Re: [Qemu-devel] [PATCH V9 06/11] quorum: Add quorum mechanism.

[Benoît Canet]

Le Friday 04 Oct 2013 à 16:48:12 (+0200), Max Reitz a écrit :
> On 2013-10-02 14:39, Benoît Canet wrote:
> >Use gnutls's SHA-256 to compare versions.
> Wouldn't CRC32 suffice? (I don't really oppose using SHA, but taking
> in gnutls as a dependency just for comparing several memory areas
> seems a bit much to me)
> 
> >Signed-off-by: Benoit Canet <address@hidden>
> >---
> >  block/Makefile.objs       |   2 +-
> >  block/quorum.c            | 321 
> > +++++++++++++++++++++++++++++++++++++++++++++-
> >  configure                 |  36 ++++++
> >  include/monitor/monitor.h |   2 +
> >  monitor.c                 |   2 +
> >  5 files changed, 361 insertions(+), 2 deletions(-)
> >
> >diff --git a/block/Makefile.objs b/block/Makefile.objs
> >index 05a65c2..adcdc21 100644
> >--- a/block/Makefile.objs
> >+++ b/block/Makefile.objs
> >@@ -3,7 +3,7 @@ block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o 
> >qcow2-snapshot.o qcow2-c
> >  block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
> >  block-obj-y += qed-check.o
> >  block-obj-y += vhdx.o
> >-block-obj-y += quorum.o
> >+block-obj-$(CONFIG_QUORUM) += quorum.o
> >  block-obj-y += parallels.o blkdebug.o blkverify.o
> >  block-obj-y += snapshot.o qapi.o
> >  block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
> >diff --git a/block/quorum.c b/block/quorum.c
> >index f0fc0e9..e235ac1 100644
> >--- a/block/quorum.c
> >+++ b/block/quorum.c
> >@@ -13,7 +13,43 @@
> >   * See the COPYING file in the top-level directory.
> >   */
> >+#include <gnutls/gnutls.h>
> >+#include <gnutls/crypto.h>
> >  #include "block/block_int.h"
> >+#include "qapi/qmp/qjson.h"
> >+
> >+#define HASH_LENGTH 32
> >+
> >+/* This union hold a vote hash value */
> *holds
> 
> >+typedef union QuorumVoteValue {
> >+    char h[HASH_LENGTH];       /* SHA-256 hash */
> >+    int64_t l;                 /* simpler 64 bits hash */
> >+} QuorumVoteValue;
> >+
> >+/* A vote item */
> >+typedef struct QuorumVoteItem {
> >+    int index;
> >+    QLIST_ENTRY(QuorumVoteItem) next;
> >+} QuorumVoteItem;
> >+
> >+/* this structure is a vote version. A version is the set of vote sharing 
> >the
> *set of votes
> 
> >+ * same vote value.
> >+ * The set of vote will be tracked with the items field and it's count is
> *set of votes or *vote set; also s/it's count/its cardinality/ or
> something like that
> 
> >+ * vote_count.
> >+ */
> >+typedef struct QuorumVoteVersion {
> >+    QuorumVoteValue value;
> >+    int index;
> >+    int vote_count;
> >+    QLIST_HEAD(, QuorumVoteItem) items;
> >+    QLIST_ENTRY(QuorumVoteVersion) next;
> >+} QuorumVoteVersion;
> >+
> >+/* this structure hold a group of vote versions together */
> *holds
> 
> >+typedef struct QuorumVotes {
> >+    QLIST_HEAD(, QuorumVoteVersion) vote_list;
> >+    int (*compare)(QuorumVoteValue *a, QuorumVoteValue *b);
> >+} QuorumVotes;
> >  /* the following structure hold the state of one quorum instance */
> >  typedef struct {
> >@@ -60,10 +96,14 @@ struct QuorumAIOCB {
> >      int success_count;          /* number of successfully completed AIOCB 
> > */
> >      bool *finished;             /* completion signal for cancel */
> >+    QuorumVotes votes;
> >+
> >      bool is_read;
> >      int vote_ret;
> >  };
> >+static void quorum_vote(QuorumAIOCB *acb);
> >+
> >  static void quorum_aio_cancel(BlockDriverAIOCB *blockacb)
> >  {
> >      QuorumAIOCB *acb = container_of(blockacb, QuorumAIOCB, common);
> >@@ -111,6 +151,10 @@ static void quorum_aio_finalize(QuorumAIOCB *acb)
> >          acb->aios[i].ret = 0;
> >      }
> >+    if (acb->vote_ret) {
> >+        ret = acb->vote_ret;
> >+    }
> >+
> >      acb->common.cb(acb->common.opaque, ret);
> >      if (acb->finished) {
> >          *acb->finished = true;
> >@@ -122,6 +166,11 @@ static void quorum_aio_finalize(QuorumAIOCB *acb)
> >      qemu_aio_release(acb);
> >  }
> >+static int quorum_sha256_compare(QuorumVoteValue *a, QuorumVoteValue *b)
> >+{
> >+    return memcmp(a->h, b->h, HASH_LENGTH);
> >+}
> >+
> >  static QuorumAIOCB *quorum_aio_get(BDRVQuorumState *s,
> >                                     BlockDriverState *bs,
> >                                     QEMUIOVector *qiov,
> >@@ -141,6 +190,7 @@ static QuorumAIOCB *quorum_aio_get(BDRVQuorumState *s,
> >      acb->count = 0;
> >      acb->success_count = 0;
> >      acb->finished = NULL;
> >+    acb->votes.compare = quorum_sha256_compare;
> >      acb->is_read = false;
> >      acb->vote_ret = 0;
> >@@ -170,9 +220,278 @@ static void quorum_aio_cb(void *opaque, int ret)
> >          return;
> >      }
> >+    /* Do the vote on read */
> >+    if (acb->is_read) {
> >+        quorum_vote(acb);
> >+    }
> >+
> >      quorum_aio_finalize(acb);
> >  }
> >+static void quorum_report_bad(QuorumAIOCB *acb, int index)
> >+{
> >+    QObject *data;
> >+    data = qobject_from_jsonf("{ 'children-index': %i"
> I'd prefer child-index. Generally, remember that the singular of
> "children" is "child".
> 
> >+                              ", 'sector-num': %" PRId64
> >+                              ", 'sectors-count': %i }",
> >+                              index,
> >+                              acb->sector_num,
> >+                              acb->nb_sectors);
> >+    monitor_protocol_event(QEVENT_QUORUM_REPORT_BAD, data);
> How about decrementing the refcount of data?
> 
> >+}
> >+
> >+static void quorum_report_failure(QuorumAIOCB *acb)
> >+{
> >+    QObject *data;
> >+    data = qobject_from_jsonf("{ 'sector-num': %" PRId64
> >+                              ", 'sectors-count': %i }",
> >+                              acb->sector_num,
> >+                              acb->nb_sectors);
> >+    monitor_protocol_event(QEVENT_QUORUM_FAILURE, data);
> Same here.
> 
> >+}
> >+
> >+static void quorum_report_bad_versions(QuorumAIOCB *acb,
> >+                                      QuorumVoteValue *value)
> >+{
> >+    QuorumVoteVersion *version;
> >+    QuorumVoteItem *item;
> >+
> >+    QLIST_FOREACH(version, &acb->votes.vote_list, next) {
> >+        if (!acb->votes.compare(&version->value, value)) {
> >+            continue;
> >+        }
> >+        QLIST_FOREACH(item, &version->items, next) {
> >+            quorum_report_bad(acb, item->index);
> >+        }
> >+    }
> >+}
> >+
> >+static void quorum_copy_qiov(QEMUIOVector *dest, QEMUIOVector *source)
> >+{
> >+    int i;
> >+    assert(dest->niov == source->niov);
> >+    assert(dest->size == source->size);
> >+    for (i = 0; i < source->niov; i++) {
> >+        assert(dest->iov[i].iov_len == source->iov[i].iov_len);
> >+        memcpy(dest->iov[i].iov_base,
> >+               source->iov[i].iov_base,
> >+               source->iov[i].iov_len);
> >+    }
> >+}
> >+
> >+static void quorum_count_vote(QuorumVotes *votes,
> >+                              QuorumVoteValue *value,
> >+                              int index)
> >+{
> >+    QuorumVoteVersion *v = NULL, *version = NULL;
> >+    QuorumVoteItem *item;
> >+
> >+    /* look if we have something with this hash */
> >+    QLIST_FOREACH(v, &votes->vote_list, next) {
> >+        if (!votes->compare(&v->value, value)) {
> >+            version = v;
> >+            break;
> >+        }
> >+    }
> >+
> >+    /* It's a version not yet in the list add it */
> >+    if (!version) {
> >+        version = g_new0(QuorumVoteVersion, 1);
> >+        QLIST_INIT(&version->items);
> >+        memcpy(&version->value, value, sizeof(version->value));
> >+        version->index = index;
> >+        version->vote_count = 0;
> >+        QLIST_INSERT_HEAD(&votes->vote_list, version, next);
> >+    }
> >+
> >+    version->vote_count++;
> >+
> >+    item = g_new0(QuorumVoteItem, 1);
> >+    item->index = index;
> >+    QLIST_INSERT_HEAD(&version->items, item, next);
> >+}
> >+
> >+static void quorum_free_vote_list(QuorumVotes *votes)
> >+{
> >+    QuorumVoteVersion *version, *next_version;
> >+    QuorumVoteItem *item, *next_item;
> >+
> >+    QLIST_FOREACH_SAFE(version, &votes->vote_list, next, next_version) {
> >+        QLIST_REMOVE(version, next);
> >+        QLIST_FOREACH_SAFE(item, &version->items, next, next_item) {
> >+            QLIST_REMOVE(item, next);
> >+            g_free(item);
> >+        }
> >+        g_free(version);
> >+    }
> >+}
> >+
> >+static int quorum_compute_hash(QuorumAIOCB *acb, int i, QuorumVoteValue 
> >*hash)
> >+{
> >+    int j, ret;
> >+    gnutls_hash_hd_t dig;
> >+    QEMUIOVector *qiov = &acb->aios[i].qiov;
> >+
> >+    ret = gnutls_hash_init(&dig, GNUTLS_DIG_SHA256);
> >+
> >+    if (ret < 0) {
> >+        return ret;
> >+    }
> >+
> >+    for (j = 0; j < qiov->niov; j++) {
> >+        ret = gnutls_hash(dig, qiov->iov[j].iov_base, qiov->iov[j].iov_len);
> >+        if (ret < 0) {
> >+            return ret;
> gnutls_hash_deinit?
> 
> >+        }
> >+    }
> >+
> >+    gnutls_hash_deinit(dig, (void *) hash);
> >+
> >+    return 0;
> >+}
> >+
> >+static QuorumVoteVersion *quorum_get_vote_winner(QuorumVotes *votes)
> >+{
> >+    int i = 0;
> >+    QuorumVoteVersion *candidate, *winner = NULL;
> >+
> >+    QLIST_FOREACH(candidate, &votes->vote_list, next) {
> >+        if (candidate->vote_count > i) {
> >+            i = candidate->vote_count;
> >+            winner = candidate;
> >+        }
> >+    }
> >+
> >+    return winner;
> >+}
> >+
> >+static bool quorum_iovec_compare(QEMUIOVector *a, QEMUIOVector *b)
> >+{
> >+    int i;
> >+    int result;
> >+
> >+    assert(a->niov == b->niov);
> >+    for (i = 0; i < a->niov; i++) {
> >+        assert(a->iov[i].iov_len == b->iov[i].iov_len);
> >+        result = memcmp(a->iov[i].iov_base,
> >+                        b->iov[i].iov_base,
> >+                        a->iov[i].iov_len);
> >+        if (result) {
> >+            return false;
> >+        }
> >+    }
> >+
> >+    return true;
> >+}
> >+
> >+static void GCC_FMT_ATTR(2, 3) quorum_err(QuorumAIOCB *acb,
> >+                                          const char *fmt, ...)
> >+{
> >+    va_list ap;
> >+
> >+    va_start(ap, fmt);
> >+    fprintf(stderr, "quorum: sector_num=%" PRId64 " nb_sectors=%d ",
> >+            acb->sector_num, acb->nb_sectors);
> >+    vfprintf(stderr, fmt, ap);
> >+    fprintf(stderr, "\n");
> >+    va_end(ap);
> >+    exit(1);
> >+}
> >+
> >+static bool quorum_compare(QuorumAIOCB *acb,
> >+                           QEMUIOVector *a,
> >+                           QEMUIOVector *b)
> >+{
> >+    BDRVQuorumState *s = acb->bqs;
> >+    ssize_t offset;
> >+
> >+    /* This driver will replace blkverify in this particular case */
> >+    if (s->is_blkverify) {
> >+        offset = qemu_iovec_compare(a, b);
> >+        if (offset != -1) {
> >+            quorum_err(acb, "contents mismatch in sector %" PRId64,
> >+                       acb->sector_num +
> >+                       (uint64_t)(offset / BDRV_SECTOR_SIZE));
> >+        }
> >+        return true;
> >+    }
> >+
> >+    return quorum_iovec_compare(a, b);
> >+}
> >+
> >+static void quorum_vote(QuorumAIOCB *acb)
> >+{
> >+    bool quorum = true;
> >+    int i, j, ret;
> >+    QuorumVoteValue hash;
> >+    BDRVQuorumState *s = acb->bqs;
> >+    QuorumVoteVersion *winner;
> >+
> >+    /* get the index of the first successful read */
> >+    for (i = 0; i < s->total; i++) {
> >+        if (!acb->aios[i].ret) {
> >+            break;
> >+        }
> >+    }
> >+
> >+    /* compare this read with all other successful read looking for quorum 
> >*/
> >+    for (j = i + 1; j < s->total; j++) {
> >+        if (acb->aios[j].ret) {
> >+            continue;
> >+        }
> >+        quorum = quorum_compare(acb, &acb->aios[i].qiov, 
> >&acb->aios[j].qiov);
> >+        if (!quorum) {
> >+            break;
> >+       }
> >+    }
> >+
> >+    /* Every successful read agrees -> Quorum */
> >+    if (quorum) {
> >+        quorum_copy_qiov(acb->qiov, &acb->aios[i].qiov);
> If no reads were successful at all, quorum will be true and i will
> be s->total. Therefore, this will result in an array access with an
> index out of bounds here.
Thanks a lot for spotting this.

> 
> Generally, why is this function executed at all if any read failed?
> If a read fails, the quorum read function will return an error, thus
> the caller will ignore the result anyway.

I should if there is a quorum between the successfull reads; if all the success
ful reads agrees and their count is greater than threshold.

> 
> >+        return;
> >+    }
> >+
> >+    /* compute hashs for each successful read, also store indexes */
> >+    for (i = 0; i < s->total; i++) {
> >+        if (acb->aios[i].ret) {
> >+            continue;
> >+        }
> >+        ret = quorum_compute_hash(acb, i, &hash);
> >+        /* if ever the hash computation failed */
> >+        if (ret < 0) {
> >+            acb->vote_ret = ret;
> >+            goto free_exit;
> >+        }
> >+        quorum_count_vote(&acb->votes, &hash, i);
> >+    }
> >+
> >+    /* vote to select the most represented version */
> >+    winner = quorum_get_vote_winner(&acb->votes);
> >+    /* every vote version are differents -> error */
> >+    if (!winner) {
> >+        quorum_report_failure(acb);
> >+        acb->vote_ret = -EIO;
> >+        goto free_exit;
> >+    }
> >+
> >+    /* if the winner count is smaller then threshold read fail */
> s/then/than/, s/ read fail/, the read fails/
> 
> >+    if (winner->vote_count < s->threshold) {
> >+        quorum_report_failure(acb);
> >+        acb->vote_ret = -EIO;
> >+        goto free_exit;
> >+    }
> >+
> >+    /* we have a winner: copy it */
> >+    quorum_copy_qiov(acb->qiov, &acb->aios[winner->index].qiov);
> >+
> >+    /* some versions are bad print them */
> >+    quorum_report_bad_versions(acb, &winner->value);
> >+
> >+free_exit:
> >+    /* free lists */
> >+    quorum_free_vote_list(&acb->votes);
> >+}
> >+
> >  static BlockDriverAIOCB *quorum_aio_readv(BlockDriverState *bs,
> >                                           int64_t sector_num,
> >                                           QEMUIOVector *qiov,
> >@@ -194,7 +513,7 @@ static BlockDriverAIOCB 
> >*quorum_aio_readv(BlockDriverState *bs,
> >      }
> >      for (i = 0; i < s->total; i++) {
> >-        bdrv_aio_readv(&s->bs[i], sector_num, qiov, nb_sectors,
> >+        bdrv_aio_readv(&s->bs[i], sector_num, &acb->aios[i].qiov, 
> >nb_sectors,
> >                         quorum_aio_cb, &acb->aios[i]);
> >      }
> >diff --git a/configure b/configure
> >index 23dbaaf..efbe7d9 100755
> >--- a/configure
> >+++ b/configure
> >@@ -246,6 +246,7 @@ gtk=""
> >  gtkabi="2.0"
> >  tpm="no"
> >  libssh2=""
> >+quorum="no"
> >  # parse CC options first
> >  for opt do
> >@@ -972,6 +973,10 @@ for opt do
> >    ;;
> >    --enable-libssh2) libssh2="yes"
> >    ;;
> >+  --disable-quorum) quorum="no"
> >+  ;;
> >+  --enable-quorum) quorum="yes"
> >+  ;;
> >    *) echo "ERROR: unknown option $opt"; show_help="yes"
> >    ;;
> >    esac
> >@@ -1203,6 +1208,8 @@ echo "  --gcov=GCOV              use specified gcov 
> >[$gcov_tool]"
> >  echo "  --enable-tpm             enable TPM support"
> >  echo "  --disable-libssh2        disable ssh block device support"
> >  echo "  --enable-libssh2         enable ssh block device support"
> >+echo "  --disable-quorum         disable quorum block filter support"
> >+echo "  --enable-quorum          enable quorum block filter support"
> >  echo ""
> >  echo "NOTE: The object files are built at the place where configure is 
> > launched"
> >  exit 1
> >@@ -1895,6 +1902,30 @@ EOF
> >  fi
> >  ##########################################
> >+# Quorum probe (check for gnutls)
> >+if test "$quorum" != "no" ; then
> >+cat > $TMPC <<EOF
> >+#include <gnutls/gnutls.h>
> >+#include <gnutls/crypto.h>
> >+int main(void) {char data[4096], digest[32];
> >+gnutls_hash_fast(GNUTLS_DIG_SHA256, data, 4096, digest);
> >+return 0;
> >+}
> >+EOF
> >+quorum_tls_cflags=`$pkg_config --cflags gnutls 2> /dev/null`
> >+quorum_tls_libs=`$pkg_config --libs gnutls 2> /dev/null`
> >+if compile_prog "$quorum_tls_cflags" "$quorum_tls_libs" ; then
> >+  qcow_tls=yes
> >+  libs_softmmu="$quorum_tls_libs $libs_softmmu"
> >+  libs_tools="$quorum_tls_libs $libs_softmmu"
> >+  QEMU_CFLAGS="$QEMU_CFLAGS $quorum_tls_cflags"
> >+else
> >+  echo "gnutls > 2.10.0 required to compile Quorum"
> >+  exit 1
> >+fi
> >+fi
> >+
> >+##########################################
> >  # VNC SASL detection
> >  if test "$vnc" = "yes" -a "$vnc_sasl" != "no" ; then
> >    cat > $TMPC <<EOF
> >@@ -3758,6 +3789,7 @@ echo "TPM support       $tpm"
> >  echo "libssh2 support   $libssh2"
> >  echo "TPM passthrough   $tpm_passthrough"
> >  echo "QOM debugging     $qom_cast_debug"
> >+echo "Quorum            $quorum"
> >  if test "$sdl_too_old" = "yes"; then
> >  echo "-> Your SDL version is too old - please upgrade to have SDL support"
> >@@ -4156,6 +4188,10 @@ if test "$libssh2" = "yes" ; then
> >    echo "CONFIG_LIBSSH2=y" >> $config_host_mak
> >  fi
> >+if test "$quorum" = "yes" ; then
> >+  echo "CONFIG_QUORUM=y" >> $config_host_mak
> >+fi
> >+
> >  if test "$virtio_blk_data_plane" = "yes" ; then
> >    echo 'CONFIG_VIRTIO_BLK_DATA_PLANE=$(CONFIG_VIRTIO)' >> $config_host_mak
> >  fi
> >diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
> >index 10fa0e3..51902ed 100644
> >--- a/include/monitor/monitor.h
> >+++ b/include/monitor/monitor.h
> >@@ -49,6 +49,8 @@ typedef enum MonitorEvent {
> >      QEVENT_SPICE_MIGRATE_COMPLETED,
> >      QEVENT_GUEST_PANICKED,
> >      QEVENT_BLOCK_IMAGE_CORRUPTED,
> >+    QEVENT_QUORUM_FAILURE,
> >+    QEVENT_QUORUM_REPORT_BAD,
> >      /* Add to 'monitor_event_names' array in monitor.c when
> >       * defining new events here */
> >diff --git a/monitor.c b/monitor.c
> >index 74f3f1b..89d139f 100644
> >--- a/monitor.c
> >+++ b/monitor.c
> >@@ -507,6 +507,8 @@ static const char *monitor_event_names[] = {
> >      [QEVENT_SPICE_MIGRATE_COMPLETED] = "SPICE_MIGRATE_COMPLETED",
> >      [QEVENT_GUEST_PANICKED] = "GUEST_PANICKED",
> >      [QEVENT_BLOCK_IMAGE_CORRUPTED] = "BLOCK_IMAGE_CORRUPTED",
> >+    [QEVENT_QUORUM_FAILURE] = "QUORUM_FAILURE",
> >+    [QEVENT_QUORUM_REPORT_BAD] = "QUORUM_REPORT_BAD",
> Could you document these events in docs/qmp/qmp-events.txt?
> 
> Max
> 
> >  };
> >  QEMU_BUILD_BUG_ON(ARRAY_SIZE(monitor_event_names) != QEVENT_MAX)
> 
>