[libvirt PATCH 2/2] vircgroupv2devices: refactor virCgroupV2DevicesRemoveProg

[Pavel Hrdina]

When running on systemd host the cgroup itself is removed by machined
so when we reach this code the directory no longer exist. If libvirtd
was running the whole time between starting and destroying VM the
detection is skipped because we still have both FD in memory. But if
libvirtd was restarted and no operation requiring cgroup devices
executed the FDs would be 0 and libvirt would try to detect them using
the cgroup directory. This results in reporting following errors:

    libvirtd[955]: unable to open '/sys/fs/cgroup/machine.slice/machine-qemu\x2d1\x2dguest.scope/': No such file or directory
    libvirtd[955]: Failed to remove cgroup for guest

When running on non-systemd host where we handle cgroups manually this
would not happen.

When destroying VM it is not necessary to detect the BPF prog and map
because the following code only closes the FDs without doing anything
else. We could run code that would try to detach the BPF prog from the
cgroup but that is not necessary as well. If the cgroup is removed and
there is no other FD open to the prog kernel will cleanup the prog and
map eventually.

Reported-by: Eric Farman <farman at linux.ibm.com>
Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
---
 src/libvirt_private.syms      |  2 +-
 src/util/vircgroupv2.c        |  2 +-
 src/util/vircgroupv2devices.c | 14 ++++----------
 src/util/vircgroupv2devices.h |  2 +-
 4 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 119768496b..0ccde7e1b4 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1963,12 +1963,12 @@ virCgroupV2Register;
 
 # util/vircgroupv2devices.h
 virCgroupV2DevicesAvailable;
+virCgroupV2DevicesCloseProg;
 virCgroupV2DevicesCreateProg;
 virCgroupV2DevicesDetectProg;
 virCgroupV2DevicesGetKey;
 virCgroupV2DevicesGetPerms;
 virCgroupV2DevicesPrepareProg;
-virCgroupV2DevicesRemoveProg;
 
 # util/vircommand.h
 virCommandAbort;
diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
index 4664492c34..5bf087b39b 100644
--- a/src/util/vircgroupv2.c
+++ b/src/util/vircgroupv2.c
@@ -535,7 +535,7 @@ virCgroupV2Remove(virCgroupPtr group)
     if (virCgroupV2PathOfController(group, controller, "", &grppath) < 0)
         return 0;
 
-    if (virCgroupV2DevicesRemoveProg(parent) < 0)
+    if (virCgroupV2DevicesCloseProg(parent) < 0)
         return -1;
 
     return virCgroupRemoveRecursively(grppath);
diff --git a/src/util/vircgroupv2devices.c b/src/util/vircgroupv2devices.c
index 4bcc1d52fe..98ab6e8f5a 100644
--- a/src/util/vircgroupv2devices.c
+++ b/src/util/vircgroupv2devices.c
@@ -548,18 +548,12 @@ virCgroupV2DevicesPrepareProg(virCgroupPtr group)
 
 
 int
-virCgroupV2DevicesRemoveProg(virCgroupPtr group)
+virCgroupV2DevicesCloseProg(virCgroupPtr group)
 {
-    if (virCgroupV2DevicesDetectProg(group) < 0)
-        return -1;
-
-    if (group->unified.devices.progfd <= 0 && group->unified.devices.mapfd <= 0)
-        return 0;
-
-    if (group->unified.devices.mapfd >= 0)
+    if (group->unified.devices.mapfd > 0)
         VIR_FORCE_CLOSE(group->unified.devices.mapfd);
 
-    if (group->unified.devices.progfd >= 0)
+    if (group->unified.devices.progfd > 0)
         VIR_FORCE_CLOSE(group->unified.devices.progfd);
 
     return 0;
@@ -629,7 +623,7 @@ virCgroupV2DevicesPrepareProg(virCgroupPtr group G_GNUC_UNUSED)
 
 
 int
-virCgroupV2DevicesRemoveProg(virCgroupPtr group G_GNUC_UNUSED)
+virCgroupV2DevicesCloseProg(virCgroupPtr group G_GNUC_UNUSED)
 {
     return 0;
 }
diff --git a/src/util/vircgroupv2devices.h b/src/util/vircgroupv2devices.h
index 9d91256120..17ab07afa0 100644
--- a/src/util/vircgroupv2devices.h
+++ b/src/util/vircgroupv2devices.h
@@ -38,7 +38,7 @@ int
 virCgroupV2DevicesPrepareProg(virCgroupPtr group);
 
 int
-virCgroupV2DevicesRemoveProg(virCgroupPtr group);
+virCgroupV2DevicesCloseProg(virCgroupPtr group);
 
 uint32_t
 virCgroupV2DevicesGetPerms(int perms,
-- 
2.30.2