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Re: [Qemu-devel] [PATCH v6 25/42] mirror: Deal with filters
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From: |
Vladimir Sementsov-Ogievskiy |
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Subject: |
Re: [Qemu-devel] [PATCH v6 25/42] mirror: Deal with filters |
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Date: |
Tue, 3 Sep 2019 08:32:50 +0000 |
02.09.2019 17:35, Max Reitz wrote:
> On 31.08.19 11:57, Vladimir Sementsov-Ogievskiy wrote:
>> 09.08.2019 19:13, Max Reitz wrote:
>>> This includes some permission limiting (for example, we only need to
>>> take the RESIZE permission for active commits where the base is smaller
>>> than the top).
>>>
>>> Signed-off-by: Max Reitz <address@hidden>
>>> ---
>>> block/mirror.c | 117 ++++++++++++++++++++++++++++++++++++++-----------
>>> blockdev.c | 47 +++++++++++++++++---
>>> 2 files changed, 131 insertions(+), 33 deletions(-)
>>>
>>> diff --git a/block/mirror.c b/block/mirror.c
>>> index 54bafdf176..6ddbfb9708 100644
>>> --- a/block/mirror.c
>>> +++ b/block/mirror.c
>>> @@ -42,6 +42,7 @@ typedef struct MirrorBlockJob {
>>> BlockBackend *target;
>>> BlockDriverState *mirror_top_bs;
>>> BlockDriverState *base;
>>> + BlockDriverState *base_overlay;
>>>
>>> /* The name of the graph node to replace */
>>> char *replaces;
>>> @@ -665,8 +666,10 @@ static int mirror_exit_common(Job *job)
>>> &error_abort);
>>> if (!abort && s->backing_mode == MIRROR_SOURCE_BACKING_CHAIN) {
>>> BlockDriverState *backing = s->is_none_mode ? src : s->base;
>>> - if (backing_bs(target_bs) != backing) {
>>> - bdrv_set_backing_hd(target_bs, backing, &local_err);
>>> + BlockDriverState *unfiltered_target =
>>> bdrv_skip_rw_filters(target_bs);
>>> +
>>> + if (bdrv_filtered_cow_bs(unfiltered_target) != backing) {
>>> + bdrv_set_backing_hd(unfiltered_target, backing, &local_err);
>>> if (local_err) {
>>> error_report_err(local_err);
>>> ret = -EPERM;
>>> @@ -715,7 +718,7 @@ static int mirror_exit_common(Job *job)
>>> * valid.
>>> */
>>> block_job_remove_all_bdrv(bjob);
>>> - bdrv_replace_node(mirror_top_bs, backing_bs(mirror_top_bs),
>>> &error_abort);
>>> + bdrv_replace_node(mirror_top_bs, mirror_top_bs->backing->bs,
>>> &error_abort);
>>>
>>> /* We just changed the BDS the job BB refers to (with either or both
>>> of the
>>> * bdrv_replace_node() calls), so switch the BB back so the cleanup
>>> does
>>> @@ -812,7 +815,8 @@ static int coroutine_fn
>>> mirror_dirty_init(MirrorBlockJob *s)
>>> return 0;
>>> }
>>>
>>> - ret = bdrv_is_allocated_above(bs, base, false, offset, bytes,
>>> &count);
>>> + ret = bdrv_is_allocated_above(bs, s->base_overlay, true, offset,
>>> bytes,
>>> + &count);
>>> if (ret < 0) {
>>> return ret;
>>> }
>>> @@ -908,7 +912,7 @@ static int coroutine_fn mirror_run(Job *job, Error
>>> **errp)
>>> } else {
>>> s->target_cluster_size = BDRV_SECTOR_SIZE;
>>> }
>>> - if (backing_filename[0] && !target_bs->backing &&
>>> + if (backing_filename[0] && !bdrv_backing_chain_next(target_bs) &&
>>> s->granularity < s->target_cluster_size) {
>>> s->buf_size = MAX(s->buf_size, s->target_cluster_size);
>>> s->cow_bitmap = bitmap_new(length);
>>> @@ -1088,8 +1092,9 @@ static void mirror_complete(Job *job, Error **errp)
>>> if (s->backing_mode == MIRROR_OPEN_BACKING_CHAIN) {
>>> int ret;
>>>
>>> - assert(!target->backing);
>>> - ret = bdrv_open_backing_file(target, NULL, "backing", errp);
>>> + assert(!bdrv_backing_chain_next(target));
>>
>> Preexisting, but seems we may crash here, I don't see where it is checked
>> before, to
>> return error if there is some backing. And even if we do so, we don't
>> prevent appearing
>> of target backing during mirror operation.
>
> The idea is that MIRROR_OPEN_BACKING_CHAIN is set only when using
> drive-mirror with mode=existing. In this case, we also set
> BDRV_O_NO_BACKING for the target.
>
> You’re right that a user could add a backing chain to the target during
> the operation. They really have to make an effort to shoot themselves
> in the foot for this because the target must have an auto-generated node
> name.
>
> I suppose the best would be not to open the backing chain if the target
> node already has a backing child?
Hmm, but we still should generate an error, as we can't do what was requested.
>
>>> + ret = bdrv_open_backing_file(bdrv_skip_rw_filters(target), NULL,
>>> + "backing", errp);
>>> if (ret < 0) {
>>> return;
>>> }
>>> @@ -1531,8 +1536,8 @@ static BlockJob *mirror_start_job(
>>> MirrorBlockJob *s;
>>> MirrorBDSOpaque *bs_opaque;
>>> BlockDriverState *mirror_top_bs;
>>> - bool target_graph_mod;
>>> bool target_is_backing;
>>> + uint64_t target_perms, target_shared_perms;
>>> Error *local_err = NULL;
>>> int ret;
>>>
>>> @@ -1551,7 +1556,7 @@ static BlockJob *mirror_start_job(
>>> buf_size = DEFAULT_MIRROR_BUF_SIZE;
>>> }
>>>
>>> - if (bs == target) {
>>> + if (bdrv_skip_rw_filters(bs) == bdrv_skip_rw_filters(target)) {
>>> error_setg(errp, "Can't mirror node into itself");
>>> return NULL;
>>> }
>>> @@ -1615,15 +1620,50 @@ static BlockJob *mirror_start_job(
>>> * In the case of active commit, things look a bit different, though,
>>> * because the target is an already populated backing file in active
>>> use.
>>> * We can allow anything except resize there.*/
>>> +
>>> + target_perms = BLK_PERM_WRITE;
>>> + target_shared_perms = BLK_PERM_WRITE_UNCHANGED;
>>> +
>>> target_is_backing = bdrv_chain_contains(bs, target);
>>> - target_graph_mod = (backing_mode != MIRROR_LEAVE_BACKING_CHAIN);
>>> + if (target_is_backing) {
>>> + int64_t bs_size, target_size;
>>
>> <empty after definitions>
>
> Is that part of any of our guidelines? :-)
>
> Sure, will add.
Not sure. Someone asked me about it on list in past and I'm used to.
>
>>> + bs_size = bdrv_getlength(bs);
>>> + if (bs_size < 0) {
>>> + error_setg_errno(errp, -bs_size,
>>> + "Could not inquire top image size");
>>> + goto fail;
>>> + }
>>> +
>>> + target_size = bdrv_getlength(target);
>>> + if (target_size < 0) {
>>> + error_setg_errno(errp, -target_size,
>>> + "Could not inquire base image size");
>>> + goto fail;
>>> + }
>>> +
>>> + if (target_size < bs_size) {
>>> + target_perms |= BLK_PERM_RESIZE;
>>> + }
>>> +
>>> + target_shared_perms |= BLK_PERM_CONSISTENT_READ
>>> + | BLK_PERM_WRITE
>>> + | BLK_PERM_GRAPH_MOD;
>>> + } else if (bdrv_chain_contains(bs, bdrv_skip_rw_filters(target))) {
>>> + /*
>>> + * We may want to allow this in the future, but it would
>>> + * require taking some extra care.
>>> + */
>>> + error_setg(errp, "Cannot mirror to a filter on top of a node in
>>> the "
>>> + "source's backing chain");
>>> + goto fail;
>>> + }
>>> +
>>> + if (backing_mode != MIRROR_LEAVE_BACKING_CHAIN) {
>>> + target_perms |= BLK_PERM_GRAPH_MOD;
>>> + }
>>> +
>>> s->target = blk_new(s->common.job.aio_context,
>>> - BLK_PERM_WRITE | BLK_PERM_RESIZE |
>>> - (target_graph_mod ? BLK_PERM_GRAPH_MOD : 0),
>>> - BLK_PERM_WRITE_UNCHANGED |
>>> - (target_is_backing ? BLK_PERM_CONSISTENT_READ |
>>> - BLK_PERM_WRITE |
>>> - BLK_PERM_GRAPH_MOD : 0));
>>> + target_perms, target_shared_perms);
>>> ret = blk_insert_bs(s->target, target, errp);
>>> if (ret < 0) {
>>> goto fail;
>>> @@ -1647,6 +1687,7 @@ static BlockJob *mirror_start_job(
>>> s->backing_mode = backing_mode;
>>> s->copy_mode = copy_mode;
>>> s->base = base;
>>> + s->base_overlay = bdrv_find_overlay(bs, base);
>>> s->granularity = granularity;
>>> s->buf_size = ROUND_UP(buf_size, granularity);
>>> s->unmap = unmap;
>>> @@ -1693,15 +1734,39 @@ static BlockJob *mirror_start_job(
>>> /* In commit_active_start() all intermediate nodes disappear, so
>>> * any jobs in them must be blocked */
>>> if (target_is_backing) {
>>> - BlockDriverState *iter;
>>> - for (iter = backing_bs(bs); iter != target; iter =
>>> backing_bs(iter)) {
>>> - /* XXX BLK_PERM_WRITE needs to be allowed so we don't block
>>> - * ourselves at s->base (if writes are blocked for a node,
>>> they are
>>> - * also blocked for its backing file). The other options would
>>> be a
>>> - * second filter driver above s->base (== target). */
>>> + BlockDriverState *iter, *filtered_target;
>>> + uint64_t iter_shared_perms;
>>> +
>>> + /*
>>> + * The topmost node with
>>> + * bdrv_skip_rw_filters(filtered_target) ==
>>> bdrv_skip_rw_filters(target)
>>> + */
>>> + filtered_target = bdrv_filtered_cow_bs(bdrv_find_overlay(bs,
>>> target));
>>> +
>>> + assert(bdrv_skip_rw_filters(filtered_target) ==
>>> + bdrv_skip_rw_filters(target));
>>> +
>>> + /*
>>> + * XXX BLK_PERM_WRITE needs to be allowed so we don't block
>>> + * ourselves at s->base (if writes are blocked for a node, they are
>>> + * also blocked for its backing file). The other options would be a
>>> + * second filter driver above s->base (== target).
>>> + */
>>> + iter_shared_perms = BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE;
>>> +
>>> + for (iter = bdrv_filtered_bs(bs); iter != target;
>>> + iter = bdrv_filtered_bs(iter))
>>> + {
>>> + if (iter == filtered_target) {
>>> + /*
>>> + * From here on, all nodes are filters on the base.
>>> + * This allows us to share BLK_PERM_CONSISTENT_READ.
>>
>> I'd prefere to add something like: "because we share it on target (see
>> target BlockBackend creation
>> and corresponding comment above)".
>
> I’d rather not refer to other comments in case they change… Maybe just
> “This allows us to share BLK_PERM_CONSISTENT_READ, as we do on the
> target.”? I think if someone is interested, they will scan the file for
> what permissions are shared on the target anyway.
OK. Yes I just wanted to stress that we just duplicate behavior about target,
as it helped
me to understand.
>
>>> + */
>>> + iter_shared_perms |= BLK_PERM_CONSISTENT_READ;
>>> + }
>>> +
>>> ret = block_job_add_bdrv(&s->common, "intermediate node",
>>> iter, 0,
>>> - BLK_PERM_WRITE_UNCHANGED |
>>> BLK_PERM_WRITE,
>>> - errp);
>>> + iter_shared_perms, errp);
>>> if (ret < 0) {
>>> goto fail;
>>> }
>>> @@ -1737,7 +1802,7 @@ fail:
>>> bs_opaque->stop = true;
>>> bdrv_child_refresh_perms(mirror_top_bs, mirror_top_bs->backing,
>>> &error_abort);
>>> - bdrv_replace_node(mirror_top_bs, backing_bs(mirror_top_bs),
>>> &error_abort);
>>> + bdrv_replace_node(mirror_top_bs, mirror_top_bs->backing->bs,
>>> &error_abort);
>>>
>>> bdrv_unref(mirror_top_bs);
>>>
>>> @@ -1764,7 +1829,7 @@ void mirror_start(const char *job_id,
>>> BlockDriverState *bs,
>>> return;
>>> }
>>> is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
>>> - base = mode == MIRROR_SYNC_MODE_TOP ? backing_bs(bs) : NULL;
>>> + base = mode == MIRROR_SYNC_MODE_TOP ? bdrv_backing_chain_next(bs) :
>>> NULL;
>>> mirror_start_job(job_id, bs, creation_flags, target, replaces,
>>> speed, granularity, buf_size, backing_mode,
>>> on_source_error, on_target_error, unmap, NULL, NULL,
>>> diff --git a/blockdev.c b/blockdev.c
>>> index c540802127..c451f553f7 100644
>>
>>
>> block/mirroc.c is OK for me. Continue with blockdev.c...
>>
>>> --- a/blockdev.c
>>> +++ b/blockdev.c
>>> @@ -3851,7 +3851,7 @@ static void blockdev_mirror_common(const char
>>> *job_id, BlockDriverState *bs,
>>> return;
>>> }
>>>
>>> - if (!bs->backing && sync == MIRROR_SYNC_MODE_TOP) {
>>> + if (!bdrv_backing_chain_next(bs) && sync == MIRROR_SYNC_MODE_TOP) {
>>> sync = MIRROR_SYNC_MODE_FULL;
>>> }
>>>
>>> @@ -3900,7 +3900,7 @@ static void blockdev_mirror_common(const char
>>> *job_id, BlockDriverState *bs,
>>>
>>> void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> {
>>> - BlockDriverState *bs;
>>> + BlockDriverState *bs, *unfiltered_bs;
>>> BlockDriverState *source, *target_bs;
>>> AioContext *aio_context;
>>> BlockMirrorBackingMode backing_mode;
>>> @@ -3909,6 +3909,7 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> int flags;
>>> int64_t size;
>>> const char *format = arg->format;
>>> + const char *replaces_node_name = NULL;
>>> int ret;
>>>
>>> bs = qmp_get_root_bs(arg->device, errp);
>>> @@ -3921,6 +3922,16 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> return;
>>> }
>>>
>>> + /*
>>> + * If the user has not instructed us otherwise, we should let the
>>> + * block job run from @bs (thus taking into account all filters on
>>> + * it) but replace @unfiltered_bs when it finishes (thus not
>>> + * removing those filters).
>>> + * (And if there are any explicit filters, we should assume the
>>> + * user knows how to use the @replaces option.)
>>> + */
>>> + unfiltered_bs = bdrv_skip_implicit_filters(bs);
>>> +
>>> aio_context = bdrv_get_aio_context(bs);
>>> aio_context_acquire(aio_context);
>>>
>>> @@ -3934,8 +3945,14 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> }
>>>
>>> flags = bs->open_flags | BDRV_O_RDWR;
>>> - source = backing_bs(bs);
>>> + source = bdrv_filtered_cow_bs(unfiltered_bs);
>>> if (!source && arg->sync == MIRROR_SYNC_MODE_TOP) {
>>
>>
>> Hmm, you handle this case a bit differently here and in
>> blockdev_mirror_common..
>> Can we handle it only in blockdev_mirror_common, to be consistent with
>> qmp_blockdev_mirror?
>
> What exactly do you mean? The difference between skipping all filters
> and just skipping implicit filters? Hm.
>
> First, the check in blockdev_mirror_common() should actually be
> unnecessary. In qmp_{blockdev,drive}_mirror(), we do nearly the same
> check anyway (and then force sync=full if there is no backing file).
Hmm, I see it only in qmp_drive_mirror, not in _blockdev_
> So
> if all three functions did the same check, we wouldn’t need it in
> blockdev_mirror_common().
And if it was so, better have one check in _common than two duplicated.
>
> Second, let’s look at the difference in an example: One where
> blockdev_mirror_common() would not decide to enforce mode=full, but
> qmp_{blockdev,drive}_mirror() would.
> This happens when @bs is an explicit filter over some overlay with a
> backing file, e.g.:
>
> throttle --file--> qcow2 --backing--> raw
>
> It’s correct to run the mirror job from the throttle node; but @source
> should be bdrv_backing_chain_next() so it will point to the raw node.
> Currently, it is NULL (because the throttle node does not have a COW child).
>
> But then again, I’ve made qmp_{blockdev,drive}_mirror() throw an error
> in such a case:
>
>>> + if (bdrv_filtered_bs(unfiltered_bs)) {
>>> + /* @unfiltered_bs is an explicit filter */
>>> + error_setg(errp, "Cannot perform sync=top mirror through an "
>>> + "explicitly added filter node on the source");
>>> + goto out;
>>> + }
>
> So it isn’t really a problem. Still, does the error make sense? Should
> we just allow that case by letting source be
> bdrv_filtered_cow_bs(bdrv_skip_rw_filters(bs))?
Looks good. As I understand, you have the test (40/42) for this case and it
works for _blockdev_ and for for _drive_ version of command. Of course, they'd
better behave in same manner.
>
> (BTW, I just noticed that @base seems to be pretty much unused in
> block/mirror.c. It only really uses @base_overlay now. So I suppose it
> makes sense to remove it in v7.)
>
>>> arg->sync = MIRROR_SYNC_MODE_FULL;
>>> }
>>> if (arg->sync == MIRROR_SYNC_MODE_NONE) {
>>> @@ -3954,6 +3971,9 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> " named node of the graph");
>>> goto out;
>>> }
>>> + replaces_node_name = arg->replaces;
>>> + } else if (unfiltered_bs != bs) {
>>> + replaces_node_name = unfiltered_bs->node_name;
>>> }
>>>
>>> if (arg->mode == NEW_IMAGE_MODE_ABSOLUTE_PATHS) {
>>> @@ -3973,6 +3993,9 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> bdrv_img_create(arg->target, format,
>>> NULL, NULL, NULL, size, flags, false,
>>> &local_err);
>>> } else {
>>> + /* Implicit filters should not appear in the filename */
>>> + BlockDriverState *explicit_backing =
>>> bdrv_skip_implicit_filters(source);
>>> +
>>> switch (arg->mode) {
>>> case NEW_IMAGE_MODE_EXISTING:
>>> break;
>>> @@ -3980,8 +4003,8 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> /* create new image with backing file */
>>> bdrv_refresh_filename(source);
>>> bdrv_img_create(arg->target, format,
>>> - source->filename,
>>> - source->drv->format_name,
>>> + explicit_backing->filename,
>>> + explicit_backing->drv->format_name,
>>> NULL, size, flags, false, &local_err);
>>> break;
>>> default:
>>> @@ -4017,7 +4040,7 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>>> }
>>>
>>> blockdev_mirror_common(arg->has_job_id ? arg->job_id : NULL, bs,
>>> target_bs,
>>> - arg->has_replaces, arg->replaces, arg->sync,
>>> + !!replaces_node_name, replaces_node_name,
>>> arg->sync,
>>> backing_mode, arg->has_speed, arg->speed,
>>> arg->has_granularity, arg->granularity,
>>> arg->has_buf_size, arg->buf_size,
>>> @@ -4053,7 +4076,7 @@ void qmp_blockdev_mirror(bool has_job_id, const char
>>> *job_id,
>>> bool has_auto_dismiss, bool auto_dismiss,
>>> Error **errp)
>>> {
>>> - BlockDriverState *bs;
>>> + BlockDriverState *bs, *unfiltered_bs;
>>> BlockDriverState *target_bs;
>>> AioContext *aio_context;
>>> BlockMirrorBackingMode backing_mode = MIRROR_LEAVE_BACKING_CHAIN;
>>> @@ -4065,6 +4088,16 @@ void qmp_blockdev_mirror(bool has_job_id, const char
>>> *job_id,
>>> return;
>>> }
>>>
>>> + /*
>>> + * Same as in qmp_drive_mirror():
>>
>> Then, may be better do it in blockdev_mirror_common ?
>
> Hm, maybe. Should we decide to let @source be
> bdrv_filtered_cow_bs(bdrv_skip_rw_filters(bs)) in qmp_drive_mirror(), I
> don’t think we need @unfiltered_bs there to determine @source.
>
> Max
>
>>> We want to run the job from @bs,
>>> + * but we want to replace @unfiltered_bs on completion.
>>> + */
>>> + unfiltered_bs = bdrv_skip_implicit_filters(bs);
>>> + if (!has_replaces && unfiltered_bs != bs) {
>>> + replaces = unfiltered_bs->node_name;
>>> + has_replaces = true;
>>> + }
>>> +
>>> target_bs = bdrv_lookup_bs(target, target, errp);
>>> if (!target_bs) {
>>> return;
>>>
>>
>>
>
>
--
Best regards,
Vladimir