[Devel] [PATCH RHEL8 COMMIT] ve/cgroup: Add helper function to get ve-related cgroup paths

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.5
------>
commit 9228c167b67db7819c5de6b298b16330b1f98178
Author: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
Date:   Wed Mar 3 20:21:12 2021 +0300

    ve/cgroup: Add helper function to get ve-related cgroup paths
    
    This fill make fake-absolute paths to support virtual ve roots in
    cgroup hierarchies.
    The path will be used in subsequent patches.
    
    Signed-off-by: Valeriy.Vdovin <valeriy.vdovin at virtuozzo.com>
    Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    =====================
    Patchset description:
    
    ve/cgroup: Port release_agent virtualization from vz7
    
    This patchset ports virtualization of cgroup release_agent
    virtualization from vz7.
    
    Major challanges of porting are differences between vz7 and vz8 cgroup
    implementations:
    - transition of cgroups to kernfs
    - slightly changed locking scheme, which relies on css_set_lock in
      places, previously relied on cgroup_mutex.
    
    There is a small number of patches that have been ported without
    modifications, but most of the patches had suffered a lot of
    modification due to the factors described above.
    
    v1:
      - original patchset
    v2:
      - removed port of CGRP_REMOVED due to the use of CSS_ONLINE in VZ8 for
        same reason
      - changed ve_set(get)_release_agent_path signature for more optimal
      - added ve->is_running check before calling userspace executable
    v3:
      - use goto after check for ve->is_running in last patch
---
 kernel/cgroup/cgroup-v1.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index fb06fc9d96ca..21a7c36fbf44 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -787,6 +787,16 @@ void cgroup1_check_for_release(struct cgroup *cgrp)
 		schedule_work(&cgrp->release_agent_work);
 }
 
+/*
+ * Used to get a fake-absolute path to a cgroup on kernfs filesystem, but it
+ * actually be relative to cgroup root, provided in the argument.
+ */
+static inline int cgroup_path_ve_relative(struct cgroup *ve_root_cgrp,
+	struct cgroup *cgrp, char *buf, size_t buflen)
+{
+	return kernfs_path_from_node(cgrp->kn, ve_root_cgrp->kn, buf, buflen);
+}
+
 /*
  * Notify userspace when a cgroup is released, by running the
  * configured release agent with the name of the cgroup (path