On 01.10.19 16:00, Vladimir Sementsov-Ogievskiy wrote: > 01.10.2019 3:09, John Snow wrote: >> Hi folks, I identified a problem with the migration code that Red Hat QE >> found and thought you'd like to see it: >> >> https://bugzilla.redhat.com/show_bug.cgi?id=1652424#c20 >> >> Very, very briefly: drive-mirror inserts a filter node that changes what >> bdrv_get_device_or_node_name() returns, which causes a migration problem. >> >> >> Ignorant question #1: Can we multi-parent the filter node and >> source-node? It looks like at the moment both consider their only parent >> to be the block-job and don't have a link back to their parents otherwise. >> >> >> Otherwise: I have a lot of cloudy ideas on how to solve this, but >> ultimately what we want is to be able to find the "addressable" name for >> the node the bitmap is attached to, which would be the name of the first >> ancestor node that isn't a filter. (OR, the name of the block-backend >> above that node.) > > Not the name of ancestor node, it will break mapping: it must be name of the > node itself or name of parent (may be through several filters) block-backend > >> >> A simple way to do this might be a "child_unfiltered" BdrvChild role >> that simply bypasses the filter that was inserted and serves no real >> purpose other than to allow the child to have a parent link and find who >> it's """real""" parent is. >> >> Because of flushing, reopen, sync, drain &c &c &c I'm not sure how >> feasible this quick idea might be, though. >> >> >> - Corollary fix #1: call error_setg if the bitmap node name that's about >> to go over the wire is an autogenerated node: this is never correct! >> >> (Why not? because the target is incapable of matching the node-name >> because they are randomly generated AND you cannot specify node-names >> with # prefixes as they are especially reserved! >> >> (This raises a related problem: if you explicitly add bitmaps to nodes >> with autogenerated names, you will be unable to migrate them.)) >> >> --js >> > > What about the following: > > diff --git a/block.c b/block.c > index 5944124845..6739c19be9 100644 > --- a/block.c > +++ b/block.c > @@ -1009,8 +1009,20 @@ static void bdrv_inherited_options(int *child_flags, > QDict *child_options, > *child_flags = flags; > } > > +static const char *bdrv_child_get_name(BdrvChild *child) > +{ > + BlockDriverState *parent = child->opaque; > + > + if (parent->drv && parent->drv->is_filter) { > + return bdrv_get_parent_name(parent); > + } > + > + return NULL; > +} > +
Why would we skip filters explicitly added by the user? Max
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