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

[Michal Privoznik]

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.

>          }
>      }
>  
> @@ -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