[CRIU] [PATCH v3 1/2] restore: don't pass cgroup nsroot= option to mount()

[Pavel Emelyanov]

On 03/29/2016 04:51 PM, Tycho Andersen wrote:
> On Tue, Mar 29, 2016 at 01:11:03PM +0300, Pavel Emelyanov wrote:
>> On 03/28/2016 05:46 PM, Tycho Andersen wrote:
>>> https://lkml.org/lkml/2016/3/21/777 introduces a new cgroup mount option
>>> called nsroot, but doesn't allow you to pass it to mount() to actually
>>> mount it. Let's chop this option off so that we don't get errors from
>>> mount().
>>>
>>> There may be better places to chop this off (e.g. perhaps on dump),
>>> although I think it is useful to have it in there for debugging purposes,
>>> and only costs us a few extra bytes to keep it in the images since we're
>>> going to have other cgroup options anyways.
>>>
>>> v2: handle the case where nsroot= is not the last mount option
>>>
>>> Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
>>> ---
>>>  criu/mount.c | 20 ++++++++++++++++++++
>>>  1 file changed, 20 insertions(+)
>>>
>>> diff --git a/criu/mount.c b/criu/mount.c
>>> index a425828..eb8d058 100644
>>> --- a/criu/mount.c
>>> +++ b/criu/mount.c
>>> @@ -2866,6 +2866,26 @@ static int collect_mnt_from_image(struct mount_info **pms, struct ns_id *nsid)
>>>  		/* FIXME: abort unsupported early */
>>>  		pm->fstype = decode_fstype(me->fstype, me->fsname);
>>>  
>>> +		if (pm->fstype->code == FSTYPE__CGROUP) {
>>> +			char *start;
>>> +
>>> +			start = strstr(pm->options, "nsroot=");
>>> +			if (start) {
>>> +				char *next = strchr(start, ',');
>>> +
>>> +				if (next) {
>>> +					/* skip the `,' but include the terminating \0 */
>>> +					memmove(start, next+1, strlen(next+1)+1);
>>> +				} else {
>>> +					if (start > pm->options && *(start-1) == ',')
>>> +						start--;
>>> +					*start = 0;
>>> +				}
>>> +
>>> +				pr_info("trimmed nsroot option from cgroup mount, opts now: %s\n", pm->options);
>>> +			}
>>> +		}
>>> +
>>
>> OK, so we need to keep options intact to make all the comparing machinery
>> work. That's clear.
>>
>> But I still want to keep fs-specific code out of the generic one. In the
>> fstype we have the ->mount callback that gets called when the mi is about
>> to be mounted. Would defining this callback for cgroups like this
>>
>> static int cgroup_mount(struct mount_info *mi, ...)
>> {
>> 	char *options = mi->options;
>>
>> 	cut_nsroot_opt(options);
>>
>> 	return do_simple_mount(mi, ...);
>> }
>>
>> (we have the do_simple_mount() call that just calls mount syscall) work?
> 
> Actually after talking with Serge last night, I think the most
> sensible thing might be to allow this mount option, as long as the
> passed in nsroot matches the currently existing one (which would be
> the case in CRIU). I'll reply to the kernel thread about that, but
> basically then we could drop this patch and only take patch #2.

OK, patch #2 applied then :)