From e24c270ca2e6a0ebd01403c19703002239477243 Mon Sep 17 00:00:00 2001

From: John Snow <jsnow@redhat.com>

Date: Tue, 25 Sep 2018 22:34:19 +0100

Subject: [PATCH 16/28] block/commit: refactor commit to use job callbacks

RH-Author: John Snow <jsnow@redhat.com>

Message-id: <20180925223431.24791-14-jsnow@redhat.com>

Patchwork-id: 82279

O-Subject: [RHEL8/rhel qemu-kvm PATCH 13/25] block/commit: refactor commit to use job callbacks

Bugzilla: 1632939

RH-Acked-by: Jeffrey Cody <jcody@redhat.com>

RH-Acked-by: Max Reitz <mreitz@redhat.com>

RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

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>

(cherry picked from commit 22dffcbec62ba918db690ed44beba4bd4e970bb9)

Signed-off-by: John Snow <jsnow@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 block/commit.c | 92 ++++++++++++++++++++++++++++++++--------------------------

 1 file changed, 51 insertions(+), 41 deletions(-)

diff --git a/block/commit.c b/block/commit.c

index c737664..b387765 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;

+

+    /* 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);

+}

-    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;

+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

     },

 };

@@ -350,6 +359,7 @@ 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);

-- 

1.8.3.1