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 | 5 +++++
ui/cocoa.m | 2 +-
4 files changed, 13 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..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)
+#
# Returns: a list describing each virtual block device. Filter nodes
# that were created implicitly are skipped over.
#
@@ -945,6 +949,7 @@
# }
##
{ '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];
--
2.52.0Peter Krempa <pkrempa@redhat.com> writes:
> 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>
[...]
> 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.
>
> 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?
> # Returns: a list describing each virtual block device. Filter nodes
> # that were created implicitly are skipped over.
> #
> @@ -945,6 +949,7 @@
> # }
> ##
> { 'command': 'query-block', 'returns': ['BlockInfo'],
> + 'data': { '*flat': 'bool' },
> 'allow-preconfig': true }
>
> ##
[...]
On Tue, Feb 03, 2026 at 13:01:01 +0100, Markus Armbruster wrote:
> Peter Krempa <pkrempa@redhat.com> writes:
>
> > 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>
>
> [...]
>
> > 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.
Peter Krempa <pkrempa@redhat.com> writes:
> On Tue, Feb 03, 2026 at 13:01:01 +0100, Markus Armbruster wrote:
>> Peter Krempa <pkrempa@redhat.com> writes:
>>
>> > 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>
>>
>> [...]
>>
>> > 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.
Verbose version: This is a QMP command handler. The generated
unmarshaler passes has_flat=false, flat=false when @flat is absent, and
has_flat=true, flat=F when @flat is present with value F. Therefore,
flat can only be true when has_flat is also true. Therefore, flat
implies has_flat.
Other code calling QMP command handlers (e.g. HMP commands) must satisfy
this precondition, too.
In fact, any code passing around QAPI-style has_FOO, FOO pairs should
stick to the "when has_FOO is false, FOO is zero bits" convention to
keep things consistent and predictable.
> 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.
We don't -Wunused-variable, so no need to mark anything.
> 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.
Matter of taste, up to you. I just wanted to make sure you know.
>> >
>> > 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.
Okay. What about this:
# @flat: Omit nested data about the backing image, i.e. `BlockInfo`
# member 'inserted.image.backing-image' will be absent. Default is
# false. (Since 11.0)
On Wed, Feb 04, 2026 at 07:11:44 +0100, Markus Armbruster wrote:
> Peter Krempa <pkrempa@redhat.com> writes:
>
> > On Tue, Feb 03, 2026 at 13:01:01 +0100, Markus Armbruster wrote:
> >> Peter Krempa <pkrempa@redhat.com> writes:
> >>
> >> > 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>
> >>
> >> [...]
> >>
> >> > 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.
>
> Verbose version: This is a QMP command handler. The generated
> unmarshaler passes has_flat=false, flat=false when @flat is absent, and
> has_flat=true, flat=F when @flat is present with value F. Therefore,
> flat can only be true when has_flat is also true. Therefore, flat
> implies has_flat.
>
> Other code calling QMP command handlers (e.g. HMP commands) must satisfy
> this precondition, too.
>
> In fact, any code passing around QAPI-style has_FOO, FOO pairs should
> stick to the "when has_FOO is false, FOO is zero bits" convention to
> keep things consistent and predictable.
That very much makes sense, thanks for the explanation.
>
> > 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.
>
> We don't -Wunused-variable, so no need to mark anything.
Aaah! I'm too used to libvirt where we do use that warning. In such case
this (obviously without marking 'has_flat' as unused) is the simplest
then.
> > 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.
>
> Matter of taste, up to you. I just wanted to make sure you know.
>
> >> >
> >> > 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.
>
> Okay. What about this:
>
> # @flat: Omit nested data about the backing image, i.e. `BlockInfo`
> # member 'inserted.image.backing-image' will be absent. Default is
> # false. (Since 11.0)
I had to re-wrap this slightly as sphinx moaned about > 70 column line
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