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Re: [libvirt] [PATCH 2/6] introduce the function virCgroupMoveTask()



On Wed, Apr 25, 2012 at 05:44:52PM +0800, Wen Congyang wrote:
> introduce a new API to move all tasks from a cgroup to another cgroup
> 
> ---
>  src/util/cgroup.c |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  src/util/cgroup.h |    2 +
>  2 files changed, 57 insertions(+), 0 deletions(-)
> 
> diff --git a/src/util/cgroup.c b/src/util/cgroup.c
> index 901a841..724cc6e 100644
> --- a/src/util/cgroup.c
> +++ b/src/util/cgroup.c
> @@ -789,6 +789,61 @@ int virCgroupAddTask(virCgroupPtr group, pid_t pid)
>      return rc;
>  }
>  
> +static int virCgrouAddTaskStr(virCgroupPtr group, const char *pidstr)
> +{
> +    unsigned long long value;
> +
> +    if (virStrToLong_ull(pidstr, NULL, 10, &value) < 0)
> +        return -EINVAL;
> +
> +    return virCgroupAddTask(group, value);
> +}
> +
> +/**
> + * virCgroupMoveTask:
> + *
> + * @src_group: The source cgroup where all tasks are removed from
> + * @dest_group: The destination where all tasks are added to
> + *
> + * Returns: 0 on success
> + */
> +int virCgroupMoveTask(virCgroupPtr src_group, virCgroupPtr dest_group)
> +{
> +    int rc = 0;
> +    int i;
> +    char *content, *value, *next;
> +
> +    for (i = 0 ; i < VIR_CGROUP_CONTROLLER_LAST ; i++) {
> +        /* Skip over controllers not mounted */
> +        if (!src_group->controllers[i].mountPoint ||
> +            !dest_group->controllers[i].mountPoint)
> +            continue;
> +
> +        rc = virCgroupGetValueStr(src_group, i, "tasks", &content);
> +        if (rc != 0)
> +            break;
> +
> +        value = content;
> +        while((next = strchr(value, '\n')) != NULL) {
> +            *next = '\0';
> +            if ((rc = virCgrouAddTaskStr(dest_group, value) < 0))
> +                goto cleanup;
> +            value = next + 1;
> +        }
> +        if (*value != '\0') {
> +            if ((rc = virCgrouAddTaskStr(dest_group, value) < 0))
> +                goto cleanup;
> +        }
> +
> +        VIR_FREE(content);
> +    }
> +
> +    return 0;
> +
> +cleanup:
> +    virCgroupMoveTask(dest_group, src_group);

If we get here, the tasks that are originally in dest_group can be
mistakenly moved to src_group.

And, note that this is a recursive call, there is the possibility 
it ends up with a endless call to virCgroupMoveTask if all fail because
of the same error.

-- 
Thanks,
Hu Tao


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