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block/commit: refactor commit to use job callbacks

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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 <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20180906130225.5118-5-jsnow@redhat.com
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
John Snow 2018-09-06 09:02:13 -04:00 committed by Max Reitz
parent cf6320df58
commit 22dffcbec6
1 changed files with 51 additions and 41 deletions
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92
block/commit.c
View file

@ -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);