[libvirt] [PATCH] Fix starting domains when kernel has no cgroups support

[Jim Fehlig]

Daniel P. Berrange wrote:
> On Fri, May 10, 2013 at 12:40:40PM -0600, Jim Fehlig wrote:
>   
>> Found that I was unable to start existing domains after updating
>> to a kernel with no cgroups support
>>
>>   # zgrep CGROUP /proc/config.gz
>>   # CONFIG_CGROUPS is not set
>>   # virsh start test
>>   error: Failed to start domain test
>>   error: Unable to initialize /machine cgroup: Cannot allocate memory
>>
>> virCgroupPartitionNeedsEscaping() correctly returns errno (ENOENT) when
>> attempting to open /proc/cgroups on such a system, but it was being
>> dropped in virCgroupSetPartitionSuffix().
>>
>> Change virCgroupSetPartitionSuffix() to propogate errors returned by
>> its callees.  Also check for ENOENT in qemuInitCgroup() when determining
>> if cgroups support is available.
>> ---
>>  src/qemu/qemu_cgroup.c |  3 ++-
>>  src/util/vircgroup.c   | 19 +++++++++++++------
>>  2 files changed, 15 insertions(+), 7 deletions(-)
>>
>> diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c
>> index 9c45b76..40777aa 100644
>> --- a/src/qemu/qemu_cgroup.c
>> +++ b/src/qemu/qemu_cgroup.c
>> @@ -414,7 +414,8 @@ int qemuInitCgroup(virQEMUDriverPtr driver,
>>          if (rc != 0) {
>>              if (rc == -ENXIO ||
>>                  rc == -EPERM ||
>> -                rc == -EACCES) { /* No cgroups mounts == success */
>> +                rc == -EACCES ||
>> +                rc == -ENOENT) { /* No cgroups mounts == success */
>>                  VIR_DEBUG("No cgroups present/configured/accessible, ignoring error");
>>                  goto done;
>>              }
>> diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
>> index 473d2fc..ef619dc 100644
>> --- a/src/util/vircgroup.c
>> +++ b/src/util/vircgroup.c
>> @@ -1167,14 +1167,14 @@ static int virCgroupPartitionEscape(char **path)
>>      return 0;
>>  }
>>  
>> -static char *virCgroupSetPartitionSuffix(const char *path)
>> +static int virCgroupSetPartitionSuffix(const char *path, char **res)
>>     
>
> You're changing the signature, but I don't see you changing any
> callers to adapt.
>   

Opps, that wouldn't even compile :).  I created/tested this patch on a
test machine and somehow dropped a hunk when merging on my dev machine. 
Unfortunately, I also didn't run my pre-patch-submit-tests on my dev
setup, totally missing this.

Here's the updated patch.

Regards,
Jim

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