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Re: [Qemu-devel] [PATCH v5 04/16] block/commit: refactor commit to use j
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] [PATCH v5 04/16] block/commit: refactor commit to use job callbacks |
Date: |
Thu, 6 Sep 2018 12:19:52 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Thu, Sep 06, 2018 at 09:02:13AM -0400, John Snow wrote:
> Use the component callbacks; prepare, abort, and clean.
>
> NB: prepare is only called when the job has not yet failed;
> and abort can be called after prepare.
>
> complete -> prepare -> abort -> clean
> complete -> abort -> clean
>
> During refactor, a potential problem with bdrv_drop_intermediate
> was identified, The patched behavior is no worse than the pre-patch
> behavior, so leave a FIXME for now to be fixed in a future patch.
>
> Signed-off-by: John Snow <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>
Reviewed-by: Jeff Cody <address@hidden>
> ---
> block/commit.c | 92
> ++++++++++++++++++++++++++++++++--------------------------
> 1 file changed, 51 insertions(+), 41 deletions(-)
>
> diff --git a/block/commit.c b/block/commit.c
> index b6e8969877..a2da5740b0 100644
> --- a/block/commit.c
> +++ b/block/commit.c
> @@ -36,6 +36,7 @@ typedef struct CommitBlockJob {
> BlockDriverState *commit_top_bs;
> BlockBackend *top;
> BlockBackend *base;
> + BlockDriverState *base_bs;
> BlockdevOnError on_error;
> int base_flags;
> char *backing_file_str;
> @@ -68,61 +69,67 @@ static int coroutine_fn commit_populate(BlockBackend *bs,
> BlockBackend *base,
> return 0;
> }
>
> -static void commit_exit(Job *job)
> +static int commit_prepare(Job *job)
> {
> CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
> - BlockJob *bjob = &s->common;
> - BlockDriverState *top = blk_bs(s->top);
> - BlockDriverState *base = blk_bs(s->base);
> - BlockDriverState *commit_top_bs = s->commit_top_bs;
> - bool remove_commit_top_bs = false;
> -
> - /* Make sure commit_top_bs and top stay around until bdrv_replace_node()
> */
> - bdrv_ref(top);
> - bdrv_ref(commit_top_bs);
>
> /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
> * the normal backing chain can be restored. */
> blk_unref(s->base);
> + s->base = NULL;
>
> - if (!job_is_cancelled(job) && job->ret == 0) {
> - /* success */
> - job->ret = bdrv_drop_intermediate(s->commit_top_bs, base,
> - s->backing_file_str);
> - } else {
> - /* XXX Can (or should) we somehow keep 'consistent read' blocked even
> - * after the failed/cancelled commit job is gone? If we already wrote
> - * something to base, the intermediate images aren't valid any more.
> */
> - remove_commit_top_bs = true;
> + /* FIXME: bdrv_drop_intermediate treats total failures and partial
> failures
> + * identically. Further work is needed to disambiguate these cases. */
> + return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
> + s->backing_file_str);
> +}
> +
> +static void commit_abort(Job *job)
> +{
> + CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
> + BlockDriverState *top_bs = blk_bs(s->top);
> +
> + /* Make sure commit_top_bs and top stay around until bdrv_replace_node()
> */
> + bdrv_ref(top_bs);
> + bdrv_ref(s->commit_top_bs);
> +
> + if (s->base) {
> + blk_unref(s->base);
> }
>
> + /* free the blockers on the intermediate nodes so that bdrv_replace_nodes
> + * can succeed */
> + block_job_remove_all_bdrv(&s->common);
> +
> + /* If bdrv_drop_intermediate() failed (or was not invoked), remove the
> + * commit filter driver from the backing chain now. Do this as the final
> + * step so that the 'consistent read' permission can be granted.
> + *
> + * XXX Can (or should) we somehow keep 'consistent read' blocked even
> + * after the failed/cancelled commit job is gone? If we already wrote
> + * something to base, the intermediate images aren't valid any more. */
> + bdrv_child_try_set_perm(s->commit_top_bs->backing, 0, BLK_PERM_ALL,
> + &error_abort);
> + bdrv_replace_node(s->commit_top_bs, backing_bs(s->commit_top_bs),
> + &error_abort);
> +
> + bdrv_unref(s->commit_top_bs);
> + bdrv_unref(top_bs);
> +}
> +
> +static void commit_clean(Job *job)
> +{
> + CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
> +
> /* restore base open flags here if appropriate (e.g., change the base
> back
> * to r/o). These reopens do not need to be atomic, since we won't abort
> * even on failure here */
> - if (s->base_flags != bdrv_get_flags(base)) {
> - bdrv_reopen(base, s->base_flags, NULL);
> + if (s->base_flags != bdrv_get_flags(s->base_bs)) {
> + bdrv_reopen(s->base_bs, s->base_flags, NULL);
> }
> +
> g_free(s->backing_file_str);
> blk_unref(s->top);
> -
> - /* If there is more than one reference to the job (e.g. if called from
> - * job_finish_sync()), job_completed() won't free it and therefore the
> - * blockers on the intermediate nodes remain. This would cause
> - * bdrv_set_backing_hd() to fail. */
> - block_job_remove_all_bdrv(bjob);
> -
> - /* If bdrv_drop_intermediate() didn't already do that, remove the commit
> - * filter driver from the backing chain. Do this as the final step so
> that
> - * the 'consistent read' permission can be granted. */
> - if (remove_commit_top_bs) {
> - bdrv_child_try_set_perm(commit_top_bs->backing, 0, BLK_PERM_ALL,
> - &error_abort);
> - bdrv_replace_node(commit_top_bs, backing_bs(commit_top_bs),
> - &error_abort);
> - }
> -
> - bdrv_unref(commit_top_bs);
> - bdrv_unref(top);
> }
>
> static int coroutine_fn commit_run(Job *job, Error **errp)
> @@ -211,7 +218,9 @@ static const BlockJobDriver commit_job_driver = {
> .user_resume = block_job_user_resume,
> .drain = block_job_drain,
> .run = commit_run,
> - .exit = commit_exit,
> + .prepare = commit_prepare,
> + .abort = commit_abort,
> + .clean = commit_clean
> },
> };
>
> @@ -345,6 +354,7 @@ void commit_start(const char *job_id, BlockDriverState
> *bs,
> if (ret < 0) {
> goto fail;
> }
> + s->base_bs = base;
>
> /* Required permissions are already taken with block_job_add_bdrv() */
> s->top = blk_new(0, BLK_PERM_ALL);
> --
> 2.14.4
>
- Re: [Qemu-devel] [PATCH v5 08/16] tests/blockjob: replace Blockjob with Job, (continued)
- [Qemu-devel] [PATCH v5 07/16] block/stream: refactor stream to use job callbacks, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 14/16] qapi/block-stream: expose new job properties, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 16/16] blockdev: document transactional shortcomings, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 02/16] block/mirror: add block job creation flags, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 04/16] block/commit: refactor commit to use job callbacks, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 11/16] jobs: remove .exit callback, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 15/16] block/backup: qapi documentation fixup, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 13/16] qapi/block-mirror: expose new job properties, John Snow, 2018/09/06
- [Qemu-devel] [PATCH v5 12/16] qapi/block-commit: expose new job properties, John Snow, 2018/09/06
- Re: [Qemu-devel] [PATCH v5 00/16] jobs: Job Exit Refactoring Pt 2, Max Reitz, 2018/09/07