[libvirt] [PATCH 42/53] vircgroup: add support for hybrid configuration

[Fabiano Fidêncio]

On Fri, 2018-10-05 at 12:14 +0200, Michal Privoznik wrote:
> On 10/02/2018 10:44 AM, Pavel Hrdina wrote:
> > This enables to use both cgroup v1 and v2 at the same time together
> > with libvirt.  It is supported by kernel and there is valid use-
> > case,
> > not all controllers are implemented in cgroup v2 so there might be
> > configurations where administrator would enable these missing
> > controllers in cgroup v1.
> > 
> > Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> > ---
> >  src/util/vircgroup.c        | 351 ++++++++++++++++++++++++++----
> > ------
> >  src/util/vircgroupbackend.c |  20 ++
> >  src/util/vircgroupbackend.h |  16 +-
> >  src/util/vircgrouppriv.h    |   2 +-
> >  4 files changed, 291 insertions(+), 98 deletions(-)
> > 
> > diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
> > index dc249bfe33..4aec5f1bcf 100644
> > --- a/src/util/vircgroup.c
> > +++ b/src/util/vircgroup.c
> > @@ -228,6 +228,7 @@ virCgroupDetectMounts(virCgroupPtr group)
> >      struct mntent entry;
> >      char buf[CGROUP_MAX_VAL];
> >      int ret = -1;
> > +    size_t i;
> >  
> >      mounts = fopen("/proc/mounts", "r");
> >      if (mounts == NULL) {
> > @@ -236,11 +237,14 @@ virCgroupDetectMounts(virCgroupPtr group)
> >      }
> >  
> >      while (getmntent_r(mounts, &entry, buf, sizeof(buf)) != NULL)
> > {
> > -        if (group->backend->detectMounts(group,
> > -                                         entry.mnt_type,
> > -                                         entry.mnt_opts,
> > -                                         entry.mnt_dir) < 0) {
> > -            goto cleanup;
> > +        for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
> > +            if (group->backends[i] &&
> > +                group->backends[i]->detectMounts(group,
> > +                                                 entry.mnt_type,
> > +                                                 entry.mnt_opts,
> > +                                                 entry.mnt_dir) <
> > 0) {
> > +                goto cleanup;
> > +            }
> >          }
> >      }
> >  
> > @@ -303,6 +307,7 @@ virCgroupDetectPlacement(virCgroupPtr group,
> >      }
> >  
> >      while (fgets(line, sizeof(line), mapping) != NULL) {
> > +        size_t i;
> >          char *controllers = strchr(line, ':');
> >          char *selfpath = controllers ? strchr(controllers + 1,
> > ':') : NULL;
> >          char *nl = selfpath ? strchr(selfpath, '\n') : NULL;
> > @@ -317,9 +322,12 @@ virCgroupDetectPlacement(virCgroupPtr group,
> >          controllers++;
> >          selfpath++;
> >  
> > -        if (group->backend->detectPlacement(group, path,
> > controllers,
> > -                                            selfpath) < 0) {
> > -            goto cleanup;
> > +        for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
> > +            if (group->backends[i] &&
> > +                group->backends[i]->detectPlacement(group, path,
> > controllers,
> > +                                                    selfpath) < 0)
> > {
> > +                goto cleanup;
> > +            }
> 
> So a loop like this appears all over the patch:
> 
> for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
>   if (group->backends[i] &&
>       group->backends[i]->cb();
> }
> 
> I wonder if we should have wrappers around these chunks of code. But
> that could be saved as a follow up patch.

We already have a macro for something similar that could be expanded
and reused in all of those.
And, yes, I totally agree that it could be done as a follow-up patch.

> 
> >          }
> >      }
> >  
> > @@ -338,8 +346,9 @@ virCgroupDetect(virCgroupPtr group,
> >                  const char *path,
> >                  virCgroupPtr parent)
> >  {
> > -    int rc;
> >      size_t i;
> > +    bool backendAvailable = false;
> > +    int controllersAvailable = 0;
> >      virCgroupBackendPtr *backends = virCgroupBackendGetAll();
> >  
> >      VIR_DEBUG("group=%p controllers=%d path=%s parent=%p",
> > @@ -350,31 +359,40 @@ virCgroupDetect(virCgroupPtr group,
> >  
> >      for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
> >          if (backends[i] && backends[i]->available()) {
> > -            group->backend = backends[i];
> > -            break;
> > +            group->backends[i] = backends[i];
> > +            backendAvailable = true;
> 
> No need to remove the 'break'.
> 
> >          }
> >      }
> 
> ACK
> 
> 
> Michal
> 
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