hmp: add filtering of statistics by name

Allow the user to request only a specific subset of statistics.
This can be useful when working on a feature or optimization that is
known to affect that statistic.

Example:

   (qemu) info stats vcpu halt_poll_fail_ns
   provider: kvm
       halt_poll_fail_ns (cumulative, ns): 0

In case multiple providers have the same statistic, the provider can be
specified too:

   (qemu) info stats vcpu halt_poll_fail_ns kvm
   provider: kvm
       halt_poll_fail_ns (cumulative, ns): 0

Extracted from a patch by Mark Kanda.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hmp-commands-info.hx

@@ -897,10 +897,10 @@ ERST
 
     {
         .name       = "stats",
-        .args_type  = "target:s,provider:s?",
-        .params     = "target [provider]",
-        .help       = "show statistics for the given target (vm or vcpu); optionally filter by "
-                      "provider",
+        .args_type  = "target:s,names:s?,provider:s?",
+        .params     = "target [names] [provider]",
+        .help       = "show statistics for the given target (vm or vcpu); optionally filter by"
+                      "name (comma-separated list, or * for all) and provider",
         .cmd        = hmp_info_stats,
     },
 

monitor/hmp-cmds.c

@@ -2359,10 +2359,12 @@ static void print_stats_results(Monitor *mon, StatsTarget target,
 }
 
 /* Create the StatsFilter that is needed for an "info stats" invocation.  */
-static StatsFilter *stats_filter(StatsTarget target, int cpu_index,
-                                 StatsProvider provider)
+static StatsFilter *stats_filter(StatsTarget target, const char *names,
+                                 int cpu_index, StatsProvider provider)
 {
     StatsFilter *filter = g_malloc0(sizeof(*filter));
+    StatsProvider provider_idx;
+    StatsRequestList *request_list = NULL;
 
     filter->target = target;
     switch (target) {
@@ -2383,15 +2385,29 @@ static StatsFilter *stats_filter(StatsTarget target, int cpu_index,
         break;
     }
 
-    if (provider == STATS_PROVIDER__MAX) {
+    if (!names && provider == STATS_PROVIDER__MAX) {
         return filter;
     }
 
-    /* "info stats" can only query either one or all the providers.  */
+    /*
+     * "info stats" can only query either one or all the providers.  Querying
+     * by name, but not by provider, requires the creation of one filter per
+     * provider.
+     */
+    for (provider_idx = 0; provider_idx < STATS_PROVIDER__MAX; provider_idx++) {
+        if (provider == STATS_PROVIDER__MAX || provider == provider_idx) {
+            StatsRequest *request = g_new0(StatsRequest, 1);
+            request->provider = provider_idx;
+            if (names && !g_str_equal(names, "*")) {
+                request->has_names = true;
+                request->names = strList_from_comma_list(names);
+            }
+            QAPI_LIST_PREPEND(request_list, request);
+        }
+    }
+
     filter->has_providers = true;
-    filter->providers = g_new0(StatsRequestList, 1);
-    filter->providers->value = g_new0(StatsRequest, 1);
-    filter->providers->value->provider = provider;
+    filter->providers = request_list;
     return filter;
 }
 
@@ -2399,6 +2415,7 @@ void hmp_info_stats(Monitor *mon, const QDict *qdict)
 {
     const char *target_str = qdict_get_str(qdict, "target");
     const char *provider_str = qdict_get_try_str(qdict, "provider");
+    const char *names = qdict_get_try_str(qdict, "names");
 
     StatsProvider provider = STATS_PROVIDER__MAX;
     StatsTarget target;
@@ -2429,11 +2446,11 @@ void hmp_info_stats(Monitor *mon, const QDict *qdict)
 
     switch (target) {
     case STATS_TARGET_VM:
-        filter = stats_filter(target, -1, provider);
+        filter = stats_filter(target, names, -1, provider);
         break;
     case STATS_TARGET_VCPU: {}
         int cpu_index = monitor_get_cpu_index(mon);
-        filter = stats_filter(target, cpu_index, provider);
+        filter = stats_filter(target, names, cpu_index, provider);
         break;
     default:
         abort();