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[libvirt] [RFC PATCH] lxc: don't return error on GetInfo when cgroups not yet set up



Nova (openstack) calls libvirt to create a container, then
periodically checks using GetInfo to see whether the container
is up.  If it does this too quickly, then libvirt returns an
error, which in libvirt.py causes an exception to be raised,
the same type as if the container was bad.

This may not be the best way to handle it, but with this
patch, we assume that a -ENOENT return from virCgroupForDomain
means the cgroups are not yet set up, and so we return the
same values for cpu and memory usage as if the domain was not
active.

Signed-off-by: Serge Hallyn <serge hallyn canonical com>
---
 src/lxc/lxc_driver.c |   37 +++++++++++++++++++++----------------
 1 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/src/lxc/lxc_driver.c b/src/lxc/lxc_driver.c
index 4b62600..a68b8e7 100644
--- a/src/lxc/lxc_driver.c
+++ b/src/lxc/lxc_driver.c
@@ -542,26 +542,31 @@ static int lxcDomainGetInfo(virDomainPtr dom,
         info->cpuTime = 0;
         info->memory = vm->def->mem.cur_balloon;
     } else {
-        if (virCgroupForDomain(driver->cgroup, vm->def->name, &cgroup, 0) != 0) {
+        int ret = virCgroupForDomain(driver->cgroup, vm->def->name, &cgroup, 0);
+        if (ret == -ENOENT) {
+            /* cgroups are not set up yet */
+            info->cpuTime = 0;
+            info->memory = vm->def->mem.cur_balloon;
+        } else if (ret != 0) {
             lxcError(VIR_ERR_INTERNAL_ERROR,
                      _("Unable to get cgroup for %s"), vm->def->name);
             goto cleanup;
-        }
-
-        if (virCgroupGetCpuacctUsage(cgroup, &(info->cpuTime)) < 0) {
-            lxcError(VIR_ERR_OPERATION_FAILED,
-                     "%s", _("Cannot read cputime for domain"));
-            goto cleanup;
-        }
-        if ((rc = virCgroupGetMemoryUsage(cgroup, &(info->memory))) < 0) {
-            lxcError(VIR_ERR_OPERATION_FAILED,
-                     "%s", _("Cannot read memory usage for domain"));
-            if (rc == -ENOENT) {
-                /* Don't fail if we can't read memory usage due to a lack of
-                 * kernel support */
-                info->memory = 0;
-            } else
+        } else {
+            if (virCgroupGetCpuacctUsage(cgroup, &(info->cpuTime)) < 0) {
+                lxcError(VIR_ERR_OPERATION_FAILED,
+                         "%s", _("Cannot read cputime for domain"));
                 goto cleanup;
+            }
+            if ((rc = virCgroupGetMemoryUsage(cgroup, &(info->memory))) < 0) {
+                lxcError(VIR_ERR_OPERATION_FAILED,
+                         "%s", _("Cannot read memory usage for domain"));
+                if (rc == -ENOENT) {
+                    /* Don't fail if we can't read memory usage due to a lack of
+                     * kernel support */
+                    info->memory = 0;
+                } else
+                    goto cleanup;
+            }
         }
     }
 
-- 
1.7.5.4


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