From: Max Reitz <mreitz@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"qemu-block@nongnu.org" <qemu-block@nongnu.org>
Cc: Kevin Wolf <kwolf@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH v6 20/42] block/snapshot: Fix fallback
Date: Mon, 12 Aug 2019 15:06:59 +0200 [thread overview]
Message-ID: <9266d305-7290-a622-cbdc-04bc5c7bb820@redhat.com> (raw)
In-Reply-To: <ff792d97-02aa-56f6-dc2c-39c25ebad96c@virtuozzo.com>
[-- Attachment #1.1: Type: text/plain, Size: 5465 bytes --]
On 10.08.19 18:34, Vladimir Sementsov-Ogievskiy wrote:
> 09.08.2019 19:13, Max Reitz wrote:
>> If the top node's driver does not provide snapshot functionality and we
>> want to fall back to a node down the chain, we need to snapshot all
>> non-COW children. For simplicity's sake, just do not fall back if there
>> is more than one such child.
>>
>> bdrv_snapshot_goto() becomes a bit weird because we may have to redirect
>> the actual child pointer, so it only works if the fallback child is
>> bs->file or bs->backing (and then we have to find out which it is).
>>
>> Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>> block/snapshot.c | 100 +++++++++++++++++++++++++++++++++++++----------
>> 1 file changed, 79 insertions(+), 21 deletions(-)
>>
>> diff --git a/block/snapshot.c b/block/snapshot.c
>> index f2f48f926a..35403c167f 100644
>> --- a/block/snapshot.c
>> +++ b/block/snapshot.c
>> @@ -146,6 +146,32 @@ bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs,
>> return ret;
>> }
>>
>> +/**
>> + * Return the child BDS to which we can fall back if the given BDS
>> + * does not support snapshots.
>> + * Return NULL if there is no BDS to (safely) fall back to.
>> + */
>> +static BlockDriverState *bdrv_snapshot_fallback(BlockDriverState *bs)
>> +{
>> + BlockDriverState *child_bs = NULL;
>> + BdrvChild *child;
>> +
>> + QLIST_FOREACH(child, &bs->children, next) {
>> + if (child == bdrv_filtered_cow_child(bs)) {
>> + /* Ignore: COW children need not be included in snapshots */
>> + continue;
>> + }
>> +
>> + if (child_bs) {
>> + /* Cannot fall back to a single child if there are multiple */
>> + return NULL;
>> + }
>> + child_bs = child->bs;
>> + }
>> +
>> + return child_bs;
>> +}
>> +
>> int bdrv_can_snapshot(BlockDriverState *bs)
>> {
>> BlockDriver *drv = bs->drv;
>> @@ -154,8 +180,9 @@ int bdrv_can_snapshot(BlockDriverState *bs)
>> }
>>
>> if (!drv->bdrv_snapshot_create) {
>> - if (bs->file != NULL) {
>> - return bdrv_can_snapshot(bs->file->bs);
>> + BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
>> + if (fallback_bs) {
>> + return bdrv_can_snapshot(fallback_bs);
>> }
>> return 0;
>> }
>> @@ -167,14 +194,15 @@ int bdrv_snapshot_create(BlockDriverState *bs,
>> QEMUSnapshotInfo *sn_info)
>> {
>> BlockDriver *drv = bs->drv;
>> + BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
>> if (!drv) {
>> return -ENOMEDIUM;
>> }
>> if (drv->bdrv_snapshot_create) {
>> return drv->bdrv_snapshot_create(bs, sn_info);
>> }
>> - if (bs->file) {
>> - return bdrv_snapshot_create(bs->file->bs, sn_info);
>> + if (fallback_bs) {
>> + return bdrv_snapshot_create(fallback_bs, sn_info);
>> }
>> return -ENOTSUP;
>> }
>> @@ -184,6 +212,7 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
>> Error **errp)
>> {
>> BlockDriver *drv = bs->drv;
>> + BlockDriverState *fallback_bs;
>> int ret, open_ret;
>>
>> if (!drv) {
>> @@ -204,39 +233,66 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
>> return ret;
>> }
>>
>> - if (bs->file) {
>> - BlockDriverState *file;
>> - QDict *options = qdict_clone_shallow(bs->options);
>> + fallback_bs = bdrv_snapshot_fallback(bs);
>> + if (fallback_bs) {
>> + QDict *options;
>> QDict *file_options;
>> Error *local_err = NULL;
>> + bool is_backing_child;
>> + BdrvChild **child_pointer;
>> +
>> + /*
>> + * We need a pointer to the fallback child pointer, so let us
>> + * see whether the child is referenced by a field in the BDS
>> + * object.
>> + */
>> + if (fallback_bs == bs->file->bs) {
>> + is_backing_child = false;
>> + child_pointer = &bs->file;
>> + } else if (fallback_bs == bs->backing->bs) {
>> + is_backing_child = true;
>> + child_pointer = &bs->backing;
>> + } else {
>> + /*
>> + * The fallback child is not referenced by a field in the
>> + * BDS object. We cannot go on then.
>> + */
>> + error_setg(errp, "Block driver does not support snapshots");
>> + return -ENOTSUP;
>> + }
>> +
>
> Hmm.. Should not this check be included into bdrv_snapshot_fallback(), to
> work only with file and backing?
I was under the impression that this was just special code for what
turned out to be bdrv_snapshot_load_tmp() now, because it seems so
weird. (So I thought just making the restriction here wouldn’t really
be a limit.)
I was wrong. This is used when applying snapshots, so it is important.
If we make a restriction here, we should have it in all fallback code, yes.
> And could we allow fallback only for filters? Is there real usecase except filters?
> Or may be, drop fallback at all?
raw isn’t a filter driver. And rbd as a protocol supports snapshotting.
Hence the fallback code, I presume.
Max
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next prev parent reply other threads:[~2019-08-12 13:07 UTC|newest]
Thread overview: 136+ 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
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 [this message]
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
2019-12-11 12:52 ` Max Reitz
2019-12-11 15:52 ` Kevin Wolf
2019-12-11 16:12 ` Max Reitz
2019-12-11 16:35 ` 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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