On Tue, Feb 03, 2026 at 13:01:01 +0100, Markus Armbruster wrote:
> Peter Krempa <[email protected]> writes:
>
> > From: Peter Krempa <[email protected]>
> >
> > Some time ago (commit facda5443f5a8) I've added 'flat' mode (which
> > omits 'backing-image' key in reply) to 'query-named-block-nodes' to
> > minimize the size of the returned JSON for deeper backing chains.
> >
> > While 'query-block' behaved slightly better it turns out that in libvirt
> > we do call 'query-block' to figure out some information about the
> > block device (e.g. throttling info) but we don't look at the backing
> > chain itself.
> >
> > Wire up 'flat' for 'query-block' so that libvirt can ask for an
> > abbreviated output. The implementation is much simpler as the internals
> > are shared with 'query-named-block-nodes'.
> >
> > Signed-off-by: Peter Krempa <[email protected]>
> > Acked-by: Markus Armbruster <[email protected]>
>
> [...]
>
> > diff --git a/block/qapi.c b/block/qapi.c
> > index 27e0ac6a32..3688d0e713 100644
> > --- a/block/qapi.c
> > +++ b/block/qapi.c
>
> [...]
>
> > @@ -698,11 +698,12 @@ bdrv_query_bds_stats(BlockDriverState *bs, bool
> > blk_level)
> > return s;
> > }
> >
> > -BlockInfoList *qmp_query_block(Error **errp)
> > +BlockInfoList *qmp_query_block(bool has_flat, bool flat, Error **errp)
> > {
> > BlockInfoList *head = NULL, **p_next = &head;
> > BlockBackend *blk;
> > Error *local_err = NULL;
> > + bool return_flat = has_flat && flat;
>
> This is fine. Just flat would also be fine: flat implies has_flat.
I've borrowed this from my old patch that added it to
query-named-block-nodes.
Otherwise I'd have to mark 'has_flat' as unused. Nice side effect would
be that 'flat' can then be used directly in the call to bdrv_query_info.
Alternatively I can move the 'has_flat && flat' expression into the
arguments of the call to bdrv_query_info to avoid the extra local
variable.
Whichever you prefer.
>
> >
> > GRAPH_RDLOCK_GUARD_MAINLOOP();
> >
> > @@ -714,7 +715,7 @@ BlockInfoList *qmp_query_block(Error **errp)
> > }
> >
> > info = g_malloc0(sizeof(*info));
> > - bdrv_query_info(blk, &info->value, &local_err);
> > + bdrv_query_info(blk, return_flat, &info->value, &local_err);
> > if (local_err) {
> > error_propagate(errp, local_err);
> > g_free(info);
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index b82af74256..a701f6bbee 100644
> > --- a/qapi/block-core.json
> > +++ b/qapi/block-core.json
> > @@ -855,6 +855,10 @@
> > #
> > # Get a list of `BlockInfo` for all virtual block devices.
> > #
> > +# @flat: Omit nested data about the backing image (ie. the contents at
> > +# 'inserted.image.backing-image' are trimmed).
> > +# Default is false (Since 11.0)
> > +#
>
> s/ie./i.e./
>
> Remind me: true suppresses member inserted.image.backing-image, i.e. it
> is absent then. Correct?
Yes the 'backing-image' key is completely missing when @flat is true.
