On 10/02/2018 10:43 AM, 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@xxxxxxxxxx>
> ---
> src/util/vircgroupv2.c | 52 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)
>
> diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
> index 23bf81dae2..78497bd31d 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 +47,54 @@ VIR_ENUM_IMPL(virCgroupV2Controller, VIR_CGROUP_CONTROLLER_LAST,
>
> #ifdef __linux__
>
> +/* We're looking for one 'cgroup2' fs mount which has some
> + * controllers enabled. */
> +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) {
> + if (STREQ(entry.mnt_type, "cgroup2")) {
> + ret = true;
> + break;
> + }
> + }
> +
> + /* Systemd uses cgroup v2 for process tracking but no controller is
> + * available. We should consider this configuration as cgroup v2 is
> + * not available. */
> + if (ret) {
> + int rc;
> + VIR_AUTOFREE(char *) contFile = NULL;
> + VIR_AUTOFREE(char *) contStr = NULL;
> +
> + if (virAsprintf(&contFile, "%s/cgroup.controllers", entry.mnt_dir) < 0)
> + return false;
> +
> + rc = virFileReadAll(contFile, 1024 * 1024, &contStr);
> + if (rc < 0)
> + return false;
> +
> + if (STREQ(contStr, ""))
> + return false;
> + }
> +
> + VIR_FORCE_FCLOSE(mounts);
> + return ret;
This is wrong on two levels. Firstly, if any of those conditions under
'if (ret)' fail, then @mounts is leaked. Secondly, @ret is set but then
it's ignored and false is returned regardless.
Michal
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