[libvirt] [PATCH 1/4] qemu: During startup need more QEMU_CAPS_OBJECT_IOTHREAD checks

[John Ferlan]

On 10/13/2015 12:08 PM, Peter Krempa wrote:
> On Tue, Oct 13, 2015 at 11:47:07 -0400, John Ferlan wrote:
>> During qemu process startup (qemuProcessStart), the call to
>> qemuProcessDetectIOThreadPIDs will not attempt to fill in the
>> ->thread_id values if the binary doesn't support IOThreads.
>> However, subsequent calls to setup the IOThread cgroups, affinity,
>> and scheduler parameters had no such check, thus could attempt
>> to set thread_id = 0, which would not be a good idea.
>>
>> Signed-off-by: John Ferlan <jferlan at redhat.com>
>> ---
>>  src/qemu/qemu_cgroup.c  |  3 +++
>>  src/qemu/qemu_process.c | 18 ++++++++++++------
>>  2 files changed, 15 insertions(+), 6 deletions(-)
> 
> Do we even allow to start a VM that has IOthreads enabled but qemu does
> not support them? In that case that's the point to fix so that we have a
> central point where it's checked.
> 

hmm...  I guess these changes were more CYA than anything else... Look
for any callers to the API's that were doing actions based on
niothreadids and make sure we add the caps check. Blind ambition.

I'll adjust this patch to be just the if (def->niothreads == 0) return
0; in qemuSetupCgroupForIOThreads

John
>>
>> diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c
>> index 570dab5..66318ea 100644
>> --- a/src/qemu/qemu_cgroup.c
>> +++ b/src/qemu/qemu_cgroup.c
>> @@ -1163,6 +1163,9 @@ qemuSetupCgroupForIOThreads(virDomainObjPtr vm)
>>      char *mem_mask = NULL;
>>      virDomainNumatuneMemMode mem_mode;
>>  
>> +    if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_OBJECT_IOTHREAD))
>> +        return 0;
> 
> Spreading checks like this through the code usually ends up to be
> fragile.
> 
> I think this should be if (def->niothreads == 0) return 0;
> 
>> +
>>      if ((period || quota) &&
>>          !virCgroupHasController(priv->cgroup, VIR_CGROUP_CONTROLLER_CPU)) {
>>          virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
>> index 8aa9efc..67e7cbc 100644
>> --- a/src/qemu/qemu_process.c
>> +++ b/src/qemu/qemu_process.c
>> @@ -2514,10 +2514,14 @@ qemuProcessSetEmulatorAffinity(virDomainObjPtr vm)
>>  static int
>>  qemuProcessSetIOThreadsAffinity(virDomainObjPtr vm)
>>  {
>> +    qemuDomainObjPrivatePtr priv = vm->privateData;
>>      virDomainDefPtr def = vm->def;
>>      size_t i;
>>      int ret = -1;
>>  
>> +    if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_OBJECT_IOTHREAD))
>> +        return 0;
>> +
>>      for (i = 0; i < def->niothreadids; i++) {
> 
> Here this function is doing the right thing.
> 
>>          /* set affinity only for existing iothreads */
>>          if (!def->iothreadids[i]->cpumask)
>> @@ -2574,12 +2578,14 @@ qemuProcessSetSchedulers(virDomainObjPtr vm)
>>              return -1;
>>      }
>>  
>> -    for (i = 0; i < vm->def->niothreadids; i++) {
>> -        if (qemuProcessSetSchedParams(vm->def->iothreadids[i]->iothread_id,
>> -                                      vm->def->iothreadids[i]->thread_id,
>> -                                      vm->def->cputune.niothreadsched,
>> -                                      vm->def->cputune.iothreadsched) < 0)
>> -            return -1;
>> +    if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_OBJECT_IOTHREAD)) {
>> +        for (i = 0; i < vm->def->niothreadids; i++) {
> 
> As well as here.
> 
>> +            if (qemuProcessSetSchedParams(vm->def->iothreadids[i]->iothread_id,
>> +                                          vm->def->iothreadids[i]->thread_id,
>> +                                          vm->def->cputune.niothreadsched,
>> +                                          vm->def->cputune.iothreadsched) < 0)
>> +                return -1;
>> +        }
> 
> Peter
>