[PATCH 02/19] vircgroup: introduce virCgroupV2DevicesAvailable

[Pavel Hrdina <phrdina@xxxxxxxxxx>]

There is no exact way how to figure out whether BPF devices support is
compiled into kernel.  One way is to check kernel configure options but
this is not reliable as it may not be available.  Let's try to do
syscall to which will list BPF cgroup device programs.

Signed-off-by: Pavel Hrdina <phrdina@xxxxxxxxxx>
---
 src/Makefile.am        |  1 +
 src/util/vircgroupv2.c | 37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/Makefile.am b/src/Makefile.am
index e2b89e27e8..3de926403f 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -670,6 +670,7 @@ libvirt_setuid_rpc_client_la_SOURCES = \
 		util/viratomic.c \
 		util/viratomic.h \
 		util/virbitmap.c \
+		util/virbpf.c \
 		util/virbuffer.c \
 		util/vircgroup.c \
 		util/vircgroupbackend.c \
diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
index cd58491da1..0adc0d4d23 100644
--- a/src/util/vircgroupv2.c
+++ b/src/util/vircgroupv2.c
@@ -20,8 +20,13 @@
 #include <config.h>
 
 #ifdef __linux__
+# include <fcntl.h>
+# include <linux/bpf.h>
 # include <mntent.h>
 # include <sys/mount.h>
+# include <sys/stat.h>
+# include <sys/syscall.h>
+# include <sys/types.h>
 #endif /* __linux__ */
 
 #include "internal.h"
@@ -29,6 +34,7 @@
 #define LIBVIRT_VIRCGROUPPRIV_H_ALLOW
 #include "vircgrouppriv.h"
 
+#include "virbpf.h"
 #include "vircgroup.h"
 #include "vircgroupbackend.h"
 #include "vircgroupv2.h"
@@ -280,6 +286,31 @@ virCgroupV2ParseControllersFile(virCgroupPtr group)
 }
 
 
+static bool
+virCgroupV2DevicesAvailable(virCgroupPtr group)
+{
+    bool ret = false;
+    int cgroupfd = -1;
+    unsigned int progCnt = 0;
+
+    cgroupfd = open(group->unified.mountPoint, O_RDONLY);
+    if (cgroupfd < 0) {
+        VIR_DEBUG("failed to open cgroup '%s'", group->unified.mountPoint);
+        goto cleanup;
+    }
+
+    if (virBPFQueryProg(cgroupfd, 0, BPF_CGROUP_DEVICE, &progCnt, NULL) < 0) {
+        VIR_DEBUG("failed to query cgroup progs");
+        goto cleanup;
+    }
+
+    ret = true;
+ cleanup:
+    VIR_FORCE_CLOSE(cgroupfd);
+    return ret;
+}
+
+
 static int
 virCgroupV2DetectControllers(virCgroupPtr group,
                              int controllers)
@@ -292,6 +323,8 @@ virCgroupV2DetectControllers(virCgroupPtr group,
     /* 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;
+    if (virCgroupV2DevicesAvailable(group))
+        group->unified.controllers |= 1 << VIR_CGROUP_CONTROLLER_DEVICES;
 
     for (i = 0; i < VIR_CGROUP_CONTROLLER_LAST; i++)
         VIR_DEBUG("Controller '%s' present=%s",
@@ -406,8 +439,10 @@ virCgroupV2MakeGroup(virCgroupPtr parent ATTRIBUTE_UNUSED,
                     continue;
 
                 /* Controllers that are implicitly enabled if available. */
-                if (i == VIR_CGROUP_CONTROLLER_CPUACCT)
+                if (i == VIR_CGROUP_CONTROLLER_CPUACCT ||
+                    i == VIR_CGROUP_CONTROLLER_DEVICES) {
                     continue;
+                }
 
                 if (virCgroupV2EnableController(parent, i) < 0)
                     return -1;
-- 
2.20.1

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