[CRIU] Missing Container Subdir in Cgroups

[Pavel Emelyanov]

On 06/21/2014 04:21 AM, Saied Kazemi wrote:
> CRIU fails to restore a process running inside a Docker container with the error message:
> 
> (00.035110)      1: Error (cgroup.c:278): cg: Can't move into blkio//docker/2fda692b0fd31c20197b84b8ca5e172679dfaf9028c7322b7bb43acf061626cf/tasks (-1/-1)
> 
> This is because the container subdirectory (i.e., 64-character ID above) is not created under docker.
> 
> I applied the following quick patch as a workaround and was able to successfully restore and resume a process
> running inside a Docker container.  But the issue requires more study and changes as simply recreating the 
> directories on demand may not be enough.

Yes, the problem with cgroup FS tree is a bit deeper. Not only we should create the
directories of cgroups tasks live in, but also create the sub-directories with no tasks
e.g. to handle the case when a task does

mkdir "cg/subcg"
echo $pid > "cg/subcg/tasks"

and we dump this app in between these two calls.

Other than this we probably should take care of the configuration of these subcgroups,
e.g. mem.* files in memsg and other stuff.

And the third thing -- there may be cgroup FS mountpoints inside the mount namespace
we dump. These should be dumped as well.


> diff --git a/cgroup.c b/cgroup.c
> index 60b560c..538cf17 100644
> --- a/cgroup.c
> +++ b/cgroup.c
> @@ -368,13 +368,15 @@ static int prepare_cgroup_sfd(CgSetEntry *root_set)
>         for (i = 0; i < root_set->n_ctls; i++) {
>                 ControllerEntry *ce = root_set->ctls[i];
>                 char *opt = ce->name;
> +               char *cp;
> +               int poff = off;
>  
>                 if (strstartswith(ce->name, "name=")) {
> -                       sprintf(paux + off, "/%s", ce->name + 5);
> +                       poff += sprintf(paux + off, "/%s", ce->name + 5);
>                         sprintf(aux, "none,%s", ce->name);
>                         opt = aux;
>                 } else
> -                       sprintf(paux + off, "/%s", ce->name);
> +                       poff += sprintf(paux + off, "/%s", ce->name);
>  
>                 if (mkdir(paux, 0700)) {
>                         pr_perror("Can't make cgyard subdir");
> @@ -385,6 +387,28 @@ static int prepare_cgroup_sfd(CgSetEntry *root_set)
>                         pr_perror("Can't mount %s cgyard", ce->name);
>                         goto err;
>                 }
> +
> +               continue;
> +
> +               if ((cp = ce->path) == NULL)
> +                       continue;
> +
> +               while (*cp) {
> +                       while (*cp && *cp == '/') {
> +                               cp++;
> +                               continue;
> +                       }
> +                       paux[poff] = '/';
> +                       while (*cp && *cp != '/') {
> +                               paux[++poff] = *cp++;
> +                               continue;
> +                       }
> +                       if (paux[poff] != '/') {
> +                               paux[++poff] = '\0';
> +                               if (mkdir(paux, 0700) == 0)
> +                                       pr_info("Created directory %s\n", paux);
> +                       }
> +               }
>         }
>  
>         pr_debug("Opening %s as cg yard\n", cg_yard);
> 
> Please let me know what you think.
> 
> --Saied
>