[Qemu-devel] [PATCH] block/quorum: add simple read pattern support

[Qemu-devel] [PATCH] block/quorum: add simple read pattern support

[Liu Yuan]

This patch adds single read pattern to quorum driver and quorum vote is default
pattern.

For now we do a quorum vote on all the reads, it is designed for unreliable
underlying storage such as non-redundant NFS to make sure data integrity at the
cost of the read performance.

For some use cases as following:

        VM
  --------------
  |            |
  v            v
  A            B

Both A and B has hardware raid storage to justify the data integrity on its own.
So it would help performance if we do a single read instead of on all the nodes.
Further, if we run VM on either of the storage node, we can make a local read
request for better performance.

This patch generalize the above 2 nodes case in the N nodes. That is,

vm -> write to all the N nodes, read just one of them. If single read fails, we
try to read next node in FIFO order specified by the startup command.

The 2 nodes case is very similar to DRBD[1] though lack of auto-sync
functionality in the single device/node failure for now. But compared with DRBD
we still have some advantages over it:

- Suppose we have 20 VMs running on one(assume A) of 2 nodes' DRBD backed
storage. And if A crashes, we need to restart all the VMs on node B. But for
practice case, we can't because B might not have enough resources to setup 20 VMs
at once. So if we run our 20 VMs with quorum driver, and scatter the replicated
images over the data center, we can very likely restart 20 VMs without any
resource problem.

After all, I think we can build a more powerful replicated image functionality
on quorum and block jobs(block mirror) to meet various High Availibility needs.

E.g, Enable single read pattern on 2 children,

-drive driver=quorum,children.0.file.filename=0.qcow2,\
children.1.file.filename=1.qcow2,read-pattern=single,vote-threshold=1

[1] http://en.wikipedia.org/wiki/Distributed_Replicated_Block_Device

Cc: Benoit Canet <benoit@irqsave.net>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
---
 block/quorum.c | 174 +++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 125 insertions(+), 49 deletions(-)

diff --git a/block/quorum.c b/block/quorum.c
index d5ee9c0..2f18755 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -24,6 +24,7 @@
 #define QUORUM_OPT_VOTE_THRESHOLD "vote-threshold"
 #define QUORUM_OPT_BLKVERIFY      "blkverify"
 #define QUORUM_OPT_REWRITE        "rewrite-corrupted"
+#define QUORUM_OPT_READ_PATTERN   "read-pattern"
 
 /* This union holds a vote hash value */
 typedef union QuorumVoteValue {
@@ -74,6 +75,16 @@ typedef struct BDRVQuorumState {
     bool rewrite_corrupted;/* true if the driver must rewrite-on-read corrupted
                             * block if Quorum is reached.
                             */
+
+#define READ_PATTERN_QUORUM 0 /* default */
+#define READ_PATTERN_SINGLE 1
+    int read_pattern;      /* single: read a single child and try first one
+                            *         first. If error, try next child in an
+                            *         FIFO order specifed by command line.
+                            *         Return error if no child read succeeds.
+                            * quorum: read all the children and do a quorum
+                            *         vote on reads.
+                            */
 } BDRVQuorumState;
 
 typedef struct QuorumAIOCB QuorumAIOCB;
@@ -117,6 +128,7 @@ struct QuorumAIOCB {
 
     bool is_read;
     int vote_ret;
+    int child_iter;             /* which child to read in single pattern */
 };
 
 static bool quorum_vote(QuorumAIOCB *acb);
@@ -256,6 +268,21 @@ static void quorum_rewrite_aio_cb(void *opaque, int ret)
     quorum_aio_finalize(acb);
 }
 
+static BlockDriverAIOCB *read_single_child(QuorumAIOCB *acb);
+
+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_aio_cb(void *opaque, int ret)
 {
     QuorumChildRequest *sacb = opaque;
@@ -263,6 +290,21 @@ static void quorum_aio_cb(void *opaque, int ret)
     BDRVQuorumState *s = acb->common.bs->opaque;
     bool rewrite = false;
 
+    if (acb->is_read && s->read_pattern == READ_PATTERN_SINGLE) {
+        /* We try to read next child in FIFO order if we fail to read */
+        if (ret < 0 && ++acb->child_iter < s->num_children) {
+            read_single_child(acb);
+            return;
+        }
+
+        if (ret == 0) {
+            quorum_copy_qiov(acb->qiov, &acb->qcrs[acb->child_iter].qiov);
+        }
+        acb->vote_ret = ret;
+        quorum_aio_finalize(acb);
+        return;
+    }
+
     sacb->ret = ret;
     acb->count++;
     if (ret == 0) {
@@ -276,7 +318,6 @@ static void quorum_aio_cb(void *opaque, int ret)
         return;
     }
 
-    /* Do the vote on read */
     if (acb->is_read) {
         rewrite = quorum_vote(acb);
     } else {
@@ -343,19 +384,6 @@ static bool quorum_rewrite_bad_versions(BDRVQuorumState *s, QuorumAIOCB *acb,
     return count;
 }
 
-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)
@@ -615,34 +643,61 @@ free_exit:
     return rewrite;
 }
 
-static BlockDriverAIOCB *quorum_aio_readv(BlockDriverState *bs,
-                                         int64_t sector_num,
-                                         QEMUIOVector *qiov,
-                                         int nb_sectors,
-                                         BlockDriverCompletionFunc *cb,
-                                         void *opaque)
+static BlockDriverAIOCB *read_all_children(QuorumAIOCB *acb)
 {
-    BDRVQuorumState *s = bs->opaque;
-    QuorumAIOCB *acb = quorum_aio_get(s, bs, qiov, sector_num,
-                                      nb_sectors, cb, opaque);
+    BDRVQuorumState *s = acb->common.bs->opaque;
     int i;
 
-    acb->is_read = true;
-
     for (i = 0; i < s->num_children; i++) {
-        acb->qcrs[i].buf = qemu_blockalign(s->bs[i], qiov->size);
-        qemu_iovec_init(&acb->qcrs[i].qiov, qiov->niov);
-        qemu_iovec_clone(&acb->qcrs[i].qiov, qiov, acb->qcrs[i].buf);
+        acb->qcrs[i].buf = qemu_blockalign(s->bs[i], acb->qiov->size);
+        qemu_iovec_init(&acb->qcrs[i].qiov, acb->qiov->niov);
+        qemu_iovec_clone(&acb->qcrs[i].qiov, acb->qiov, acb->qcrs[i].buf);
     }
 
     for (i = 0; i < s->num_children; i++) {
-        bdrv_aio_readv(s->bs[i], sector_num, &acb->qcrs[i].qiov, nb_sectors,
-                       quorum_aio_cb, &acb->qcrs[i]);
+        bdrv_aio_readv(s->bs[i], acb->sector_num, &acb->qcrs[i].qiov,
+                       acb->nb_sectors, quorum_aio_cb, &acb->qcrs[i]);
     }
 
     return &acb->common;
 }
 
+static BlockDriverAIOCB *read_single_child(QuorumAIOCB *acb)
+{
+    BDRVQuorumState *s = acb->common.bs->opaque;
+
+    acb->qcrs[acb->child_iter].buf = qemu_blockalign(s->bs[acb->child_iter],
+                                                     acb->qiov->size);
+    qemu_iovec_init(&acb->qcrs[acb->child_iter].qiov, acb->qiov->niov);
+    qemu_iovec_clone(&acb->qcrs[acb->child_iter].qiov, acb->qiov,
+                     acb->qcrs[acb->child_iter].buf);
+    bdrv_aio_readv(s->bs[acb->child_iter], acb->sector_num,
+                   &acb->qcrs[acb->child_iter].qiov, acb->nb_sectors,
+                   quorum_aio_cb, &acb->qcrs[acb->child_iter]);
+
+    return &acb->common;
+}
+
+static BlockDriverAIOCB *quorum_aio_readv(BlockDriverState *bs,
+                                          int64_t sector_num,
+                                          QEMUIOVector *qiov,
+                                          int nb_sectors,
+                                          BlockDriverCompletionFunc *cb,
+                                          void *opaque)
+{
+    BDRVQuorumState *s = bs->opaque;
+    QuorumAIOCB *acb = quorum_aio_get(s, bs, qiov, sector_num,
+                                      nb_sectors, cb, opaque);
+    acb->is_read = true;
+
+    if (s->read_pattern == READ_PATTERN_QUORUM) {
+        return read_all_children(acb);
+    }
+
+    acb->child_iter = 0;
+    return read_single_child(acb);
+}
+
 static BlockDriverAIOCB *quorum_aio_writev(BlockDriverState *bs,
                                           int64_t sector_num,
                                           QEMUIOVector *qiov,
@@ -782,6 +837,11 @@ static QemuOptsList quorum_runtime_opts = {
             .type = QEMU_OPT_BOOL,
             .help = "Rewrite corrupted block on read quorum",
         },
+        {
+            .name = QUORUM_OPT_READ_PATTERN,
+            .type = QEMU_OPT_STRING,
+            .help = "Allowed pattern: quorum, single. Quorum is default",
+        },
         { /* end of list */ }
     },
 };
@@ -796,6 +856,7 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
     QDict *sub = NULL;
     QList *list = NULL;
     const QListEntry *lentry;
+    const char *read_pattern;
     int i;
     int ret = 0;
 
@@ -827,28 +888,43 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     s->threshold = qemu_opt_get_number(opts, QUORUM_OPT_VOTE_THRESHOLD, 0);
-
-    /* and validate it against s->num_children */
-    ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
-    if (ret < 0) {
-        goto exit;
+    read_pattern = qemu_opt_get(opts, QUORUM_OPT_READ_PATTERN);
+    if (read_pattern) {
+        if (strcmp(read_pattern, "single") == 0) {
+            s->read_pattern = READ_PATTERN_SINGLE;
+        } else if (strcmp(read_pattern, "quorum") == 0) {
+            s->read_pattern = READ_PATTERN_QUORUM;
+        } else {
+            error_setg(&local_err,
+                       "Please set read-pattern as single or quorum\n");
+            ret = -EINVAL;
+            goto exit;
+        }
     }
 
-    /* is the driver in blkverify mode */
-    if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false) &&
-        s->num_children == 2 && s->threshold == 2) {
-        s->is_blkverify = true;
-    } else if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false)) {
-        fprintf(stderr, "blkverify mode is set by setting blkverify=on "
-                "and using two files with vote_threshold=2\n");
-    }
+    if (s->read_pattern == READ_PATTERN_QUORUM) {
+        /* and validate it against s->num_children */
+        ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
+        if (ret < 0) {
+            goto exit;
+        }
 
-    s->rewrite_corrupted = qemu_opt_get_bool(opts, QUORUM_OPT_REWRITE, false);
-    if (s->rewrite_corrupted && s->is_blkverify) {
-        error_setg(&local_err,
-                   "rewrite-corrupted=on cannot be used with blkverify=on");
-        ret = -EINVAL;
-        goto exit;
+        /* is the driver in blkverify mode */
+        if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false) &&
+            s->num_children == 2 && s->threshold == 2) {
+            s->is_blkverify = true;
+        } else if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false)) {
+            fprintf(stderr, "blkverify mode is set by setting blkverify=on "
+                    "and using two files with vote_threshold=2\n");
+        }
+
+        s->rewrite_corrupted = qemu_opt_get_bool(opts, QUORUM_OPT_REWRITE, false);
+        if (s->rewrite_corrupted && s->is_blkverify) {
+            error_setg(&local_err,
+                       "rewrite-corrupted=on cannot be used with blkverify=on");
+            ret = -EINVAL;
+            goto exit;
+        }
     }
 
     /* allocate the children BlockDriverState array */
-- 
1.9.1

Re: [Qemu-devel] [PATCH] block/quorum: add simple read pattern support

[Benoît Canet]

The Friday 11 Jul 2014 à 11:01:22 (+0800), Liu Yuan wrote :
> This patch adds single read pattern to quorum driver and quorum vote is default
> pattern.
> 
> For now we do a quorum vote on all the reads, it is designed for unreliable
> underlying storage such as non-redundant NFS to make sure data integrity at the
> cost of the read performance.
> 
> For some use cases as following:
> 
>         VM
>   --------------
>   |            |
>   v            v
>   A            B
> 
> Both A and B has hardware raid storage to justify the data integrity on its own.
> So it would help performance if we do a single read instead of on all the nodes.
> Further, if we run VM on either of the storage node, we can make a local read
> request for better performance.
> 
> This patch generalize the above 2 nodes case in the N nodes. That is,
> 
> vm -> write to all the N nodes, read just one of them. If single read fails, we
> try to read next node in FIFO order specified by the startup command.
> 
> The 2 nodes case is very similar to DRBD[1] though lack of auto-sync
> functionality in the single device/node failure for now. But compared with DRBD
> we still have some advantages over it:
> 
> - Suppose we have 20 VMs running on one(assume A) of 2 nodes' DRBD backed
> storage. And if A crashes, we need to restart all the VMs on node B. But for
> practice case, we can't because B might not have enough resources to setup 20 VMs
> at once. So if we run our 20 VMs with quorum driver, and scatter the replicated
> images over the data center, we can very likely restart 20 VMs without any
> resource problem.
> 
> After all, I think we can build a more powerful replicated image functionality
> on quorum and block jobs(block mirror) to meet various High Availibility needs.
> 
> E.g, Enable single read pattern on 2 children,
> 
> -drive driver=quorum,children.0.file.filename=0.qcow2,\
> children.1.file.filename=1.qcow2,read-pattern=single,vote-threshold=1
> 
> [1] http://en.wikipedia.org/wiki/Distributed_Replicated_Block_Device
> 
> Cc: Benoit Canet <benoit@irqsave.net>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Liu Yuan <namei.unix@gmail.com>
> ---
>  block/quorum.c | 174 +++++++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 125 insertions(+), 49 deletions(-)
> 
> diff --git a/block/quorum.c b/block/quorum.c
> index d5ee9c0..2f18755 100644
> --- a/block/quorum.c
> +++ b/block/quorum.c
> @@ -24,6 +24,7 @@
>  #define QUORUM_OPT_VOTE_THRESHOLD "vote-threshold"
>  #define QUORUM_OPT_BLKVERIFY      "blkverify"
>  #define QUORUM_OPT_REWRITE        "rewrite-corrupted"
> +#define QUORUM_OPT_READ_PATTERN   "read-pattern"
>  
>  /* This union holds a vote hash value */
>  typedef union QuorumVoteValue {
> @@ -74,6 +75,16 @@ typedef struct BDRVQuorumState {
>      bool rewrite_corrupted;/* true if the driver must rewrite-on-read corrupted
>                              * block if Quorum is reached.
>                              */
> +
> +#define READ_PATTERN_QUORUM 0 /* default */
> +#define READ_PATTERN_SINGLE 1

Why not making these choices an enum ?

Would READ_PATTERN_SINGLE be more accuratelly described by READ_PATTERN_ROUND_ROBIN ?

More generaly would s/single/round-robin/ be more descriptive.

> +    int read_pattern;      /* single: read a single child and try first one
> +                            *         first. If error, try next child in an
> +                            *         FIFO order specifed by command line.
> +                            *         Return error if no child read succeeds.
> +                            * quorum: read all the children and do a quorum
> +                            *         vote on reads.
> +                            */
>  } BDRVQuorumState;
>  
>  typedef struct QuorumAIOCB QuorumAIOCB;
> @@ -117,6 +128,7 @@ struct QuorumAIOCB {
>  
>      bool is_read;
>      int vote_ret;
> +    int child_iter;             /* which child to read in single pattern */
>  };
>  
>  static bool quorum_vote(QuorumAIOCB *acb);
> @@ -256,6 +268,21 @@ static void quorum_rewrite_aio_cb(void *opaque, int ret)
>      quorum_aio_finalize(acb);
>  }
>  
> +static BlockDriverAIOCB *read_single_child(QuorumAIOCB *acb);
> +
> +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_aio_cb(void *opaque, int ret)
>  {
>      QuorumChildRequest *sacb = opaque;
> @@ -263,6 +290,21 @@ static void quorum_aio_cb(void *opaque, int ret)
>      BDRVQuorumState *s = acb->common.bs->opaque;
>      bool rewrite = false;
>  
> +    if (acb->is_read && s->read_pattern == READ_PATTERN_SINGLE) {
> +        /* We try to read next child in FIFO order if we fail to read */
> +        if (ret < 0 && ++acb->child_iter < s->num_children) {
> +            read_single_child(acb);

Here the previous failed read is never finalized/freed.

> +            return;
> +        }
> +
> +        if (ret == 0) {
> +            quorum_copy_qiov(acb->qiov, &acb->qcrs[acb->child_iter].qiov);
> +        }
> +        acb->vote_ret = ret;
> +        quorum_aio_finalize(acb);
> +        return;
> +    }
> +
>      sacb->ret = ret;
>      acb->count++;
>      if (ret == 0) {
> @@ -276,7 +318,6 @@ static void quorum_aio_cb(void *opaque, int ret)
>          return;
>      }
>  
> -    /* Do the vote on read */

Why removing this comment ?

>      if (acb->is_read) {
>          rewrite = quorum_vote(acb);
>      } else {
> @@ -343,19 +384,6 @@ static bool quorum_rewrite_bad_versions(BDRVQuorumState *s, QuorumAIOCB *acb,
>      return count;
>  }
>  
> -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)
> @@ -615,34 +643,61 @@ free_exit:
>      return rewrite;
>  }
>  
> -static BlockDriverAIOCB *quorum_aio_readv(BlockDriverState *bs,
> -                                         int64_t sector_num,
> -                                         QEMUIOVector *qiov,
> -                                         int nb_sectors,
> -                                         BlockDriverCompletionFunc *cb,
> -                                         void *opaque)
> +static BlockDriverAIOCB *read_all_children(QuorumAIOCB *acb)
>  {
> -    BDRVQuorumState *s = bs->opaque;
> -    QuorumAIOCB *acb = quorum_aio_get(s, bs, qiov, sector_num,
> -                                      nb_sectors, cb, opaque);
> +    BDRVQuorumState *s = acb->common.bs->opaque;
>      int i;
>  
> -    acb->is_read = true;
> -
>      for (i = 0; i < s->num_children; i++) {
> -        acb->qcrs[i].buf = qemu_blockalign(s->bs[i], qiov->size);
> -        qemu_iovec_init(&acb->qcrs[i].qiov, qiov->niov);
> -        qemu_iovec_clone(&acb->qcrs[i].qiov, qiov, acb->qcrs[i].buf);
> +        acb->qcrs[i].buf = qemu_blockalign(s->bs[i], acb->qiov->size);
> +        qemu_iovec_init(&acb->qcrs[i].qiov, acb->qiov->niov);
> +        qemu_iovec_clone(&acb->qcrs[i].qiov, acb->qiov, acb->qcrs[i].buf);
>      }
>  
>      for (i = 0; i < s->num_children; i++) {
> -        bdrv_aio_readv(s->bs[i], sector_num, &acb->qcrs[i].qiov, nb_sectors,
> -                       quorum_aio_cb, &acb->qcrs[i]);
> +        bdrv_aio_readv(s->bs[i], acb->sector_num, &acb->qcrs[i].qiov,
> +                       acb->nb_sectors, quorum_aio_cb, &acb->qcrs[i]);
>      }
>  
>      return &acb->common;
>  }
>  
> +static BlockDriverAIOCB *read_single_child(QuorumAIOCB *acb)
> +{
> +    BDRVQuorumState *s = acb->common.bs->opaque;
> +
> +    acb->qcrs[acb->child_iter].buf = qemu_blockalign(s->bs[acb->child_iter],
> +                                                     acb->qiov->size);
> +    qemu_iovec_init(&acb->qcrs[acb->child_iter].qiov, acb->qiov->niov);
> +    qemu_iovec_clone(&acb->qcrs[acb->child_iter].qiov, acb->qiov,
> +                     acb->qcrs[acb->child_iter].buf);
> +    bdrv_aio_readv(s->bs[acb->child_iter], acb->sector_num,
> +                   &acb->qcrs[acb->child_iter].qiov, acb->nb_sectors,
> +                   quorum_aio_cb, &acb->qcrs[acb->child_iter]);
> +
> +    return &acb->common;
> +}
> +
> +static BlockDriverAIOCB *quorum_aio_readv(BlockDriverState *bs,
> +                                          int64_t sector_num,
> +                                          QEMUIOVector *qiov,
> +                                          int nb_sectors,
> +                                          BlockDriverCompletionFunc *cb,
> +                                          void *opaque)
> +{
> +    BDRVQuorumState *s = bs->opaque;
> +    QuorumAIOCB *acb = quorum_aio_get(s, bs, qiov, sector_num,
> +                                      nb_sectors, cb, opaque);
> +    acb->is_read = true;
> +
> +    if (s->read_pattern == READ_PATTERN_QUORUM) {
> +        return read_all_children(acb);
> +    }
> +
> +    acb->child_iter = 0;
> +    return read_single_child(acb);
> +}
> +
>  static BlockDriverAIOCB *quorum_aio_writev(BlockDriverState *bs,
>                                            int64_t sector_num,
>                                            QEMUIOVector *qiov,
> @@ -782,6 +837,11 @@ static QemuOptsList quorum_runtime_opts = {
>              .type = QEMU_OPT_BOOL,
>              .help = "Rewrite corrupted block on read quorum",
>          },
> +        {
> +            .name = QUORUM_OPT_READ_PATTERN,
> +            .type = QEMU_OPT_STRING,
> +            .help = "Allowed pattern: quorum, single. Quorum is default",
> +        },
>          { /* end of list */ }
>      },
>  };
> @@ -796,6 +856,7 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
>      QDict *sub = NULL;
>      QList *list = NULL;
>      const QListEntry *lentry;
> +    const char *read_pattern;
>      int i;
>      int ret = 0;
>  
> @@ -827,28 +888,43 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
>      }
>  
>      s->threshold = qemu_opt_get_number(opts, QUORUM_OPT_VOTE_THRESHOLD, 0);
> -
> -    /* and validate it against s->num_children */
> -    ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
> -    if (ret < 0) {
> -        goto exit;
> +    read_pattern = qemu_opt_get(opts, QUORUM_OPT_READ_PATTERN);
> +    if (read_pattern) {
> +        if (strcmp(read_pattern, "single") == 0) {
> +            s->read_pattern = READ_PATTERN_SINGLE;
> +        } else if (strcmp(read_pattern, "quorum") == 0) {
> +            s->read_pattern = READ_PATTERN_QUORUM;
> +        } else {
> +            error_setg(&local_err,
> +                       "Please set read-pattern as single or quorum\n");
> +            ret = -EINVAL;
> +            goto exit;
> +        }
>      }
>  
> -    /* is the driver in blkverify mode */
> -    if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false) &&
> -        s->num_children == 2 && s->threshold == 2) {
> -        s->is_blkverify = true;
> -    } else if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false)) {
> -        fprintf(stderr, "blkverify mode is set by setting blkverify=on "
> -                "and using two files with vote_threshold=2\n");
> -    }
> +    if (s->read_pattern == READ_PATTERN_QUORUM) {
> +        /* and validate it against s->num_children */
> +        ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
> +        if (ret < 0) {
> +            goto exit;
> +        }
>  
> -    s->rewrite_corrupted = qemu_opt_get_bool(opts, QUORUM_OPT_REWRITE, false);
> -    if (s->rewrite_corrupted && s->is_blkverify) {
> -        error_setg(&local_err,
> -                   "rewrite-corrupted=on cannot be used with blkverify=on");
> -        ret = -EINVAL;
> -        goto exit;
> +        /* is the driver in blkverify mode */
> +        if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false) &&
> +            s->num_children == 2 && s->threshold == 2) {
> +            s->is_blkverify = true;
> +        } else if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false)) {
> +            fprintf(stderr, "blkverify mode is set by setting blkverify=on "
> +                    "and using two files with vote_threshold=2\n");
> +        }
> +
> +        s->rewrite_corrupted = qemu_opt_get_bool(opts, QUORUM_OPT_REWRITE, false);
> +        if (s->rewrite_corrupted && s->is_blkverify) {
> +            error_setg(&local_err,
> +                       "rewrite-corrupted=on cannot be used with blkverify=on");
> +            ret = -EINVAL;
> +            goto exit;
> +        }
>      }
>  
>      /* allocate the children BlockDriverState array */
> -- 
> 1.9.1
> 

Re: [Qemu-devel] [PATCH] block/quorum: add simple read pattern support

[Eric Blake]

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On 07/10/2014 09:01 PM, Liu Yuan wrote:
> This patch adds single read pattern to quorum driver and quorum vote is default
> pattern.
> 
> For now we do a quorum vote on all the reads, it is designed for unreliable
> underlying storage such as non-redundant NFS to make sure data integrity at the
> cost of the read performance.
> 

> E.g, Enable single read pattern on 2 children,
> 
> -drive driver=quorum,children.0.file.filename=0.qcow2,\
> children.1.file.filename=1.qcow2,read-pattern=single,vote-threshold=1
> 
> [1] http://en.wikipedia.org/wiki/Distributed_Replicated_Block_Device
> 
> Cc: Benoit Canet <benoit@irqsave.net>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Liu Yuan <namei.unix@gmail.com>
> ---
>  block/quorum.c | 174 +++++++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 125 insertions(+), 49 deletions(-)

That covers the command line, but what about the *.json changes to allow
QMP to select this mode when hot-plugging?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH] block/quorum: add simple read pattern support

[Liu Yuan]

On Fri, Jul 11, 2014 at 12:56:53PM +0200, Benoît Canet wrote:
> The Friday 11 Jul 2014 à 11:01:22 (+0800), Liu Yuan wrote :
> > This patch adds single read pattern to quorum driver and quorum vote is default
> > pattern.
> > 
> > For now we do a quorum vote on all the reads, it is designed for unreliable
> > underlying storage such as non-redundant NFS to make sure data integrity at the
> > cost of the read performance.
> > 
> > For some use cases as following:
> > 
> >         VM
> >   --------------
> >   |            |
> >   v            v
> >   A            B
> > 
> > Both A and B has hardware raid storage to justify the data integrity on its own.
> > So it would help performance if we do a single read instead of on all the nodes.
> > Further, if we run VM on either of the storage node, we can make a local read
> > request for better performance.
> > 
> > This patch generalize the above 2 nodes case in the N nodes. That is,
> > 
> > vm -> write to all the N nodes, read just one of them. If single read fails, we
> > try to read next node in FIFO order specified by the startup command.
> > 
> > The 2 nodes case is very similar to DRBD[1] though lack of auto-sync
> > functionality in the single device/node failure for now. But compared with DRBD
> > we still have some advantages over it:
> > 
> > - Suppose we have 20 VMs running on one(assume A) of 2 nodes' DRBD backed
> > storage. And if A crashes, we need to restart all the VMs on node B. But for
> > practice case, we can't because B might not have enough resources to setup 20 VMs
> > at once. So if we run our 20 VMs with quorum driver, and scatter the replicated
> > images over the data center, we can very likely restart 20 VMs without any
> > resource problem.
> > 
> > After all, I think we can build a more powerful replicated image functionality
> > on quorum and block jobs(block mirror) to meet various High Availibility needs.
> > 
> > E.g, Enable single read pattern on 2 children,
> > 
> > -drive driver=quorum,children.0.file.filename=0.qcow2,\
> > children.1.file.filename=1.qcow2,read-pattern=single,vote-threshold=1
> > 
> > [1] http://en.wikipedia.org/wiki/Distributed_Replicated_Block_Device
> > 
> > Cc: Benoit Canet <benoit@irqsave.net>
> > Cc: Kevin Wolf <kwolf@redhat.com>
> > Cc: Stefan Hajnoczi <stefanha@redhat.com>
> > Signed-off-by: Liu Yuan <namei.unix@gmail.com>
> > ---
> >  block/quorum.c | 174 +++++++++++++++++++++++++++++++++++++++++----------------
> >  1 file changed, 125 insertions(+), 49 deletions(-)
> > 
> > diff --git a/block/quorum.c b/block/quorum.c
> > index d5ee9c0..2f18755 100644
> > --- a/block/quorum.c
> > +++ b/block/quorum.c
> > @@ -24,6 +24,7 @@
> >  #define QUORUM_OPT_VOTE_THRESHOLD "vote-threshold"
> >  #define QUORUM_OPT_BLKVERIFY      "blkverify"
> >  #define QUORUM_OPT_REWRITE        "rewrite-corrupted"
> > +#define QUORUM_OPT_READ_PATTERN   "read-pattern"
> >  
> >  /* This union holds a vote hash value */
> >  typedef union QuorumVoteValue {
> > @@ -74,6 +75,16 @@ typedef struct BDRVQuorumState {
> >      bool rewrite_corrupted;/* true if the driver must rewrite-on-read corrupted
> >                              * block if Quorum is reached.
> >                              */
> > +
> > +#define READ_PATTERN_QUORUM 0 /* default */
> > +#define READ_PATTERN_SINGLE 1
> 
> Why not making these choices an enum ?

It is just a matter of taste. For now we only have 2 constants and the bonus to
have #define here is we can put them near the 'read_pattern' for easier code
read.

> Would READ_PATTERN_SINGLE be more accuratelly described by READ_PATTERN_ROUND_ROBIN ?

How about FIFO? Since 'quorum' is a single word...

> More generaly would s/single/round-robin/ be more descriptive.

ditto.

> 
> > +    int read_pattern;      /* single: read a single child and try first one
> > +                            *         first. If error, try next child in an
> > +                            *         FIFO order specifed by command line.
> > +                            *         Return error if no child read succeeds.
> > +                            * quorum: read all the children and do a quorum
> > +                            *         vote on reads.
> > +                            */
> >  } BDRVQuorumState;
> >  
> >  typedef struct QuorumAIOCB QuorumAIOCB;
> > @@ -117,6 +128,7 @@ struct QuorumAIOCB {
> >  
> >      bool is_read;
> >      int vote_ret;
> > +    int child_iter;             /* which child to read in single pattern */
> >  };
> >  
> >  static bool quorum_vote(QuorumAIOCB *acb);
> > @@ -256,6 +268,21 @@ static void quorum_rewrite_aio_cb(void *opaque, int ret)
> >      quorum_aio_finalize(acb);
> >  }
> >  
> > +static BlockDriverAIOCB *read_single_child(QuorumAIOCB *acb);
> > +
> > +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_aio_cb(void *opaque, int ret)
> >  {
> >      QuorumChildRequest *sacb = opaque;
> > @@ -263,6 +290,21 @@ static void quorum_aio_cb(void *opaque, int ret)
> >      BDRVQuorumState *s = acb->common.bs->opaque;
> >      bool rewrite = false;
> >  
> > +    if (acb->is_read && s->read_pattern == READ_PATTERN_SINGLE) {
> > +        /* We try to read next child in FIFO order if we fail to read */
> > +        if (ret < 0 && ++acb->child_iter < s->num_children) {
> > +            read_single_child(acb);
> 
> Here the previous failed read is never finalized/freed.

quorum_aio_finalize() will free all the reads. But yes, I need to modify
quorum_aio_finalize() to free exact reads we have done (all the failed read +
succeeded read)

> > +            return;
> > +        }
> > +
> > +        if (ret == 0) {
> > +            quorum_copy_qiov(acb->qiov, &acb->qcrs[acb->child_iter].qiov);
> > +        }
> > +        acb->vote_ret = ret;
> > +        quorum_aio_finalize(acb);
> > +        return;
> > +    }
> > +
> >      sacb->ret = ret;
> >      acb->count++;
> >      if (ret == 0) {
> > @@ -276,7 +318,6 @@ static void quorum_aio_cb(void *opaque, int ret)
> >          return;
> >      }
> >  
> > -    /* Do the vote on read */
> 
> Why removing this comment ?

Hmmm, probably at then time I thought the name of quorum_vote() already desribed
it. But yes, I shouldn't touch the lines that I don't modify.

Thanks
Yuan

Re: [Qemu-devel] [PATCH] block/quorum: add simple read pattern support

[Liu Yuan]

On Fri, Jul 11, 2014 at 08:06:36AM -0600, Eric Blake wrote:
> On 07/10/2014 09:01 PM, Liu Yuan wrote:
> > This patch adds single read pattern to quorum driver and quorum vote is default
> > pattern.
> > 
> > For now we do a quorum vote on all the reads, it is designed for unreliable
> > underlying storage such as non-redundant NFS to make sure data integrity at the
> > cost of the read performance.
> > 
> 
> > E.g, Enable single read pattern on 2 children,
> > 
> > -drive driver=quorum,children.0.file.filename=0.qcow2,\
> > children.1.file.filename=1.qcow2,read-pattern=single,vote-threshold=1
> > 
> > [1] http://en.wikipedia.org/wiki/Distributed_Replicated_Block_Device
> > 
> > Cc: Benoit Canet <benoit@irqsave.net>
> > Cc: Kevin Wolf <kwolf@redhat.com>
> > Cc: Stefan Hajnoczi <stefanha@redhat.com>
> > Signed-off-by: Liu Yuan <namei.unix@gmail.com>
> > ---
> >  block/quorum.c | 174 +++++++++++++++++++++++++++++++++++++++++----------------
> >  1 file changed, 125 insertions(+), 49 deletions(-)
> 
> That covers the command line, but what about the *.json changes to allow
> QMP to select this mode when hot-plugging?

Good catch, thanks for reminding.

Yuan