From 5bb047477807375e2d5e2494b1d1302d5cea4b73 Mon Sep 17 00:00:00 2001 From: Vladimir Sementsov-Ogievskiy Date: Tue, 26 Jul 2022 23:11:32 +0300 Subject: block: Manipulate bs->file / bs->backing pointers in .attach/.detach bs->file and bs->backing are a kind of duplication of part of bs->children. But very useful diplication, so let's not drop them at all:) We should manage bs->file and bs->backing in same place, where we manage bs->children, to keep them in sync. Moreover, generic io paths are unprepared to BdrvChild without a bs, so it's double good to clear bs->file / bs->backing when we detach the child. Detach is simple: if we detach bs->file or bs->backing child, just set corresponding field to NULL. Attach is a bit more complicated. But we still can precisely detect should we set one of bs->file / bs->backing or not: - if role is BDRV_CHILD_COW, we definitely deal with bs->backing - else, if role is BDRV_CHILD_FILTERED (it must be also BDRV_CHILD_PRIMARY), it's a filtered child. Use bs->drv->filtered_child_is_backing to chose the pointer field to modify. - else, if role is BDRV_CHILD_PRIMARY, we deal with bs->file - in all other cases, it's neither bs->backing nor bs->file. It's some other child and we shouldn't care OK. This change brings one more good thing: we can (and should) get rid of all indirect pointers in the block-graph-change transactions: bdrv_attach_child_common() stores BdrvChild** into transaction to clear it on abort. bdrv_attach_child_common() has two callers: bdrv_attach_child_noperm() just pass-through this feature, bdrv_root_attach_child() doesn't need the feature. Look at bdrv_attach_child_noperm() callers: - bdrv_attach_child() doesn't need the feature - bdrv_set_file_or_backing_noperm() uses the feature to manage bs->file and bs->backing, we don't want it anymore - bdrv_append() uses the feature to manage bs->backing, again we don't want it anymore So, we should drop this stuff! Great! We could probably keep BdrvChild** argument to keep the int return value, but it seems not worth the complexity. Finally, we now set .file / .backing automatically in generic code and want to restring setting them by hand outside of .attach/.detach. So, this patch cleanups all remaining places where they were set. To find such places I use: git grep '\->file =' git grep '\->backing =' git grep '&.*\' git grep '&.*\' Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Message-Id: <20220726201134.924743-14-vsementsov@yandex-team.ru> Signed-off-by: Kevin Wolf --- tests/unit/test-bdrv-drain.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'tests') diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c index 84e09d7070..0eecf14310 100644 --- a/tests/unit/test-bdrv-drain.c +++ b/tests/unit/test-bdrv-drain.c @@ -1830,9 +1830,8 @@ static void test_drop_intermediate_poll(void) for (i = 0; i < 3; i++) { if (i) { /* Takes the reference to chain[i - 1] */ - chain[i]->backing = bdrv_attach_child(chain[i], chain[i - 1], - "chain", &chain_child_class, - BDRV_CHILD_COW, &error_abort); + bdrv_attach_child(chain[i], chain[i - 1], "chain", + &chain_child_class, BDRV_CHILD_COW, &error_abort); } } @@ -2050,9 +2049,8 @@ static void do_test_replace_child_mid_drain(int old_drain_count, new_child_bs->total_sectors = 1; bdrv_ref(old_child_bs); - parent_bs->backing = bdrv_attach_child(parent_bs, old_child_bs, "child", - &child_of_bds, BDRV_CHILD_COW, - &error_abort); + bdrv_attach_child(parent_bs, old_child_bs, "child", &child_of_bds, + BDRV_CHILD_COW, &error_abort); for (i = 0; i < old_drain_count; i++) { bdrv_drained_begin(old_child_bs); -- cgit v1.2.3