nspawn: introduce the new /machine/ tree in the cgroup tree and move containers there

Containers will now carry a label (normally derived from the root
directory name, but configurable by the user), and the container's root
cgroup is /machine/<label>. This label is called "machine name", and can
cover both containers and VMs (as soon as libvirt also makes use of
/machine/).

libsystemd-login can be used to query the machine name from a process.

This patch also includes numerous clean-ups for the cgroup code.

2 files changed, 37 insertions, 6 deletions

diff --git a/man/sd_pid_get_session.xml b/man/sd_pid_get_session.xml
index d2b64195a6..543a5c0c72 100644
--- a/man/sd_pid_get_session.xml
+++ b/man/sd_pid_get_session.xml
@@ -47,7 +47,8 @@
                 <refname>sd_pid_get_unit</refname>
                 <refname>sd_pid_get_user_unit</refname>
                 <refname>sd_pid_get_owner_uid</refname>
-                <refpurpose>Determine session, service or owner of a session of a specific PID</refpurpose>
+                <refname>sd_pid_get_machine_name</refname>
+                <refpurpose>Determine session, service, owner of a session or container/VM of a specific PID</refpurpose>
         </refnamediv>
 
         <refsynopsisdiv>
@@ -77,6 +78,12 @@
                                 <paramdef>pid_t <parameter>pid</parameter></paramdef>
                                 <paramdef>uid_t* <parameter>uid</parameter></paramdef>
                         </funcprototype>
+
+                        <funcprototype>
+                                <funcdef>int <function>sd_pid_get_machine_name</function></funcdef>
+                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
+                                <paramdef>char** <parameter>name</parameter></paramdef>
+                        </funcprototype>
                 </funcsynopsis>
         </refsynopsisdiv>
 
@@ -108,7 +115,7 @@
                 function will fail. (More specifically: this call will
                 not work for processes that are part of user units,
                 use <function>sd_pid_get_user_unit()</function> for
-                that.)  The returned string needs to be freed with the
+                that.) The returned string needs to be freed with the
                 libc
                 <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                 call after use.</para>
@@ -131,6 +138,14 @@
                 and not being a shared process of a user this function
                 will fail.</para>
 
+                <para><function>sd_pid_machine_name()</function> may
+                be used to determine the name of the VM or container
+                is a member of. The machine name is a short string,
+                suitable for usage in file system paths. The returned
+                string needs to be freed with the libc
+                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                call after use.</para>
+
                 <para>If the <literal>pid</literal> parameter of any
                 of these functions is passed as 0 the operation is
                 executed for the calling process.</para>
@@ -149,10 +164,11 @@
 
                 <para>The <function>sd_pid_get_session()</function>,
                 <function>sd_pid_get_unit()</function>,
-                <function>sd_pid_get_user_unit()</function>, and
-                <function>sd_pid_get_owner_uid()</function> interfaces
-                are available as shared library, which can be compiled
-                and linked to with the
+                <function>sd_pid_get_user_unit()</function>,
+                <function>sd_pid_get_owner_uid()</function> and
+                <function>sd_pid_get_machine_name()</function>
+                interfaces are available as shared library, which can
+                be compiled and linked to with the
                 <literal>libsystemd-login</literal>
                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                 file.</para>
diff --git a/man/systemd-nspawn.xml b/man/systemd-nspawn.xml
index 8adcd946b0..4d60acb3ee 100644
--- a/man/systemd-nspawn.xml
+++ b/man/systemd-nspawn.xml
@@ -203,6 +203,21 @@
                         </varlistentry>
 
                         <varlistentry>
+                                <term><option>-M</option></term>
+                                <term><option>--machine=</option></term>
+
+                                <listitem><para>Sets the machine name
+                                for this container. This name may be
+                                used to identify this container on the
+                                host, and is used to initialize the
+                                container's hostname (which the
+                                container can choose to override,
+                                however). If not specified the last
+                                component of the root directory of the
+                                container is used.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
                                 <term><option>--uuid=</option></term>
 
                                 <listitem><para>Set the specified uuid