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

[Michal Privoznik]

On 10/05/2018 03:48 PM, Pavel Hrdina wrote:
> On Fri, Oct 05, 2018 at 03:43:50PM +0200, Michal Privoznik wrote:
>> 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;
>> }
> 
> Works for me :) I was considering moving it inside the while loop but
> I was too lazy to do it.

ACK then. Although it feels a bit weird to ACK my own code O:-)

Michal