[libvirt] [PATCH v2 02/53] vircgroup: introduce virCgroupV2Available

[Michal Privoznik]

On 10/05/2018 02:43 PM, Pavel Hrdina wrote:
> We cannot detect only mount points to figure out whether cgroup v2
> is available because systemd uses cgroup v2 for process tracking and
> all controllers are mounted as cgroup v1 controllers.
> 
> To make sure that this is no the situation we need to check
> 'cgroup.controllers' file if it's not empty to make sure that cgroup
> v2 is not mounted only for process tracking.
> 
> Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> ---
>  src/util/vircgroupv2.c | 59 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
> 
> diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
> index 23bf81dae2..83944602d6 100644
> --- a/src/util/vircgroupv2.c
> +++ b/src/util/vircgroupv2.c
> @@ -19,6 +19,10 @@
>   */
>  #include <config.h>
>  
> +#ifdef __linux__
> +# include <mntent.h>
> +#endif /* __linux__ */
> +
>  #include "internal.h"
>  
>  #define __VIR_CGROUP_ALLOW_INCLUDE_PRIV_H__
> @@ -28,7 +32,9 @@
>  #include "vircgroup.h"
>  #include "vircgroupbackend.h"
>  #include "vircgroupv2.h"
> +#include "virfile.h"
>  #include "virlog.h"
> +#include "virstring.h"
>  
>  VIR_LOG_INIT("util.cgroup");
>  
> @@ -41,8 +47,61 @@ VIR_ENUM_IMPL(virCgroupV2Controller, VIR_CGROUP_CONTROLLER_LAST,
>  
>  #ifdef __linux__


How about:

static bool
virCgroupV2Available(void)
{
    bool ret = false;
    FILE *mounts = NULL;
    struct mntent entry;
    char buf[CGROUP_MAX_VAL];

    if (!(mounts = fopen("/proc/mounts", "r")))
        return false;

    while (getmntent_r(mounts, &entry, buf, sizeof(buf)) != NULL) {
        VIR_AUTOFREE(char *) contFile = NULL;
        VIR_AUTOFREE(char *) contStr = NULL;

        if (STRNEQ(entry.mnt_type, "cgroup2"))
            continue;

        /* Systemd uses cgroup v2 for process tracking but no controller is
         * available. We should consider this configuration as cgroup v2 is
         * not available. */
        if (virAsprintf(&contFile, "%s/cgroup.controllers", entry.mnt_dir) < 0)
            goto cleanup;

        if (virFileReadAll(contFile, 1024 * 1024, &contStr) < 0)
            goto cleanup;

        if (STREQ(contStr, ""))
            continue;

        ret = true;
        break;
    }

 cleanup:
    VIR_FORCE_FCLOSE(mounts);
    return ret;
}


Michal