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Blame SOURCES/kvm-block-commit-refactor-commit-to-use-job-callbacks.patch

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From e24c270ca2e6a0ebd01403c19703002239477243 Mon Sep 17 00:00:00 2001
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From: John Snow <jsnow@redhat.com>
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Date: Tue, 25 Sep 2018 22:34:19 +0100
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Subject: [PATCH 16/28] block/commit: refactor commit to use job callbacks
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RH-Author: John Snow <jsnow@redhat.com>
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Message-id: <20180925223431.24791-14-jsnow@redhat.com>
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Patchwork-id: 82279
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O-Subject: [RHEL8/rhel qemu-kvm PATCH 13/25] block/commit: refactor commit to use job callbacks
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Bugzilla: 1632939
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RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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Use the component callbacks; prepare, abort, and clean.
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NB: prepare is only called when the job has not yet failed;
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and abort can be called after prepare.
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complete -> prepare -> abort -> clean
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complete -> abort -> clean
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During refactor, a potential problem with bdrv_drop_intermediate
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was identified, the patched behavior is no worse than the pre-patch
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behavior, so leave a FIXME for now to be fixed in a future patch.
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Signed-off-by: John Snow <jsnow@redhat.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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Message-id: 20180906130225.5118-5-jsnow@redhat.com
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Reviewed-by: Jeff Cody <jcody@redhat.com>
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Signed-off-by: Max Reitz <mreitz@redhat.com>
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(cherry picked from commit 22dffcbec62ba918db690ed44beba4bd4e970bb9)
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Signed-off-by: John Snow <jsnow@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 block/commit.c | 92 ++++++++++++++++++++++++++++++++--------------------------
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 1 file changed, 51 insertions(+), 41 deletions(-)
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diff --git a/block/commit.c b/block/commit.c
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index c737664..b387765 100644
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--- a/block/commit.c
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+++ b/block/commit.c
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@@ -36,6 +36,7 @@ typedef struct CommitBlockJob {
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     BlockDriverState *commit_top_bs;
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     BlockBackend *top;
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     BlockBackend *base;
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+    BlockDriverState *base_bs;
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     BlockdevOnError on_error;
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     int base_flags;
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     char *backing_file_str;
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@@ -68,61 +69,67 @@ static int coroutine_fn commit_populate(BlockBackend *bs, BlockBackend *base,
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     return 0;
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 }
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-static void commit_exit(Job *job)
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+static int commit_prepare(Job *job)
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 {
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     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
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-    BlockJob *bjob = &s->common;
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-    BlockDriverState *top = blk_bs(s->top);
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-    BlockDriverState *base = blk_bs(s->base);
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-    BlockDriverState *commit_top_bs = s->commit_top_bs;
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-    bool remove_commit_top_bs = false;
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-
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-    /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
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-    bdrv_ref(top);
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-    bdrv_ref(commit_top_bs);
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     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
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      * the normal backing chain can be restored. */
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     blk_unref(s->base);
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+    s->base = NULL;
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+
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+    /* FIXME: bdrv_drop_intermediate treats total failures and partial failures
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+     * identically. Further work is needed to disambiguate these cases. */
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+    return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
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+                                  s->backing_file_str);
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+}
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-    if (!job_is_cancelled(job) && job->ret == 0) {
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-        /* success */
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-        job->ret = bdrv_drop_intermediate(s->commit_top_bs, base,
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-                                          s->backing_file_str);
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-    } else {
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-        /* XXX Can (or should) we somehow keep 'consistent read' blocked even
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-         * after the failed/cancelled commit job is gone? If we already wrote
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-         * something to base, the intermediate images aren't valid any more. */
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-        remove_commit_top_bs = true;
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+static void commit_abort(Job *job)
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+{
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+    CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
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+    BlockDriverState *top_bs = blk_bs(s->top);
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+
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+    /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
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+    bdrv_ref(top_bs);
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+    bdrv_ref(s->commit_top_bs);
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+
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+    if (s->base) {
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+        blk_unref(s->base);
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     }
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+    /* free the blockers on the intermediate nodes so that bdrv_replace_nodes
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+     * can succeed */
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+    block_job_remove_all_bdrv(&s->common);
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+
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+    /* If bdrv_drop_intermediate() failed (or was not invoked), remove the
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+     * commit filter driver from the backing chain now. Do this as the final
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+     * step so that the 'consistent read' permission can be granted.
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+     *
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+     * XXX Can (or should) we somehow keep 'consistent read' blocked even
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+     * after the failed/cancelled commit job is gone? If we already wrote
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+     * something to base, the intermediate images aren't valid any more. */
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+    bdrv_child_try_set_perm(s->commit_top_bs->backing, 0, BLK_PERM_ALL,
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+                            &error_abort);
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+    bdrv_replace_node(s->commit_top_bs, backing_bs(s->commit_top_bs),
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+                      &error_abort);
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+
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+    bdrv_unref(s->commit_top_bs);
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+    bdrv_unref(top_bs);
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+}
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+
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+static void commit_clean(Job *job)
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+{
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+    CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
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+
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     /* restore base open flags here if appropriate (e.g., change the base back
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      * to r/o). These reopens do not need to be atomic, since we won't abort
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      * even on failure here */
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-    if (s->base_flags != bdrv_get_flags(base)) {
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-        bdrv_reopen(base, s->base_flags, NULL);
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+    if (s->base_flags != bdrv_get_flags(s->base_bs)) {
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+        bdrv_reopen(s->base_bs, s->base_flags, NULL);
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     }
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+
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     g_free(s->backing_file_str);
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     blk_unref(s->top);
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-
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-    /* If there is more than one reference to the job (e.g. if called from
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-     * job_finish_sync()), job_completed() won't free it and therefore the
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-     * blockers on the intermediate nodes remain. This would cause
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-     * bdrv_set_backing_hd() to fail. */
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-    block_job_remove_all_bdrv(bjob);
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-
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-    /* If bdrv_drop_intermediate() didn't already do that, remove the commit
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-     * filter driver from the backing chain. Do this as the final step so that
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-     * the 'consistent read' permission can be granted.  */
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-    if (remove_commit_top_bs) {
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-        bdrv_child_try_set_perm(commit_top_bs->backing, 0, BLK_PERM_ALL,
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-                                &error_abort);
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-        bdrv_replace_node(commit_top_bs, backing_bs(commit_top_bs),
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-                          &error_abort);
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-    }
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-
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-    bdrv_unref(commit_top_bs);
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-    bdrv_unref(top);
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 }
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 static int coroutine_fn commit_run(Job *job, Error **errp)
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@@ -211,7 +218,9 @@ static const BlockJobDriver commit_job_driver = {
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         .user_resume   = block_job_user_resume,
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         .drain         = block_job_drain,
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         .run           = commit_run,
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-        .exit          = commit_exit,
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+        .prepare       = commit_prepare,
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+        .abort         = commit_abort,
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+        .clean         = commit_clean
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     },
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 };
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@@ -350,6 +359,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
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     if (ret < 0) {
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         goto fail;
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     }
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+    s->base_bs = base;
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     /* Required permissions are already taken with block_job_add_bdrv() */
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     s->top = blk_new(0, BLK_PERM_ALL);
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-- 
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1.8.3.1
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