vircgroup: introduce virCgroupV2DetectControllers

Cgroup v2 has only single mount point for all controllers.  The list
of controllers is stored in cgroup.controllers file, name of controllers
are separated by space.

In cgroup v2 there is no cpuacct controller, the cpu.stat file always
exists with usage stats.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>

src/util/vircgroupv2.c

@@ -32,6 +32,7 @@
 #include "vircgroup.h"
 #include "vircgroupbackend.h"
 #include "vircgroupv2.h"
+#include "virerror.h"
 #include "virfile.h"
 #include "virlog.h"
 #include "virstring.h"
@@ -230,6 +231,73 @@ virCgroupV2StealPlacement(virCgroupPtr group)
 }
 
 
+static int
+virCgroupV2ParseControllersFile(virCgroupPtr group)
+{
+    int rc;
+    VIR_AUTOFREE(char *) contStr = NULL;
+    VIR_AUTOFREE(char *) contFile = NULL;
+    char **contList = NULL;
+    char **tmp;
+
+    if (virAsprintf(&contFile, "%s/cgroup.controllers",
+                    group->unified.mountPoint) < 0)
+        return -1;
+
+    rc = virFileReadAll(contFile, 1024 * 1024, &contStr);
+    if (rc < 0) {
+        virReportSystemError(errno, _("Unable to read from '%s'"), contFile);
+        return -1;
+    }
+
+    virTrimSpaces(contStr, NULL);
+
+    contList = virStringSplit(contStr, " ", 20);
+    if (!contList)
+        return -1;
+
+    tmp = contList;
+
+    while (*tmp) {
+        int type = virCgroupV2ControllerTypeFromString(*tmp);
+
+        if (type >= 0)
+            group->unified.controllers |= 1 << type;
+
+        tmp++;
+    }
+
+    virStringListFree(contList);
+
+    return 0;
+}
+
+
+static int
+virCgroupV2DetectControllers(virCgroupPtr group,
+                             int controllers)
+{
+    size_t i;
+
+    if (virCgroupV2ParseControllersFile(group) < 0)
+        return -1;
+
+    /* In cgroup v2 there is no cpuacct controller, the cpu.stat file always
+     * exists with usage stats. */
+    group->unified.controllers |= 1 << VIR_CGROUP_CONTROLLER_CPUACCT;
+
+    for (i = 0; i < VIR_CGROUP_CONTROLLER_LAST; i++)
+        VIR_DEBUG("Controller '%s' present=%s",
+                  virCgroupV2ControllerTypeToString(i),
+                  (group->unified.controllers & 1 << i) ? "yes" : "no");
+
+    if (controllers >= 0)
+        return controllers & group->unified.controllers;
+    else
+        return group->unified.controllers;
+}
+
+
 virCgroupBackend virCgroupV2Backend = {
     .type = VIR_CGROUP_BACKEND_TYPE_V2,
 
@@ -241,6 +309,7 @@ virCgroupBackend virCgroupV2Backend = {
     .detectPlacement = virCgroupV2DetectPlacement,
     .validatePlacement = virCgroupV2ValidatePlacement,
     .stealPlacement = virCgroupV2StealPlacement,
+    .detectControllers = virCgroupV2DetectControllers,
 };