[CRIU] [PATCH] Skip restoring certain cgroup root directories when using full mode

[Pavel Emelyanov]

On 08/19/2015 12:40 AM, Hui Kang wrote:
> 
> 
> On Tue, Aug 18, 2015 at 11:13 AM, Pavel Emelyanov <xemul at parallels.com <mailto:xemul at parallels.com>> wrote:
> 
>     On 08/18/2015 12:55 AM, Hui Kang wrote:
>     > On Mon, Aug 17, 2015 at 10:48 AM, Pavel Emelyanov <xemul at parallels.com <mailto:xemul at parallels.com>> wrote:
>     >> On 08/17/2015 08:07 AM, Hui Kang wrote:
>     >>> On Sun, Aug 16, 2015 at 9:20 PM, Pavel Emelyanov <xemul at parallels.com <mailto:xemul at parallels.com>> wrote:
>     >>>> On 08/13/2015 07:41 PM, Hui Kang wrote:
>     >>>>> Skip these top cgroup directories: cpu, cpuset, cpuacct, memory
>     >>>>>
>     >>>>> Signed-off-by: Hui Kang <hkang.sunysb at gmail.com <mailto:hkang.sunysb at gmail.com>>
>     >>>>> ---
>     >>>>>  cgroup.c | 4 ++++
>     >>>>>  1 file changed, 4 insertions(+)
>     >>>>>
>     >>>>> diff --git a/cgroup.c b/cgroup.c
>     >>>>> index a4e0146..94749b1 100644
>     >>>>> --- a/cgroup.c
>     >>>>> +++ b/cgroup.c
>     >>>>> @@ -992,6 +992,10 @@ static int prepare_cgroup_dir_properties(char *path, int off, CgroupDirEntry **e
>     >>>>>               CgroupDirEntry *e = ents[i];
>     >>>>>               size_t off2 = off;
>     >>>>>
>     >>>>> +             if (strcmp(e->dir_name, "") == 0 &&
>     >>>>> +                 ((strstr(path, "cpu")) || (strstr(path, "memory"))))
>     >>>>> +                     continue;
>     >>>>> +
>     >>>>
>     >>>> With this "continue" won't we skip all the properties restore? The e-s we
>     >>>> have here represent all the tree, starting from root and descending. If you
>     >>>> skip the root one, then the whole subtree is skipped too.
>     >>>
>     >>> No. Although the e-s represent the tree, the for loops will iterate
>     >>> all the directories.
>     >>
>     >> The loop iterates top-level directories, then dives into children. Can you show
>     >> the contents of your cgroup.img file?
>     >
>     > {
>     >     "magic": "CGROUP",
>     >     "entries": [
> 
>     Ah, I see. The thing is that in your case you don't have nested directories. In
>     particular -- cpuset is only the "foo/foo1" dir, so your check doesn't match
>     one and it's restored. The cpu/cpuacct are both "/" only, so you check matches
>     them, skips, but we notice nothing as there are no sub-directories.
> 
> 
> HI, Pavel,
> can you give me an example which has nested directories? I added the process to foo/foo1/tasks and then dump the process. So no value in foo is dumped.
> 
> For a nested cgroup directory, do you mean I should also add a parent tasks to foo and then dump both parent and child?

Create at least two directories (foo/A and foo/A/B) and two tasks living in each. This will give you
two entries in image file.

The bug I'm thinking of would happen if you have groups / and /A and two tasks living in each (again).
With your patch the /A's props will not be restored.

-- Pavel