On 3/2/2018 6:59 PM, Markus Armbruster wrote:
Eric Blake <ebl...@redhat.com> writes:
On 01/19/2018 06:50 AM, Anton Nefedov wrote:
+
+##
+# @BlockDriverStats:
+#
+# Statistics of a block driver (driver-specific)
+#
+# Since: 2.12
+##
+{ 'union': 'BlockDriverStats',
+ 'data': {
+ 'file': 'BlockDriverStatsFile'
+ } }
Markus has been adamant that we add no new "simple unions" (unions with
a 'discriminator' field) - because they are anything but simple in the
long run.
Indeed. You could make this a flat union, similar to BlockdevOptions:
{ 'union': 'BlockDriverStats':
'base': { 'driver': 'BlockdevDriver' },
'discriminator': 'driver',
'data': {
'file': 'BlockDriverStatsFile',
... } }
However:
+
+##
# @BlockStats:
#
# Statistics of a virtual block device or a block backing device.
@@ -785,6 +819,8 @@
#
# @stats: A @BlockDeviceStats for the device.
#
+# @driver-stats: Optional driver-specific statistics. (Since 2.12)
+#
# @parent: This describes the file block device if it has one.
# Contains recursively the statistics of the underlying
# protocol (e.g. the host file for a qcow2 image). If there is
@@ -798,6 +834,7 @@
{ 'struct': 'BlockStats',
'data': {'*device': 'str', '*node-name': 'str',
'stats': 'BlockDeviceStats',
+ '*driver-stats': 'BlockDriverStats',
You're adding a union of driver-specific stats to a struct of generic
stats. That's unnecessarily complicated. Instead, turn the struct of
generic stats into a flat union, like this:
{ 'union': 'BlockStats',
'base': { ... the generic stats, i.e. the members of BlockStats
before this patch ...
'driver': 'BlockdevDriver' }
'discriminator': 'driver',
'data': {
'file': 'BlockDriverStatsFile',
... } }
...[1] You are using it alongside a struct that already uses '-'
(node-name), so you should use dashes.
So, the difference between your proposal (a simple union) and using a
"flat union", on the wire, is yours:
"return": { ..., "driver-stats": { "type": "file", "data": {
"discard_nb_ok: ... } } }
vs. a flat union:
"return": { ..., "driver-stats": { "driver": "file", "discard-nb-ok":
... } }
where you can benefit from less nesting and a saner discriminator name.
My proposal peels off yet another level of nesting.
The output is better indeed, thanks; a little drawback is now we need to
pass the whole BlockStats to the driver so it fills its stats.
e.g. the interface:
void (*bdrv_get_stats)(BlockDriverState *bs, BlockStats *stats);
And that BlockdevDriver subset type (or a generator patch) still seems
to be needed
{ 'enum' : 'BlockdevDriverWithStats',
'data' : [ 'file' ] }