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Re: [Qemu-devel] [PATCH v3 10/15] block: add block job transactions
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v3 10/15] block: add block job transactions |
Date: |
Tue, 14 Jul 2015 11:04:39 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Mon, 07/13 19:12, John Snow wrote:
>
>
> On 07/09/2015 11:46 PM, Fam Zheng wrote:
> > From: Stefan Hajnoczi <address@hidden>
> >
> > Sometimes block jobs must execute as a transaction group. Finishing
> > jobs wait until all other jobs are ready to complete successfully.
> > Failure or cancellation of one job cancels the other jobs in the group.
> >
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > [Rewrite the implementation which is now contained in block_job_completed.
> > --Fam]
> > Signed-off-by: Fam Zheng <address@hidden>
> > ---
> > blockjob.c | 86
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> > include/block/block.h | 1 +
> > include/block/blockjob.h | 26 +++++++++++++++
> > 3 files changed, 113 insertions(+)
> >
> > diff --git a/blockjob.c b/blockjob.c
> > index e057dd5..7b59b53 100644
> > --- a/blockjob.c
> > +++ b/blockjob.c
> > @@ -36,6 +36,16 @@
> > #include "qemu/timer.h"
> > #include "qapi-event.h"
> >
> > +/* Transactional group of block jobs */
> > +struct BlockJobTxn {
> > +
> > + /* Is this txn being cancelled? */
> > + bool aborting;
> > +
> > + /* List of jobs */
> > + QLIST_HEAD(, BlockJob) jobs;
> > +};
> > +
> > void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
> > int64_t speed, BlockCompletionFunc *cb,
> > void *opaque, Error **errp)
> > @@ -84,6 +94,59 @@ void block_job_release(BlockDriverState *bs)
> > g_free(job);
> > }
> >
> > +static void block_job_completed_txn(BlockJobTxn *txn, BlockJob *job, int
> > ret)
> > +{
> > + AioContext *ctx;
> > + BlockJob *other_job, *next;
> > + if (ret < 0 || block_job_is_cancelled(job)) {
> > + if (!txn->aborting) {
> > + /* We are the first failed job. Cancel other jobs. */
>
> What guarantee against a race is there at this point? Something to do
> with deferring back to the main loop before we call completion?
This is always in the main thread, so there can't be any race.
>
> Do jobs always complete in the main thread?
Yes.
>
> > + txn->aborting = true;
> > + QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
> > + if (other_job == job || other_job->completed) {
> > + continue;
> > + }
> > + ctx = bdrv_get_aio_context(other_job->bs);
> > + aio_context_acquire(ctx);
> > + block_job_cancel_sync(other_job);
> > + assert(other_job->completed);
> > + aio_context_release(ctx);
> > + }
> > + QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
> > + if (other_job->driver->txn_abort) {
> > + other_job->driver->txn_abort(other_job);
> > + }
> > + other_job->cb(other_job->opaque,
> > + other_job->ret ? : -ECANCELED);
> > + block_job_release(other_job->bs);
> > + }
> > + } else {
> > + /*
> > + * We are cancelled by another job, who will handle everything.
> > + */
> > + return;
> > + }
> > + } else {
> > + /*
> > + * Successful completion, see if there is other running jobs in
> > this
> > + * txn. */
>
> s/is/are/
OK.
>
> > + QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
> > + if (!other_job->completed) {
> > + return;
> > + }
> > + }
>
> Clever (though quadratic!) :~)
If someone suggest there could be 1000+ jobs in a txn, I can add a counter.
>
> > + /* We are the last completed job, commit the transaction. */
> > + QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
> > + if (other_job->driver->txn_commit) {
> > + other_job->driver->txn_commit(other_job);
> > + }
> > + assert(other_job->ret == 0);
> > + other_job->cb(other_job->opaque, 0);
> > + block_job_release(other_job->bs);
>
> Worth creating some static local/inline routine and sharing it with
> block_job_completed?
Mayb when a 3rd common line comes?
>
> > + }
> > + }
> > +}
> > +
> > void block_job_completed(BlockJob *job, int ret)
> > {
> > BlockDriverState *bs = job->bs;
> > @@ -96,6 +159,10 @@ void block_job_completed(BlockJob *job, int ret)
> > qemu_bh_delete(job->defer_to_main_loop_data.bh);
> > job->defer_to_main_loop_data.bh = NULL;
> > }
> > + if (job->txn) {
> > + block_job_completed_txn(job->txn, job, ret);
> > + return;
> > + }
> > job->cb(job->opaque, ret);
> > block_job_release(bs);
> > }
> > @@ -384,3 +451,22 @@ void block_job_defer_to_main_loop(BlockJob *job,
> >
> > qemu_bh_schedule(data->bh);
> > }
> > +
> > +BlockJobTxn *block_job_txn_new(void)
> > +{
> > + BlockJobTxn *txn = g_new0(BlockJobTxn, 1);
> > + QLIST_INIT(&txn->jobs);
> > + return txn;
> > +}
> > +
> > +void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job)
> > +{
> > + if (!txn) {
> > + return;
> > + }
> > +
> > + assert(!job->txn);
> > + job->txn = txn;
> > +
> > + QLIST_INSERT_HEAD(&txn->jobs, job, txn_list);
> > +}
> > diff --git a/include/block/block.h b/include/block/block.h
> > index 7437590..c7fc5b6 100644
> > --- a/include/block/block.h
> > +++ b/include/block/block.h
> > @@ -13,6 +13,7 @@
> > typedef struct BlockDriver BlockDriver;
> > typedef struct BlockJob BlockJob;
> > typedef struct BdrvChildRole BdrvChildRole;
> > +typedef struct BlockJobTxn BlockJobTxn;
> >
> > typedef struct BlockDriverInfo {
> > /* in bytes, 0 if irrelevant */
> > diff --git a/include/block/blockjob.h b/include/block/blockjob.h
> > index 5bac2e2..d854ee0 100644
> > --- a/include/block/blockjob.h
> > +++ b/include/block/blockjob.h
> > @@ -157,6 +157,9 @@ struct BlockJob {
> > */
> > int ret;
> >
> > + /** Non-NULL if this job is part of a transaction */
> > + BlockJobTxn *txn;
> > + QLIST_ENTRY(BlockJob) txn_list;
> > };
> >
> > /**
> > @@ -389,4 +392,27 @@ void block_job_defer_to_main_loop(BlockJob *job,
> > BlockJobDeferToMainLoopFn *fn,
> > void *opaque);
> >
> > +/**
> > + * block_job_txn_new:
> > + *
> > + * Allocate and return a new block job transaction. Jobs can be added to
> > the
> > + * transaction using block_job_txn_add_job().
> > + *
> > + * All jobs in the transaction either complete successfully or fail/cancel
> > as a
> > + * group. Jobs wait for each other before completing. Cancelling one job
> > + * cancels all jobs in the transaction.
> > + */
> > +BlockJobTxn *block_job_txn_new(void);
> > +
> > +/**
> > + * block_job_txn_add_job:
> > + * @txn: The transaction (may be NULL)
> > + * @job: Job to add to the transaction
> > + *
> > + * Add @job to the transaction. The @job must not already be in a
> > transaction.
> > + * The block job driver must call block_job_txn_prepare_to_complete()
> > before
> > + * final cleanup and completion.
> > + */
> > +void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job);
> > +
> > #endif
> >
>
> This definitely combines the best of our approaches AND has less code to
> boot. Great!
>
> Nitpicks and comment spelling aside:
> Reviewed-by: John Snow <address@hidden>
Thanks!
>
> --
> (linguistic postscript: I don't know how to say "Stefan and I's patches"
> because I think 'I' is incorrect here because the subject of the
> sentence is the patches, not Stefan or myself. I think it's some variant
> on "me" "my" or "mine," but can't quite work it out. English is hard, or
> I'm stupid, or both.)
>
LOL!
Fam
- Re: [Qemu-devel] [PATCH v3 06/15] blockjob: Add .txn_commit and .txn_abort transaction actions, (continued)
- [Qemu-devel] [PATCH v3 07/15] blockjob: Add "completed" and "ret" in BlockJob, Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 08/15] blockjob: Simplify block_job_finish_sync, Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 09/15] blockjob: Move BlockJobDeferToMainLoopData into BlockJob, Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 10/15] block: add block job transactions, Fam Zheng, 2015/07/09
- Re: [Qemu-devel] [PATCH v3 10/15] block: add block job transactions, Stefan Hajnoczi, 2015/07/14
- [Qemu-devel] [PATCH v3 11/15] blockdev: make BlockJobTxn available to qmp 'transaction', Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 12/15] block/backup: support block job transactions, Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 13/15] iotests: 124 - transactional failure test, Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 14/15] qmp-commands.hx: Update the supported 'transaction' operations, Fam Zheng, 2015/07/09
- [Qemu-devel] [PATCH v3 15/15] tests: add BlockJobTxn unit test, Fam Zheng, 2015/07/09