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
> Reviewed-by: Max Reitz
Reviewed-by: Jeff Cody
> ---
> 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 = >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(>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,
> +_abort);
> +bdrv_replace_node(s->commit_top_bs, backing_bs(s->commit_top_bs),
> + _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. */
>
