From: Peter Krempa <pkrempa@redhat.com>
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 <pkrempa@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
---
block/monitor/block-hmp-cmds.c | 4 ++--
block/qapi.c | 9 +++++----
qapi/block-core.json | 7 +++++++
ui/cocoa.m | 2 +-
4 files changed, 15 insertions(+), 7 deletions(-)
diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index 3391cee4d2..bde25bb588 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -422,7 +422,7 @@ void hmp_nbd_server_start(Monitor *mon, const QDict *qdict)
/* Then try adding all block devices. If one fails, close all and
* exit.
*/
- block_list = qmp_query_block(NULL);
+ block_list = qmp_query_block(false, false, NULL);
for (info = block_list; info; info = info->next) {
if (!info->value->inserted) {
@@ -741,7 +741,7 @@ void hmp_info_block(Monitor *mon, const QDict *qdict)
/* Print BlockBackend information */
if (!nodes) {
- block_list = qmp_query_block(NULL);
+ block_list = qmp_query_block(false, false, NULL);
} else {
block_list = NULL;
}
diff --git a/block/qapi.c b/block/qapi.c
index 27e0ac6a32..3688d0e713 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -456,7 +456,7 @@ fail:
/* @p_info will be set only on success. */
static void GRAPH_RDLOCK
-bdrv_query_info(BlockBackend *blk, BlockInfo **p_info, Error **errp)
+bdrv_query_info(BlockBackend *blk, bool flat, BlockInfo **p_info, Error **errp)
{
BlockInfo *info = g_malloc0(sizeof(*info));
BlockDriverState *bs = blk_bs(blk);
@@ -488,7 +488,7 @@ bdrv_query_info(BlockBackend *blk, BlockInfo **p_info, Error **errp)
}
if (bs && bs->drv) {
- info->inserted = bdrv_block_device_info(blk, bs, false, errp);
+ info->inserted = bdrv_block_device_info(blk, bs, flat, errp);
if (info->inserted == NULL) {
goto err;
}
@@ -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;
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..f55cf01dca 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -855,6 +855,12 @@
#
# Get a list of `BlockInfo` for all virtual block devices.
#
+# @flat: Omit the nested data about backing image (Omitted are
+# contents of 'backing-image' key of the 'ImageInfo' struct
+# which is returned as 'image' key of 'BlockDeviceInfo' struct
+# returned as 'inserted' key in 'BlockInfo' struct returned
+# by this command). Default is false (Since 11.0)
+#
# Returns: a list describing each virtual block device. Filter nodes
# that were created implicitly are skipped over.
#
@@ -945,6 +951,7 @@
# }
##
{ 'command': 'query-block', 'returns': ['BlockInfo'],
+ 'data': { '*flat': 'bool' },
'allow-preconfig': true }
##
diff --git a/ui/cocoa.m b/ui/cocoa.m
index 23b7a736d7..5b21fe3aea 100644
--- a/ui/cocoa.m
+++ b/ui/cocoa.m
@@ -1849,7 +1849,7 @@ static void addRemovableDevicesMenuItems(void)
BlockInfoList *currentDevice, *pointerToFree;
NSString *deviceName;
- currentDevice = qmp_query_block(NULL);
+ currentDevice = qmp_query_block(false, false, NULL);
pointerToFree = currentDevice;
menu = [[[NSApp mainMenu] itemWithTitle:@"Machine"] submenu];
--
2.52.0On Tue, Jan 20, 2026 at 03:45:56PM +0100, Peter Krempa wrote:
> From: Peter Krempa <pkrempa@redhat.com>
>
> 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 <pkrempa@redhat.com>
> Acked-by: Markus Armbruster <armbru@redhat.com>
> ---
> block/monitor/block-hmp-cmds.c | 4 ++--
> block/qapi.c | 9 +++++----
> qapi/block-core.json | 7 +++++++
> ui/cocoa.m | 2 +-
> 4 files changed, 15 insertions(+), 7 deletions(-)
> +++ b/qapi/block-core.json
> @@ -855,6 +855,12 @@
> #
> # Get a list of `BlockInfo` for all virtual block devices.
> #
> +# @flat: Omit the nested data about backing image (Omitted are
> +# contents of 'backing-image' key of the 'ImageInfo' struct
> +# which is returned as 'image' key of 'BlockDeviceInfo' struct
> +# returned as 'inserted' key in 'BlockInfo' struct returned
Extra space.
> +# by this command). Default is false (Since 11.0)
Still hard to parse. Maybe:
@flat: Omit nested data about the backing image (ie. the contents at
'inserted.image.backing-image' are trimmed to avoid duplicate
data about that backing image). Default is false (Since 11.0)
The idea makes sense to me, but I will defer to Markus on whether the
wording still needs a tweak.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
On Mon, Jan 26, 2026 at 13:27:33 -0600, Eric Blake wrote:
> On Tue, Jan 20, 2026 at 03:45:56PM +0100, Peter Krempa wrote:
> > From: Peter Krempa <pkrempa@redhat.com>
> >
> > 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 <pkrempa@redhat.com>
> > Acked-by: Markus Armbruster <armbru@redhat.com>
> > ---
> > block/monitor/block-hmp-cmds.c | 4 ++--
> > block/qapi.c | 9 +++++----
> > qapi/block-core.json | 7 +++++++
> > ui/cocoa.m | 2 +-
> > 4 files changed, 15 insertions(+), 7 deletions(-)
> > +++ b/qapi/block-core.json
> > @@ -855,6 +855,12 @@
> > #
> > # Get a list of `BlockInfo` for all virtual block devices.
> > #
> > +# @flat: Omit the nested data about backing image (Omitted are
> > +# contents of 'backing-image' key of the 'ImageInfo' struct
> > +# which is returned as 'image' key of 'BlockDeviceInfo' struct
> > +# returned as 'inserted' key in 'BlockInfo' struct returned
>
> Extra space.
>
> > +# by this command). Default is false (Since 11.0)
>
> Still hard to parse. Maybe:
>
> @flat: Omit nested data about the backing image (ie. the contents at
> 'inserted.image.backing-image' are trimmed to avoid duplicate
> data about that backing image). Default is false (Since 11.0)
In this case the 'backing-image' data is not duplicate as it was the
case with 'query-named-block-nodes', as it is not repeated on top level.
Here using 'flat' decreases the amount of returned information, but in
case of libvirt we don't use anything from the 'backing-image', just
stuff that is related to the frontend device which is not queryable via
'query-named-block-nodes'.
So then perhaps just shorten it to:
@flat: Omit nested data about the backing image (ie. the contents at
'inserted.image.backing-image' are trimmed).
Default is false (Since 11.0)
> The idea makes sense to me, but I will defer to Markus on whether the
> wording still needs a tweak.
Should I post a v3?
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