From: Max Reitz <mreitz@redhat.com> To: Kevin Wolf <kwolf@redhat.com> Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>, qemu-devel@nongnu.org, qemu-block@nongnu.org Subject: Re: [Qemu-devel] [PATCH v6 14/42] block: Use CAFs when working with backing chains Date: Mon, 9 Sep 2019 16:08:23 +0200 Message-ID: <30c5d55f-b3ef-4a52-883d-93059a76b383@redhat.com> (raw) In-Reply-To: <20190909095547.GB17606@localhost.localdomain> [-- Attachment #1.1: Type: text/plain, Size: 3565 bytes --] On 09.09.19 11:55, Kevin Wolf wrote: > Am 09.09.2019 um 10:25 hat Max Reitz geschrieben: >> On 05.09.19 16:05, Kevin Wolf wrote: >>> Am 09.08.2019 um 18:13 hat Max Reitz geschrieben: >>>> Use child access functions when iterating through backing chains so >>>> filters do not break the chain. >>>> >>>> Signed-off-by: Max Reitz <mreitz@redhat.com> >>>> --- >>>> block.c | 40 ++++++++++++++++++++++++++++------------ >>>> 1 file changed, 28 insertions(+), 12 deletions(-) >>>> >>>> diff --git a/block.c b/block.c >>>> index 86b84bea21..42abbaf0ba 100644 >>>> --- a/block.c >>>> +++ b/block.c >>>> @@ -4376,7 +4376,8 @@ int bdrv_change_backing_file(BlockDriverState *bs, >>>> } >>>> >>>> /* >>>> - * Finds the image layer in the chain that has 'bs' as its backing file. >>>> + * Finds the image layer in the chain that has 'bs' (or a filter on >>>> + * top of it) as its backing file. >>>> * >>>> * active is the current topmost image. >>>> * >>>> @@ -4388,11 +4389,18 @@ int bdrv_change_backing_file(BlockDriverState *bs, >>>> BlockDriverState *bdrv_find_overlay(BlockDriverState *active, >>>> BlockDriverState *bs) >>>> { >>>> - while (active && bs != backing_bs(active)) { >>>> - active = backing_bs(active); >>>> + bs = bdrv_skip_rw_filters(bs); >>>> + active = bdrv_skip_rw_filters(active); >>> >>> This does more than the commit message says. In addition to iterating >>> through filters instead of stopping, it also changes the semantics of >>> the function to return the next non-filter on top of bs instead of the >>> next node. >> >> Which is to say the overlay. >> >> (I think we only ever use “overlay” in the COW sense.) > > I think we do, but so far also only ever for immediate COW childs, not > for skipping through intermediate node. Yes, because it’s broken so far. >>> The block jobs seem to use it only for bdrv_is_allocated_above(), which >>> should return the same thing in both cases, so the behaviour stays the >>> same. qmp_block_commit() will check op blockers on a different node now, >>> which could be a fix or a bug, I can't tell offhand. Probably the >>> blocking doesn't really work anyway. >> >> You mean that the op blocker could have been on a block job filter node >> before? I think that‘s pretty much the point of this fix; that that >> doesn’t make sense. (We didn’t have mirror_top_bs and the like at >> 058223a6e3b.) > > On the off chance that the op blocker actually works, it can't be a job > filter. I was thinking more of throttling, blkdebug etc. Well, that’s just broken altogether right now. >>> All of this should be mentioned in the commit message at least. Maybe >>> it's also worth splitting in two patches. >> >> I don’t know. The function was written when there were no filters. > > I doubt it. blkdebug is a really old filter. > >> This change would have been a no-op then. The fact that it isn’t to me >> just means that introducing filters broke it. >> >> So I don’t know what I would write. Maybe “bdrv_find_overlay() now >> actually finds the overlay, that is, it will not return a filter node. >> This is the behavior that all callers expect (because they work on COW >> backing chains).” > > Maybe just something like "In addition, filter nodes are not returned as > overlays any more. Instead, the first non-filter node on top of bs is > considered the overlay now."? Isn’t that basically the same? :-) Max [-- Attachment #2: OpenPGP digital signature --] [-- Type: application/pgp-signature, Size: 488 bytes --]
next prev parent reply index Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-09 16:13 [Qemu-devel] [PATCH v6 00/42] block: Deal with filters Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 01/42] block: Mark commit and mirror as filter drivers Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 02/42] copy-on-read: Support compressed writes Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 03/42] throttle: " Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 04/42] block: Add child access functions Max Reitz 2019-08-09 16:56 ` Eric Blake 2019-09-04 16:16 ` Kevin Wolf 2019-09-09 7:56 ` Max Reitz 2019-09-09 9:36 ` Kevin Wolf 2019-09-09 14:04 ` Max Reitz 2019-09-09 16:13 ` Kevin Wolf 2019-09-10 9:14 ` Max Reitz 2019-09-10 10:47 ` Kevin Wolf 2019-09-10 11:36 ` Max Reitz 2019-09-10 12:48 ` Kevin Wolf 2019-09-10 12:59 ` Max Reitz 2019-09-10 13:10 ` Kevin Wolf 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 05/42] block: Add chain helper functions Max Reitz 2019-08-09 17:01 ` Eric Blake 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 06/42] qcow2: Implement .bdrv_storage_child() Max Reitz 2019-08-09 17:07 ` Eric Blake 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 07/42] block: *filtered_cow_child() for *has_zero_init() Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 08/42] block: bdrv_set_backing_hd() is about bs->backing Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 09/42] block: Include filters when freezing backing chain Max Reitz 2019-08-10 13:32 ` Vladimir Sementsov-Ogievskiy 2019-08-12 12:56 ` Max Reitz 2019-09-05 13:05 ` Kevin Wolf 2019-09-09 8:02 ` Max Reitz 2019-09-09 9:40 ` Kevin Wolf 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 10/42] block: Drop bdrv_is_encrypted() Max Reitz 2019-08-10 13:42 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 11/42] block: Add bdrv_supports_compressed_writes() Max Reitz 2019-09-05 13:11 ` Kevin Wolf 2019-09-09 8:09 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 12/42] block: Use bdrv_filtered_rw* where obvious Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 13/42] block: Use CAFs in block status functions Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 14/42] block: Use CAFs when working with backing chains Max Reitz 2019-08-10 15:19 ` Vladimir Sementsov-Ogievskiy 2019-09-05 14:05 ` Kevin Wolf 2019-09-09 8:25 ` Max Reitz 2019-09-09 9:55 ` Kevin Wolf 2019-09-09 14:08 ` Max Reitz [this message] 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 15/42] block: Re-evaluate backing file handling in reopen Max Reitz 2019-08-10 16:05 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 16/42] block: Flush all children in generic code Max Reitz 2019-08-10 15:36 ` Vladimir Sementsov-Ogievskiy 2019-08-12 12:58 ` Max Reitz 2019-09-05 16:24 ` Kevin Wolf 2019-09-09 8:31 ` Max Reitz 2019-09-09 10:01 ` Kevin Wolf 2019-09-09 14:15 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 17/42] block: Use CAFs in bdrv_refresh_limits() Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 18/42] block: Use CAFs in bdrv_refresh_filename() Max Reitz 2019-08-10 16:22 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 19/42] block: Use CAF in bdrv_co_rw_vmstate() Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 20/42] block/snapshot: Fix fallback Max Reitz 2019-08-10 16:34 ` Vladimir Sementsov-Ogievskiy 2019-08-12 13:06 ` Max Reitz 2019-09-10 11:56 ` Kevin Wolf 2019-09-10 12:04 ` Max Reitz 2019-09-10 12:49 ` Kevin Wolf 2019-09-10 13:06 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 21/42] block: Use CAFs for debug breakpoints Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 22/42] block: Fix bdrv_get_allocated_file_size's fallback Max Reitz 2019-08-10 16:41 ` Vladimir Sementsov-Ogievskiy 2019-08-12 13:09 ` Max Reitz 2019-08-12 17:14 ` Vladimir Sementsov-Ogievskiy 2019-08-12 19:15 ` Max Reitz 2019-09-10 14:52 ` Kevin Wolf 2019-09-11 6:20 ` Max Reitz 2019-09-11 6:55 ` Kevin Wolf 2019-09-11 7:37 ` Max Reitz 2019-09-11 8:27 ` Kevin Wolf 2019-09-11 10:00 ` Max Reitz 2019-09-11 10:31 ` Kevin Wolf 2019-09-11 11:00 ` Max Reitz 2019-09-12 10:34 ` Kevin Wolf 2019-11-14 13:11 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 23/42] blockdev: Use CAF in external_snapshot_prepare() Max Reitz 2019-09-10 15:02 ` Kevin Wolf 2019-09-11 6:21 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 24/42] block: Use child access functions for QAPI queries Max Reitz 2019-08-10 16:57 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 25/42] mirror: Deal with filters Max Reitz 2019-08-12 11:09 ` Vladimir Sementsov-Ogievskiy 2019-08-12 13:26 ` Max Reitz 2019-08-14 15:17 ` Vladimir Sementsov-Ogievskiy 2019-08-31 9:57 ` Vladimir Sementsov-Ogievskiy 2019-09-02 14:35 ` Max Reitz 2019-09-03 8:32 ` Vladimir Sementsov-Ogievskiy 2019-09-09 7:41 ` Max Reitz 2019-09-13 12:55 ` Kevin Wolf 2019-09-16 10:26 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 26/42] backup: " Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 27/42] commit: " Max Reitz 2019-08-31 10:44 ` Vladimir Sementsov-Ogievskiy 2019-09-02 14:55 ` Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 28/42] stream: " Max Reitz 2019-08-12 11:55 ` Vladimir Sementsov-Ogievskiy 2019-09-13 14:16 ` Kevin Wolf 2019-09-16 9:52 ` Max Reitz 2019-09-16 14:47 ` Kevin Wolf 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 29/42] nbd: Use CAF when looking for dirty bitmap Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 30/42] qemu-img: Use child access functions Max Reitz 2019-08-12 12:14 ` Vladimir Sementsov-Ogievskiy 2019-08-12 13:28 ` Max Reitz 2019-08-14 16:04 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 31/42] block: Drop backing_bs() Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 32/42] block: Make bdrv_get_cumulative_perm() public Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 33/42] blockdev: Fix active commit choice Max Reitz 2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 34/42] block: Inline bdrv_co_block_status_from_*() Max Reitz 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 35/42] block: Fix check_to_replace_node() Max Reitz 2019-08-15 15:21 ` Vladimir Sementsov-Ogievskiy 2019-08-15 17:01 ` Max Reitz 2019-08-16 11:01 ` Vladimir Sementsov-Ogievskiy 2019-08-16 13:30 ` Max Reitz 2019-08-16 14:24 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 36/42] iotests: Add tests for mirror @replaces loops Max Reitz 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 37/42] block: Leave BDS.backing_file constant Max Reitz 2019-08-16 16:16 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 38/42] iotests: Let complete_and_wait() work with commit Max Reitz 2019-08-23 5:59 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 39/42] iotests: Add filter commit test cases Max Reitz 2019-08-31 11:41 ` Vladimir Sementsov-Ogievskiy 2019-09-02 15:06 ` Max Reitz 2019-08-31 12:35 ` Vladimir Sementsov-Ogievskiy 2019-09-02 15:09 ` Max Reitz 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 40/42] iotests: Add filter mirror " Max Reitz 2019-08-31 12:35 ` Vladimir Sementsov-Ogievskiy 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 41/42] iotests: Add test for commit in sub directory Max Reitz 2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 42/42] iotests: Test committing to overridden backing Max Reitz 2019-09-03 9:18 ` Vladimir Sementsov-Ogievskiy
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