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Re: [PATCH 4/7] block: Drop detached child from ignore list

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH 4/7] block: Drop detached child from ignore list
Date: Wed, 10 Nov 2021 16:38:43 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0

04.11.2021 13:38, Hanna Reitz wrote:
bdrv_attach_child_common_abort() restores the parent's AioContext.  To
do so, the child (which was supposed to be attached, but is now detached
again by this abort handler) is added to the ignore list for the
AioContext changing functions.

However, since we modify a BDS's children list in the BdrvChildClass's
.attach and .detach handlers, the child is already effectively detached
from the parent by this point.  We do not need to put it into the ignore

Use this opportunity to clean up the empty line structure: Keep setting
the ignore list, invoking the AioContext function, and freeing the
ignore list in blocks separated by empty lines.

Signed-off-by: Hanna Reitz <hreitz@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

What comes in my mind, is that now bdrv_replace_child_noperm() is more strong in detaching.. 
But may be not enough strong: we still have link from the child to parent (child->opaque).. 
Maybe more correct for BdrvChild object to have no relation with parent after detaching. But 
than we'll need some GenericParent object (as child->class is mostly about parent, not about 
child and even not about the edge).. Now GenericParent is "included" into BdrvChild, 
which represents both GenericParent and Edge objects..

  block.c | 8 +++++---
  1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index b95f8dcf8f..6d230ad3d1 100644
--- a/block.c
+++ b/block.c
@@ -2774,14 +2774,16 @@ static void bdrv_attach_child_common_abort(void *opaque)
if (bdrv_child_get_parent_aio_context(child) != s->old_parent_ctx) {
-        GSList *ignore = g_slist_prepend(NULL, child);
+        GSList *ignore;
+ /* No need to ignore `child`, because it has been detached already */
+        ignore = NULL;
          child->klass->can_set_aio_ctx(child, s->old_parent_ctx, &ignore,
-        ignore = g_slist_prepend(NULL, child);
-        child->klass->set_aio_ctx(child, s->old_parent_ctx, &ignore);
+ ignore = NULL;
+        child->klass->set_aio_ctx(child, s->old_parent_ctx, &ignore);

Best regards,

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