's not the case.

    > All this tree-walking from the root to the bottom is 50-times faster than
    > the actual hashing of the data block (I measured that), so there's not
    > much point in trying to optimize it. I did a simple optimization (don't
    > walk the tree if the lowest block is already verified) and I don't need to
    > do anything complicated given the fact that it can't improve more than by
    > 2%.
    >
    > > I'd like to propose that we get the version we sent upstream and then work
    > > together on adding some of your enhancements incrementally.
    >
    > If you add dm-bufio support, you end up deleting majority of the original
    > code anyway. That's why I wrote it from scratch and that's why I didn't
    > attempt to morph your code.
    >
    > It's simpler to write the code from scratch and it is also less bug-prone.
    >
    > > Other than
    > > the changes we've made to cleanup for upstreaming, the version I
    > > submitted is the code we are using in production.
    > >
    > > I'm happy to add prefetch now if that is required for merging.
    > >
    > > What do you think?
    > >
    > > Regards,
    > > Mandeep
    >
    > This is the version with comments added:
    >
    > Mikulas
    >
    > ----
    >
    > Remake of the google dm-verity patch.
    >
    > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    >

    Signed-off-by: Mandeep Singh Baines <msb@chromium.org>

    Nice work.

    I have a few nits but would be happy to see this merged. It doesn't
    look like the version I worked on will ever get merged, maybe you'll
    have better luck:)

    > ---
    > drivers/md/Kconfig | 17
    > drivers/md/Makefile | 1
    > drivers/md/dm-verity.c | 851 +++++++++++++++++++++++++++++++++++++++++++++++++
    > 3 files changed, 869 insertions(+)
    >
    > Index: linux-3.3-rc6-fast/drivers/md/Kconfig
    > ===================================================================
    > --- linux-3.3-rc6-fast.orig/drivers/md/Kconfig 2012-03-13 21:46:03.000000000 +0100
    > +++ linux-3.3-rc6-fast/drivers/md/Kconfig 2012-03-13 21:46:05.000000000 +0100
    > @@ -404,4 +404,21 @@ config DM_VERITY2
    >
    > If unsure, say N.
    >
    > +config DM_VERITY
    > + tristate "Verity target support"
    > + depends on BLK_DEV_DM
    > + select CRYPTO
    > + select CRYPTO_HASH
    > + select DM_BUFIO
    > + ---help---
    > + This device-mapper target allows you to create a device that
    > + transparently integrity checks the data on it. You'll need to
    > + activate the digests you're going to use in the cryptoapi
    > + configuration.
    > +
    > + To compile this code as a module, choose M here: the module will
    > + be called dm-verity.
    > +
    > + If unsure, say N.
    > +
    > endif # MD
    > Index: linux-3.3-rc6-fast/drivers/md/Makefile
    > ===================================================================
    > --- linux-3.3-rc6-fast.orig/drivers/md/Makefile 2012-03-13 21:46:03.000000000 +0100
    > +++ linux-3.3-rc6-fast/drivers/md/Makefile 2012-03-13 21:46:05.000000000 +0100
    > @@ -29,6 +29,7 @@ obj-$(CONFIG_MD_FAULTY) += faulty.o
    > obj-$(CONFIG_BLK_DEV_MD) += md-mod.o
    > obj-$(CONFIG_BLK_DEV_DM) += dm-mod.o
    > obj-$(CONFIG_DM_BUFIO) += dm-bufio.o
    > +obj-$(CONFIG_DM_VERITY) += dm-verity.o
    > obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
    > obj-$(CONFIG_DM_DELAY) += dm-delay.o
    > obj-$(CONFIG_DM_FLAKEY) += dm-flakey.o
    > Index: linux-3.3-rc6-fast/drivers/md/dm-verity.c
    > ===================================================================
    > --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    > +++ linux-3.3-rc6-fast/drivers/md/dm-verity.c 2012-03-13 22:02:05.000000000 +0100
    > @@ -0,0 +1,851 @@
    > +/*
    > + * Copyright (C) 2012 Red Hat, Inc.
    > + *
    > + * Author: Mikulas Patocka <mpatocka@redhat.com>
    > + *
    > + * Based on Chromium dm-verity driver (C) 2011 The Chromium OS Authors
    > + *
    > + * This file is released under the GPLv2.
    > + *
    > + * Device mapper target parameters:
    > + * <version> 0
    > + * <data device>
    > + * <hash device>
    > + * <hash start> (typically 0)
    > + * <block size> (typically 4096)
    > + * <algorithm>
    > + * <digest>
    > + * optional parameters:
    > + * <salt> (should have 32 bytes for compatibility with Google code)
    > + * <hash block size> (by default it is the same as data block size)
    > + *
    > + * In the file "/sys/module/dm_verity/parameters/prefetch_cluster" you can set
    > + * default prefetch value. Data are read in "prefetch_cluster" chunks from the
    > + * hash device. Prefetch cluster greatly improves performance when data and hash
    > + * are on the same disk on different partitions.
    > + */
    > +
    > +#include <linux/module.h>
    > +#include <linux/device-mapper.h>
    > +#include <crypto/hash.h>
    > +#include "dm-bufio.h"
    > +
    > +#define DM_MSG_PREFIX "verity"
    > +
    > +#define DM_VERITY_IO_VEC_INLINE 16
    > +#define DM_VERITY_MEMPOOL_SIZE 4
    > +#define DM_VERITY_DEFAULT_PREFETCH_SIZE 262144
    > +
    > +#define DM_VERITY_MAX_LEVELS 63
    > +
    > +static unsigned prefetch_cluster = DM_VERITY_DEFAULT_PREFETCH_SIZE;
    > +
    > +module_param_named(prefetch_cluster, prefetch_cluster, uint, S_IRUGO | S_IWUSR);
    > +
    > +struct dm_verity {
    > + struct dm_dev *data_dev;
    > + struct dm_dev *hash_dev;
    > + struct dm_target *ti;
    > + struct dm_bufio_client *bufio;
    > + char *alg_name;
    > + struct crypto_shash *tfm;
    > + u8 *root_digest; /* digest of the root block */
    > + u8 *salt; /* salt, its size is salt_size */
    > + unsigned salt_size;
    > + sector_t data_start; /* data offset in 512-byte sectors */
    > + sector_t hash_start; /* hash start in blocks */
    > + sector_t data_blocks; /* the number of data blocks */
    > + sector_t hash_blocks; /* the number of hash blocks */
    > + unsigned char data_dev_block_bits; /* log2(data blocksize) */
    > + unsigned char hash_dev_block_bits; /* log2(hash blocksize) */
    > + unsigned char hash_per_block_bits; /* log2(hashes in hash block) */
    > + unsigned char levels; /* the number of tree levels */
    > + unsigned digest_size; /* digest size for the current hash algorithm */
    > + unsigned shash_descsize;/* the size of temporary space for crypto */
    > +
    > + mempool_t *io_mempool; /* mempool of struct dm_verity_io */
    > + mempool_t *vec_mempool; /* mempool of bio vector */
    > +

    Since there are no writes, do we even need mempool? I was thinking of
    removing all mempools. I can't think of case where a mempool helps you
    for a read-only device. There is no reading under memory pressure.

    > + struct workqueue_struct *verify_wq;
    > +
    > + /* starting blocks for each tree level. 0 is the lowest level. */
    > + sector_t hash_level_block[DM_VERITY_MAX_LEVELS];
    > +};
    > +
    > +struct dm_verity_io {
    > + struct dm_verity *v;
    > + struct bio *bio;
    > +
    > + /* original values of bio->bi_end_io and bio->bi_private */
    > + bio_end_io_t *orig_bi_end_io;
    > + void *orig_bi_private;
    > +
    > + sector_t block;
    > + unsigned n_blocks;
    > +
    > + /* saved bio vector */
    > + struct bio_vec *io_vec;
    > + unsigned io_vec_size;
    > +
    > + struct work_struct work;
    > +
    > + /* a space for short vectors; longer vectors are allocated separately */
    > + struct bio_vec io_vec_inline[DM_VERITY_IO_VEC_INLINE];
    > +
    > + /* variable-size fields, accessible with functions
    > + io_hash_desc, io_real_digest, io_want_digest */
    > + /* u8 hash_desc[crypto_shash_descsize(v->tfm)]; */
    > + /* u8 real_digest[v->digest_size]; */
    > + /* u8 want_digest[v->digest_size]; */

    Nit. Commented code should be removed.

    > +};
    > +
    > +static struct shash_desc *io_hash_desc(struct dm_verity *v, struct dm_verity_io *io)
    > +{
    > + return (struct shash_desc *)(io + 1);
    > +}
    > +
    > +static u8 *io_real_digest(struct dm_verity *v, struct dm_verity_io *io)
    > +{
    > + return (u8 *)(io + 1) + v->shash_descsize;
    > +}
    > +
    > +static u8 *io_want_digest(struct dm_verity *v, struct dm_verity_io *io)
    > +{
    > + return (u8 *)(io + 1) + v->shash_descsize + v->digest_size;
    > +}
    > +
    > +/*
    > + * Auxiliary structure appended to each dm-bufio buffer. If the value
    > + * hash_verified is nonzero, hash of the block has been verified.
    > + *
    > + * There is no lock around this value, a race condition can at worst cause
    > + * that multiple processes verify the hash of the same buffer simultaneously.
    > + * This condition is harmless, so we don't need locking.
    > + */
    > +struct buffer_aux {
    > + int hash_verified;
    > +};
    > +
    > +/*
    > + * Initialize struct buffer_aux for a freshly created buffer.
    > + */
    > +static void dm_bufio_alloc_callback(struct dm_buffer *buf)
    > +{
    > + struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
    > + aux->hash_verified = 0;
    > +}
    > +
    > +/*
    > + * Translate input sector number to the sector number on the target device.
    > + */
    > +static sector_t verity_map_sector(struct dm_verity *v, sector_t bi_sector)
    > +{
    > + return v->data_start + dm_target_offset(v->ti, bi_sector);
    > +}
    > +
    > +/*
    > + * Return hash position of a specified block at a specified tree level
    > + * (0 is the lowest level).
    > + * The lowest "hash_per_block_bits"-bits of the result denote hash position
    > + * inside a hash block. The remaining bits denode location of the hash block.
    > + */
    > +static sector_t verity_position_at_level(struct dm_verity *v, sector_t block,
    > + int level)
    > +{
    > + return block >> (level * v->hash_per_block_bits);
    > +}
    > +
    > +static void verity_hash_at_level(struct dm_verity *v, sector_t block, int level,
    > + sector_t *hash_block, unsigned *offset)
    > +{
    > + sector_t position = verity_position_at_level(v, block, level);
    > +
    > + *hash_block = v->hash_level_block[level] + (position >> v->hash_per_block_bits);
    > + if (offset)
    > + *offset = v->digest_size * (position & ((1 << v->hash_per_block_bits) - 1));
    > +}
    > +
    > +/*
    > + * Verify hash of a metadata block pertaining to the specified data block
    > + * ("block" argument) at a specified level ("level" argument).
    > + *
    > + * On successful return, io_want_digest(v, io) contains the hash value for
    > + * a lower tree level or for the data block (if we're at the lowest leve).
    > + *
    > + * If "skip_unverified" is true, unverified buffer is skipped an 1 is returned.
    > + * If "skip_unverified" is false, unverified buffer is hashed and verified
    > + * against current value of io_want_digest(v, io).
    > + */
    > +static int verity_verify_level(struct dm_verity_io *io, sector_t block,
    > + int level, bool skip_unverified)
    > +{
    > + struct dm_verity *v = io->v;
    > + struct dm_buffer *buf;
    > + struct buffer_aux *aux;
    > + u8 *data;
    > + int r;
    > + sector_t hash_block;
    > + unsigned offset;
    > +
    > + verity_hash_at_level(v, block, level, &hash_block, &offset);
    > +
    > + data = dm_bufio_read(v->bufio, hash_block, &buf);
    > + if (unlikely(IS_ERR(data)))
    > + return PTR_ERR(data);
    > +
    > + aux = dm_bufio_get_aux_data(buf);
    > +
    > + if (!aux->hash_verified) {
    > + struct shash_desc *desc;
    > + u8 *result;
    > +
    > + if (skip_unverified) {
    > + r = 1;
    > + goto release_ret_r;
    > + }
    > +
    > + desc = io_hash_desc(v, io);
    > + desc->tfm = v->tfm;
    > + desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
    > + r = crypto_shash_init(desc);
    > + if (r < 0) {
    > + DMERR("crypto_shash_init failed: %d", r);
    > + goto release_ret_r;
    > + }
    > +
    > + r = crypto_shash_update(desc, data, 1 << v->hash_dev_block_bits);
    > + if (r < 0) {
    > + DMERR("crypto_shash_update failed: %d", r);
    > + goto release_ret_r;
    > + }
    > +
    > + r = crypto_shash_update(desc, v->salt, v->salt_size);
    > + if (r < 0) {
    > + DMERR("crypto_shash_update failed: %d", r);
    > + goto release_ret_r;
    > + }
    > +
    > + result = io_real_digest(v, io);
    > + r = crypto_shash_final(desc, result);
    > + if (r < 0) {
    > + DMERR("crypto_shash_final failed: %d", r);
    > + goto release_ret_r;
    > + }
    > + if (unlikely(memcmp(result, io_want_digest(v, io), v->digest_size))) {
    > + DMERR_LIMIT("metadata block %llu is corrupted",
    > + (unsigned long long)hash_block);
    > + r = -EIO;
    > + goto release_ret_r;
    > + } else
    > + aux->hash_verified = 1;
    > + }
    > +
    > + data += offset;
    > +
    > + memcpy(io_want_digest(v, io), data, v->digest_size);
    > +
    > + dm_bufio_release(buf);
    > + return 0;
    > +
    > +release_ret_r:
    > + dm_bufio_release(buf);
    > + return r;
    > +}
    > +
    > +/*
    > + * Verify one "dm_verity_io" structure.
    > + */
    > +static int verity_verify_io(struct dm_verity_io *io)
    > +{
    > + struct dm_verity *v = io->v;
    > + unsigned b;
    > + int i;
    > + unsigned vector = 0, offset = 0;
    > + for (b = 0; b < io->n_blocks; b++) {
    > + struct shash_desc *desc;
    > + u8 *result;
    > + int r;
    > + unsigned todo;
    > +
    > + if (likely(v->levels)) {
    > + /*
    > + * First, we try to get the requested hash for
    > + * the current block. If the hash block itself is
    > + * verified, zero is returned. If it isn't, this
    > + * function returns 0 and we fall back to whole
    > + * chain verification.
    > + */
    > + int r = verity_verify_level(io, io->block + b, 0, true);
    > + if (likely(!r))
    > + goto test_block_hash;
    > + if (r < 0)
    > + return r;
    > + }
    > +
    > + memcpy(io_want_digest(v, io), v->root_digest, v->digest_size);
    > +
    > + for (i = v->levels - 1; i >= 0; i--) {
    > + int r = verity_verify_level(io, io->block + b, i, false);
    > + if (unlikely(r))
    > + return r;
    > + }
    > +
    > +test_block_hash:
    > + desc = io_hash_desc(v, io);
    > + desc->tfm = v->tfm;
    > + desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
    > + r = crypto_shash_init(desc);
    > + if (r < 0) {
    > + DMERR("crypto_shash_init failed: %d", r);
    > + return r;
    > + }
    > +
    > + todo = 1 << v->data_dev_block_bits;
    > + do {
    > + struct bio_vec *bv;
    > + u8 *page;
    > + unsigned len;
    > +
    > + BUG_ON(vector >= io->io_vec_size);
    > + bv = &io->io_vec[vector];
    > + page = kmap_atomic(bv->bv_page, KM_USER0);
    > + len = bv->bv_len - offset;
    > + if (likely(len >= todo))
    > + len = todo;
    > + r = crypto_shash_update(desc,
    > + page + bv->bv_offset + offset, len);
    > + kunmap_atomic(page, KM_USER0);
    > + if (r < 0) {
    > + DMERR("crypto_shash_update failed: %d", r);
    > + return r;
    > + }
    > + offset += len;
    > + if (likely(offset == bv->bv_len)) {
    > + offset = 0;
    > + vector++;
    > + }
    > + todo -= len;
    > + } while (todo);
    > +
    > + r = crypto_shash_update(desc, v->salt, v->salt_size);
    > + if (r < 0) {
    > + DMERR("crypto_shash_update failed: %d", r);
    > + return r;
    > + }
    > +
    > + result = io_real_digest(v, io);
    > + r = crypto_shash_final(desc, result);
    > + if (r < 0) {
    > + DMERR("crypto_shash_final failed: %d", r);
    > + return r;
    > + }
    > + if (unlikely(memcmp(result, io_want_digest(v, io), v->digest_size))) {
    > + DMERR_LIMIT("data block %llu is corrupted",
    > + (unsigned long long)(io->block + b));
    > + return -EIO;
    > + }
    > + }
    > + BUG_ON(vector != io->io_vec_size);
    > + BUG_ON(offset);
    > + return 0;
    > +}
    > +
    > +/*
    > + * End one "io" structure with a given error.
    > + */
    > +static void verity_finish_io(struct dm_verity_io *io, int error)
    > +{
    > + struct bio *bio = io->bio;
    > + struct dm_verity *v = io->v;
    > +
    > + bio->bi_end_io = io->orig_bi_end_io;
    > + bio->bi_private = io->orig_bi_private;
    > +
    > + if (io->io_vec != io->io_vec_inline)
    > + mempool_free(io->io_vec, v->vec_mempool);
    > + mempool_free(io, v->io_mempool);
    > +
    > + bio_endio(bio, error);
    > +}
    > +
    > +static void verity_work(struct work_struct *w)
    > +{
    > + struct dm_verity_io *io = container_of(w, struct dm_verity_io, work);
    > +
    > + verity_finish_io(io, verity_verify_io(io));
    > +}
    > +
    > +static void verity_end_io(struct bio *bio, int error)
    > +{
    > + struct dm_verity_io *io = bio->bi_private;
    > + if (error) {
    > + verity_finish_io(io, error);
    > + return;
    > + }
    > +
    > + INIT_WORK(&io->work, verity_work);
    > + queue_work(io->v->verify_wq, &io->work);
    > +}
    > +
    > +/*
    > + * Prefetch buffers for the specified io.
    > + * The root buffer is not prefetched, it is assumed that it will be cached
    > + * all the time.
    > + */
    > +static void verity_prefetch_io(struct dm_verity *v, struct dm_verity_io *io)
    > +{
    > + int i;
    > + for (i = v->levels - 2; i >= 0; i--) {
    > + sector_t hash_block_start;
    > + sector_t hash_block_end;
    > + verity_hash_at_level(v, io->block, i, &hash_block_start, NULL);
    > + verity_hash_at_level(v, io->block + io->n_blocks - 1, i, &hash_block_end, NULL);
    > + if (!i) {
    > + unsigned cluster = prefetch_cluster;
    > + /* barrier to stop GCC from re-reading prefetch_cluster again */
    > + barrier();
    > + cluster >>= v->data_dev_block_bits;
    > + if (unlikely(!cluster))
    > + goto no_prefetch_cluster;
    > + if (unlikely(cluster & (cluster - 1)))
    > + cluster = 1 << (fls(cluster) - 1);
    > +
    > + hash_block_start &= ~(sector_t)(cluster - 1);
    > + hash_block_end |= cluster - 1;
    > + if (unlikely(hash_block_end >= v->hash_blocks))
    > + hash_block_end = v->hash_blocks - 1;
    > + }
    > +no_prefetch_cluster:
    > + dm_bufio_prefetch(v->bufio, hash_block_start,
    > + hash_block_end - hash_block_start + 1);
    > + }
    > +}
    > +
    > +/*
    > + * Bio map function. It allocates dm_verity_io structure and bio vector and
    > + * fills them. Then it issues prefetches and the I/O.
    > + */
    > +static int verity_map(struct dm_target *ti, struct bio *bio,
    > + union map_info *map_context)
    > +{
    > + struct dm_verity *v = ti->private;
    > + struct dm_verity_io *io;
    > +
    > + if (((unsigned)bio->bi_sector | bio_sectors(bio)) &
    > + ((1 << (v->data_dev_block_bits - SECTOR_SHIFT)) - 1)) {
    > + DMERR_LIMIT("unaligned io");
    > + return -EIO;
    > + }
    > +
    > + if ((bio->bi_sector + bio_sectors(bio)) >>
    > + (v->data_dev_block_bits - SECTOR_SHIFT) > v->data_blocks) {
    > + DMERR_LIMIT("io out of range");
    > + return -EIO;
    > + }
    > +
    > + if (bio_data_dir(bio) == WRITE)
    > + return -EIO;
    > +
    > + io = mempool_alloc(v->io_mempool, GFP_NOIO);
    > + io->v = v;
    > + 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->n_blocks = bio->bi_size >> v->data_dev_block_bits;
    > +
    > + bio->bi_end_io = verity_end_io;
    > + bio->bi_private = io;
    > + bio->bi_bdev = v->data_dev->bdev;
    > + bio->bi_sector = verity_map_sector(v, bio->bi_sector);
    > +
    > + io->io_vec_size = bio->bi_vcnt - bio->bi_idx;
    > + if (io->io_vec_size < DM_VERITY_IO_VEC_INLINE)
    > + io->io_vec = io->io_vec_inline;
    > + else
    > + io->io_vec = mempool_alloc(v->vec_mempool, GFP_NOIO);
    > + memcpy(io->io_vec, bio_iovec(bio),
    > + io->io_vec_size * sizeof(struct bio_vec));
    > +
    > + verity_prefetch_io(v, io);
    > +
    > + generic_make_request(bio);
    > +
    > + return DM_MAPIO_SUBMITTED;
    > +}
    > +
    > +static int verity_status(struct dm_target *ti, status_type_t type,
    > + char *result, unsigned maxlen)
    > +{
    > + struct dm_verity *v = ti->private;
    > + unsigned sz = 0;
    > + unsigned x;
    > +
    > + switch (type) {
    > + case STATUSTYPE_INFO:
    > + result[0] = 0;
    > + break;
    > + case STATUSTYPE_TABLE:
    > + DMEMIT("%u %s %s %llu %u %s ",
    > + 0,
    > + v->data_dev->name,
    > + v->hash_dev->name,
    > + (unsigned long long)v->hash_start << (v->hash_dev_block_bits - SECTOR_SHIFT),
    > + 1 << v->data_dev_block_bits,
    > + v->alg_name
    > + );
    > + for (x = 0; x < v->digest_size; x++)
    > + DMEMIT("%02x", v->root_digest[x]);
    > + DMEMIT(" ");
    > + if (!v->salt_size)
    > + DMEMIT("-");
    > + else
    > + for (x = 0; x < v->salt_size; x++)
    > + DMEMIT("%02x", v->salt[x]);
    > + if (v->data_dev_block_bits != v->hash_dev_block_bits)
    > + DMEMIT(" %u", 1 << v->hash_dev_block_bits);
    > + break;
    > + }
    > + return 0;
    > +}
    > +
    > +static int verity_ioctl(struct dm_target *ti, unsigned cmd,
    > + unsigned long arg)
    > +{
    > + struct dm_verity *v = ti->private;
    > + int r = 0;
    > +
    > + if (v->data_start ||
    > + ti->len != i_size_read(v->data_dev->bdev->bd_inode) >> SECTOR_SHIFT)
    > + r = scsi_verify_blk_ioctl(NULL, cmd);
    > +
    > + return r ? : __blkdev_driver_ioctl(v->data_dev->bdev, v->data_dev->mode,
    > + cmd, arg);
    > +}
    > +
    > +static int verity_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
    > + struct bio_vec *biovec, int max_size)
    > +{
    > + struct dm_verity *v = ti->private;
    > + struct request_queue *q = bdev_get_queue(v->data_dev->bdev);
    > +
    > + if (!q->merge_bvec_fn)
    > + return max_size;
    > +
    > + bvm->bi_bdev = v->data_dev->bdev;
    > + bvm->bi_sector = verity_map_sector(v, bvm->bi_sector);
    > +
    > + return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
    > +}
    > +
    > +static int verity_iterate_devices(struct dm_target *ti,
    > + iterate_devices_callout_fn fn, void *data)
    > +{
    > + struct dm_verity *v = ti->private;
    > + return fn(ti, v->data_dev, v->data_start, ti->len, data);
    > +}
    > +
    > +static void verity_io_hints(struct dm_target *ti, struct queue_limits *limits)
    > +{
    > + struct dm_verity *v = ti->private;
    > +
    > + if (limits->logical_block_size < 1 << v->data_dev_block_bits)
    > + limits->logical_block_size = 1 << v->data_dev_block_bits;
    > + if (limits->physical_block_size < 1 << v->data_dev_block_bits)
    > + limits->physical_block_size = 1 << v->data_dev_block_bits;
    > + blk_limits_io_min(limits, limits->logical_block_size);
    > +}
    > +
    > +static void verity_dtr(struct dm_target *ti);
    > +
    > +static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
    > +{
    > + struct dm_verity *v;
    > + unsigned num;
    > + unsigned long long hs;
    > + int r;
    > + int i;
    > + sector_t hash_position;
    > + char dummy;
    > +
    > + v = kzalloc(sizeof(struct dm_verity), GFP_KERNEL);
    > + if (!v) {
    > + ti->error = "Cannot allocate verity structure";
    > + return -ENOMEM;
    > + }
    > + ti->private = v;
    > + v->ti = ti;
    > +
    > + if ((dm_table_get_mode(ti->table) & ~FMODE_READ) != 0) {
    > + ti->error = "Device must be readonly";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + if (argc < 7) {
    > + ti->error = "Not enough arguments";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + if (sscanf(argv[0], "%d%c", &num, &dummy) != 1 ||
    > + num != 0) {
    > + ti->error = "Invalid version";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + r = dm_get_device(ti, argv[1], FMODE_READ, &v->data_dev);
    > + if (r) {
    > + ti->error = "Data device lookup failed";
    > + goto bad;
    > + }
    > +
    > + r = dm_get_device(ti, argv[2], FMODE_READ, &v->hash_dev);
    > + if (r) {
    > + ti->error = "Data device lookup failed";
    > + goto bad;
    > + }
    > +
    > + if (sscanf(argv[3], "%llu%c", &hs, &dummy) != 1 ||
    > + hs != (sector_t)hs) {
    > + ti->error = "Invalid hash start";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + if (sscanf(argv[4], "%u%c", &num, &dummy) != 1 ||
    > + !num || (num & (num - 1)) ||
    > + num < bdev_logical_block_size(v->data_dev->bdev) ||
    > + num > PAGE_SIZE) {
    > + ti->error = "Invalid data device block size";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > + v->data_dev_block_bits = ffs(num) - 1;
    > + v->hash_dev_block_bits = ffs(num) - 1;
    > +
    > + v->alg_name = kstrdup(argv[5], GFP_KERNEL);
    > + if (!v->alg_name) {
    > + ti->error = "Cannot allocate algorithm name";
    > + r = -ENOMEM;
    > + goto bad;
    > + }
    > +
    > + v->tfm = crypto_alloc_shash(v->alg_name, 0, 0);
    > + if (IS_ERR(v->tfm)) {
    > + ti->error = "Cannot initialize hash function";
    > + r = PTR_ERR(v->tfm);
    > + v->tfm = NULL;
    > + goto bad;
    > + }
    > + v->digest_size = crypto_shash_digestsize(v->tfm);
    > + if ((1 << v->hash_dev_block_bits) < v->digest_size * 2) {
    > + ti->error = "Digest size too big";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > + v->shash_descsize =
    > + sizeof(struct shash_desc) + crypto_shash_descsize(v->tfm);
    > +
    > + v->root_digest = kmalloc(v->digest_size, GFP_KERNEL);
    > + if (!v->root_digest) {
    > + ti->error = "Cannot allocate root digest";
    > + r = -ENOMEM;
    > + goto bad;
    > + }
    > + if (strlen(argv[6]) != v->digest_size * 2 ||
    > + hex2bin(v->root_digest, argv[6], v->digest_size)) {
    > + ti->error = "Invalid root digest";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + if (argc > 7 && strcmp(argv[7], "-")) {
    > + v->salt_size = strlen(argv[7]) / 2;
    > + v->salt = kmalloc(v->salt_size, GFP_KERNEL);
    > + if (!v->salt) {
    > + ti->error = "Cannot allocate salt";
    > + r = -ENOMEM;
    > + goto bad;
    > + }
    > + if (strlen(argv[7]) != v->salt_size * 2 ||
    > + hex2bin(v->salt, argv[7], v->salt_size)) {
    > + ti->error = "Invalid salt";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > + }
    > +
    > + if (argc > 8) {
    > + if (sscanf(argv[8], "%u%c", &num, &dummy) != 1 ||
    > + !num || (num & (num - 1)) ||
    > + num < bdev_logical_block_size(v->hash_dev->bdev) ||
    > + num > INT_MAX) {
    > + ti->error = "Invalid hash device block size";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > + v->hash_dev_block_bits = ffs(num) - 1;
    > + }
    > +
    > + if (hs & ((1 << (v->hash_dev_block_bits - SECTOR_SHIFT)) - 1)) {
    > + ti->error = "Hash start not aligned on block boundary";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > + v->hash_start = hs >> (v->hash_dev_block_bits - SECTOR_SHIFT);
    > +
    > + if (ti->len > i_size_read(v->data_dev->bdev->bd_inode) >> SECTOR_SHIFT) {
    > + ti->error = "Data device si too small";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + if (ti->len & ((1 << (v->data_dev_block_bits - SECTOR_SHIFT)) - 1)) {
    > + ti->error = "Data device length is not aligned to block size";
    > + r = -EINVAL;
    > + goto bad;
    > + }
    > +
    > + v->data_blocks = ti->len >> (v->data_dev_block_bits - SECTOR_SHIFT);
    > +
    > + v->hash_per_block_bits =
    > + fls((1 << v->hash_dev_block_bits) / v->digest_size) - 1;
    > +
    > + v->levels = 0;
    > + if (v->data_blocks)
    > + while (v->hash_per_block_bits * v->levels < 64 &&
    > + (unsigned long long)(v->data_blocks - 1) >>
    > + (v->hash_per_block_bits * v->levels))
    > + v->levels++;
    > +
    > + if (v->levels > DM_VERITY_MAX_LEVELS) {
    > + ti->error = "Too many tree levels";
    > + r = -E2BIG;
    > + goto bad;
    > + }
    > +
    > + hash_position = v->hash_start;
    > + for (i = v->levels - 1; i >= 0; i--) {
    > + sector_t s;
    > + v->hash_level_block[i] = hash_position;
    > + s = verity_position_at_level(v, v->data_blocks, i);
    > + s = (s >> v->hash_per_block_bits) +
    > + !!(s & ((1 << v->hash_per_block_bits) - 1));
    > + if (hash_position + s < hash_position) {
    > + ti->error = "Hash device offset overflow";
    > + r = -E2BIG;
    > + goto bad;
    > + }
    > + hash_position += s;
    > + }
    > + v->hash_blocks = hash_position;
    > +
    > + v->bufio = dm_bufio_client_create(v->hash_dev->bdev,
    > + 1 << v->hash_dev_block_bits, 1, sizeof(struct buffer_aux),
    > + dm_bufio_alloc_callback, NULL);
    > + if (IS_ERR(v->bufio)) {
    > + ti->error = "Cannot initialize dm-bufio";
    > + r = PTR_ERR(v->bufio);
    > + v->bufio = NULL;
    > + goto bad;
    > + }
    > +
    > + if (dm_bufio_get_device_size(v->bufio) < v->hash_blocks) {
    > + ti->error = "Hash device is too small";
    > + r = -E2BIG;
    > + goto bad;
    > + }
    > +
    > + v->io_mempool = mempool_create_kmalloc_pool(DM_VERITY_MEMPOOL_SIZE,
    > + sizeof(struct dm_verity_io) + v->shash_descsize + v->digest_size * 2);
    > + if (!v->io_mempool) {
    > + ti->error = "Cannot allocate io mempool";
    > + r = -ENOMEM;
    > + goto bad;
    > + }
    > +
    > + v->vec_mempool = mempool_create_kmalloc_pool(DM_VERITY_MEMPOOL_SIZE,
    > + BIO_MAX_PAGES * sizeof(struct bio_vec));
    > + if (!v->vec_mempool) {
    > + ti->error = "Cannot allocate vector mempool";
    > + r = -ENOMEM;
    > + goto bad;
    > + }
    > +
    > + /*v->verify_wq = alloc_workqueue("verityd", WQ_CPU_INTENSIVE | WQ_MEM_RECLAIM, 1);*/
    > + /* WQ_UNBOUND greatly improves performance when running on ramdisk */
    > + v->verify_wq = alloc_workqueue("verityd", WQ_CPU_INTENSIVE | WQ_MEM_RECLAIM | WQ_UNBOUND, num_online_cpus());
    > + if (!v->verify_wq) {
    > + ti->error = "Cannot allocate workqueue";
    > + r = -ENOMEM;
    > + goto bad;
    > + }
    > +
    > + return 0;
    > +
    > +bad:
    > + verity_dtr(ti);
    > + return r;
    > +}
    > +
    > +static void verity_dtr(struct dm_target *ti)
    > +{
    > + struct dm_verity *v = ti->private;
    > +
    > + if (v->verify_wq)
    > + destroy_workqueue(v->verify_wq);
    > + if (v->vec_mempool)
    > + mempool_destroy(v->vec_mempool);
    > + if (v->io_mempool)
    > + mempool_destroy(v->io_mempool);
    > + if (v->bufio)
    > + dm_bufio_client_destroy(v->bufio);
    > + kfree(v->salt);
    > + kfree(v->root_digest);
    > + if (v->tfm)
    > + crypto_free_shash(v->tfm);
    > + kfree(v->alg_name);
    > + if (v->hash_dev)
    > + dm_put_device(ti, v->hash_dev);
    > + if (v->data_dev)
    > + dm_put_device(ti, v->data_dev);
    > + kfree(v);
    > +}
    > +
    > +static struct target_type verity_target = {
    > + .name = "verity",
    > + .version = {1, 0, 0},
    > + .module = THIS_MODULE,
    > + .ctr = verity_ctr,
    > + .dtr = verity_dtr,
    > + .map = verity_map,
    > + .status = verity_status,
    > + .ioctl = verity_ioctl,
    > + .merge = verity_merge,
    > + .iterate_devices = verity_iterate_devices,
    > + .io_hints = verity_io_hints,
    > +};
    > +
    > +static int __init dm_verity_init(void)
    > +{
    > + int r;
    > + r = dm_register_target(&verity_target);
    > + if (r < 0)
    > + DMERR("register failed %d", r);
    > + return r;
    > +}
    > +
    > +static void __exit dm_verity_exit(void)
    > +{
    > + dm_unregister_target(&verity_target);
    > +}
    > +
    > +module_init(dm_verity_init);
    > +module_exit(dm_verity_exit);
    > +
    > +MODULE_AUTHOR("Mikulas Patocka <mpatocka@redhat.com>");
    > +MODULE_DESCRIPTION(DM_NAME " target for transparent disk integrity checking");
    > +MODULE_LICENSE("GPL");
    > +
    > Index: linux-3.3-rc6-fast/drivers/md/dm-bufio.c
    > ===================================================================
    > --- linux-3.3-rc6-fast.orig/drivers/md/dm-bufio.c 2012-03-12 22:43:23.000000000 +0100
    > +++ linux-3.3-rc6-fast/drivers/md/dm-bufio.c 2012-03-13 15:41:02.000000000 +0100
    > @@ -579,7 +579,7 @@ static void write_endio(struct bio *bio,
    > struct dm_buffer *b = container_of(bio, struct dm_buffer, bio);
    >
    > b->write_error = error;
    > - if (error) {
    > + if (unlikely(error)) {
    > struct dm_bufio_client *c = b->c;
    > (void)cmpxchg(&c->async_write_error, 0, error);
    > }
    > @@ -698,13 +698,20 @@ static void __wait_for_free_buffer(struc
    > dm_bufio_lock(c);
    > }
    >
    > +enum new_flag {
    > + NF_FRESH = 0,
    > + NF_READ = 1,
    > + NF_GET = 2,
    > + NF_PREFETCH = 3
    > +};
    > +
    > /*
    > * Allocate a new buffer. If the allocation is not possible, wait until
    > * some other thread frees a buffer.
    > *
    > * May drop the lock and regain it.
    > */
    > -static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c)
    > +static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
    > {
    > struct dm_buffer *b;
    >
    > @@ -727,6 +734,9 @@ static struct dm_buffer *__alloc_buffer_
    > return b;
    > }
    >
    > + if (nf == NF_PREFETCH)
    > + return NULL;
    > +
    > if (!list_empty(&c->reserved_buffers)) {
    > b = list_entry(c->reserved_buffers.next,
    > struct dm_buffer, lru_list);
    > @@ -744,9 +754,12 @@ static struct dm_buffer *__alloc_buffer_
    > }
    > }
    >
    > -static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c)
    > +static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c, enum new_flag nf)
    > {
    > - struct dm_buffer *b = __alloc_buffer_wait_no_callback(c);
    > + struct dm_buffer *b = __alloc_buffer_wait_no_callback(c, nf);
    > +
    > + if (!b)
    > + return NULL;
    >
    > if (c->alloc_callback)
    > c->alloc_callback(b);
    > @@ -866,15 +879,8 @@ static struct dm_buffer *__find(struct d
    > * Getting a buffer
    > *--------------------------------------------------------------*/
    >
    > -enum new_flag {
    > - NF_FRESH = 0,
    > - NF_READ = 1,
    > - NF_GET = 2
    > -};
    > -
    > static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
    > - enum new_flag nf, struct dm_buffer **bp,
    > - int *need_submit)
    > + enum new_flag nf, int *need_submit)
    > {
    > struct dm_buffer *b, *new_b = NULL;
    >
    > @@ -882,6 +888,19 @@ static struct dm_buffer *__bufio_new(str
    >
    > b = __find(c, block);
    > if (b) {
    > +found_buffer:
    > + if (nf == NF_PREFETCH)
    > + return NULL;
    > + /*
    > + * Note: it is essential that we don't wait for the buffer to be
    > + * read if dm_bufio_get function is used. Both dm_bufio_get and
    > + * dm_bufio_prefetch can be used in the driver request routine.
    > + * If the user called both dm_bufio_prefetch and dm_bufio_get on
    > + * the same buffer, it would deadlock if we waited.
    > + */
    > + if (nf == NF_GET && unlikely(test_bit(B_READING, &b->state)))
    > + return NULL;
    > +
    > b->hold_count++;
    > __relink_lru(b, test_bit(B_DIRTY, &b->state) ||
    > test_bit(B_WRITING, &b->state));
    > @@ -891,7 +910,9 @@ static struct dm_buffer *__bufio_new(str
    > if (nf == NF_GET)
    > return NULL;
    >
    > - new_b = __alloc_buffer_wait(c);
    > + new_b = __alloc_buffer_wait(c, nf);
    > + if (!new_b)
    > + return NULL;
    >
    > /*
    > * We've had a period where the mutex was unlocked, so need to
    > @@ -900,10 +921,7 @@ static struct dm_buffer *__bufio_new(str
    > b = __find(c, block);
    > if (b) {
    > __free_buffer_wake(new_b);
    > - b->hold_count++;
    > - __relink_lru(b, test_bit(B_DIRTY, &b->state) ||
    > - test_bit(B_WRITING, &b->state));
    > - return b;
    > + goto found_buffer;
    > }
    >
    > __check_watermark(c);
    > @@ -957,7 +975,7 @@ static void *new_read(struct dm_bufio_cl
    > struct dm_buffer *b;
    >
    > dm_bufio_lock(c);
    > - b = __bufio_new(c, block, nf, bp, &need_submit);
    > + b = __bufio_new(c, block, nf, &need_submit);
    > dm_bufio_unlock(c);
    >
    > if (!b || IS_ERR(b))
    > @@ -1006,13 +1024,46 @@ void *dm_bufio_new(struct dm_bufio_clien
    > }
    > EXPORT_SYMBOL_GPL(dm_bufio_new);
    >
    > +void dm_bufio_prefetch(struct dm_bufio_client *c,
    > + sector_t block, unsigned n_blocks)
    > +{
    > + struct blk_plug plug;
    > +
    > + blk_start_plug(&plug);
    > + dm_bufio_lock(c);
    > +
    > + for (; n_blocks--; block++) {
    > + int need_submit;
    > + struct dm_buffer *b;
    > + b = __bufio_new(c, block, NF_PREFETCH, &need_submit);
    > + if (unlikely(b != NULL)) {
    > + dm_bufio_unlock(c);
    > +
    > + if (need_submit)
    > + submit_io(b, READ, b->block, read_endio);
    > + dm_bufio_release(b);
    > +
    > + dm_bufio_cond_resched();
    > +
    > + if (!n_blocks)
    > + goto flush_plug;
    > + dm_bufio_lock(c);
    > + }
    > +
    > + }
    > +
    > + dm_bufio_unlock(c);
    > +flush_plug:
    > + blk_finish_plug(&plug);
    > +}
    > +EXPORT_SYMBOL_GPL(dm_bufio_prefetch);
    > +
    > void dm_bufio_release(struct dm_buffer *b)
    > {
    > struct dm_bufio_client *c = b->c;
    >
    > dm_bufio_lock(c);
    >
    > - BUG_ON(test_bit(B_READING, &b->state));
    > BUG_ON(!b->hold_count);
    >
    > b->hold_count--;
    > @@ -1025,6 +1076,7 @@ void dm_bufio_release(struct dm_buffer *
    > * invalid buffer.
    > */
    > if ((b->read_error || b->write_error) &&
    > + !test_bit(B_READING, &b->state) &&
    > !test_bit(B_WRITING, &b->state) &&
    > !test_bit(B_DIRTY, &b->state)) {
    > __unlink_buffer(b);
    > @@ -1042,6 +1094,8 @@ void dm_bufio_mark_buffer_dirty(struct d
    >
    > dm_bufio_lock(c);
    >
    > + BUG_ON(test_bit(B_READING, &b->state));
    > +
    > if (!test_and_set_bit(B_DIRTY, &b->state))
    > __relink_lru(b, LIST_DIRTY);
    >
    > Index: linux-3.3-rc6-fast/drivers/md/dm-bufio.h
    > ===================================================================
    > --- linux-3.3-rc6-fast.orig/drivers/md/dm-bufio.h 2012-03-12 22:43:23.000000000 +0100
    > +++ linux-3.3-rc6-fast/drivers/md/dm-bufio.h 2012-03-12 22:43:25.000000000 +0100
    > @@ -63,6 +63,14 @@ void *dm_bufio_new(struct dm_bufio_clien
    > struct dm_buffer **bp);
    >
    > /*
    > + * Prefetch the specified blocks to the cache.
    > + * The function starts to read the blocks and returns without waiting for
    > + * I/O to finish.
    > + */
    > +void dm_bufio_prefetch(struct dm_bufio_client *c,
    > + sector_t block, unsigned n_blocks);
    > +
    > +/*
    > * Release a reference obtained with dm_bufio_{read,get,new}. The data
    > * pointer and dm_buffer pointer is no longer valid after this call.
    > */


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