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 <ben...@irqsave.net>
> Cc: Kevin Wolf <kw...@redhat.com>
> Cc: Stefan Hajnoczi <stefa...@redhat.com>
> Signed-off-by: Liu Yuan <namei.u...@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
>
