[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v3 10/15] block: add block job transactions
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [PATCH v3 10/15] block: add block job transactions |
Date: |
Tue, 14 Jul 2015 11:05:23 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
On 07/13/2015 11:04 PM, Fam Zheng wrote:
> 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.
>
Thought as much, now I know, thanks.
>>
>>> + 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.
>
My idea of a joke. Forgive me :)
>>
>>> + /* 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?
Fine by me, just my habit of asking out loud. The answer can always
simply be "I don't feel like it."
>>
>>> + }
>>> + }
>>> +}
>>> +
>>> 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
>
- [Qemu-devel] [PATCH v3 07/15] blockjob: Add "completed" and "ret" in BlockJob, (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