Revert "cgroup: do not create a sub-cgroup by default"

This reverts commit 262d6ac.

This is a breaking change, we need a version bump.

Signed-off-by: Giuseppe Scrivano <[email protected]>

Author: giuseppe

crun.1

@@ -577,28 +577,26 @@ chown -R the_user.the_user /sys/fs/cgroup/systemd
 .EE
 
 .SH \fBrun.oci.systemd.subgroup=SUBGROUP\fR
-This configuration option allows you to define a sub-cgroup that will
-be created under a systemd-managed cgroup for your container.
-
-.PP
-When SUBGROUP is specified, the complete cgroup path will follow this
-structure:
+Override the name for the systemd sub cgroup created under the systemd
+scope, so the final cgroup will be like:
 
 .EX
 /sys/fs/cgroup/$PATH/$SUBGROUP
 .EE
 
 .PP
-If \fBSUBGROUP\fR is set to \fBcontainer\fR, a typical path could be:
+When it is set to the empty string, a sub cgroup is not created.
 
-.EX
-/sys/fs/cgroup/system.slice/foo-352700.scope/container
-.EE
+.PP
+If not specified, it defaults to \fBcontainer\fR on cgroup v2, and to \fB""\fR
+on cgroup v1.
 
 .PP
-If \fBSUBGROUP\fR is set to an empty string, no sub-cgroup will be
-created.  By default, this option is not configured, meaning no
-sub-cgroup is created unless explicitly set.
+e.g.
+
+.EX
+/sys/fs/cgroup//system.slice/foo-352700.scope/container
+.EE
 
 .SH \fBrun.oci.delegate-cgroup=DELEGATED-CGROUP\fR
 If the \fBrun.oci.systemd.subgroup\fR annotation is specified, yet another

crun.1.md

@@ -489,25 +489,24 @@ chown -R the_user.the_user /sys/fs/cgroup/systemd
 
 ## `run.oci.systemd.subgroup=SUBGROUP`
 
-This configuration option allows you to define a sub-cgroup that will
-be created under a systemd-managed cgroup for your container.
-
-When SUBGROUP is specified, the complete cgroup path will follow this
-structure:
+Override the name for the systemd sub cgroup created under the systemd
+scope, so the final cgroup will be like:
 
 ```
 /sys/fs/cgroup/$PATH/$SUBGROUP
 ```
 
-If `SUBGROUP` is set to `container`, a typical path could be:
+When it is set to the empty string, a sub cgroup is not created.
+
+If not specified, it defaults to `container` on cgroup v2, and to `""`
+on cgroup v1.
+
+e.g.
+
 ```
-/sys/fs/cgroup/system.slice/foo-352700.scope/container
+/sys/fs/cgroup//system.slice/foo-352700.scope/container
 ```
 
-If `SUBGROUP` is set to an empty string, no sub-cgroup will be
-created.  By default, this option is not configured, meaning no
-sub-cgroup is created unless explicitly set.
-
 ## `run.oci.delegate-cgroup=DELEGATED-CGROUP`
 
 If the `run.oci.systemd.subgroup` annotation is specified, yet another

src/libcrun/cgroup-systemd.c

@@ -1987,7 +1987,7 @@ find_systemd_subgroup (string_map *annotations)
       return annotation;
     }
 
-  return NULL;
+  return "container";
 }
 
 static int