Re: [Qemu-devel] [PATCH v6 25/42] mirror: Deal with filters

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

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 <mreitz@redhat.com>
> ---
>   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.

> +        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>

> +        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)".

> +                 */
> +                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?

> +        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;
> +        }
>           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 ?

> 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