allow: now allowed on shmem-adopted topologies

A shmem topology may now be shared between different cgroups, one only has
to call hwloc_topology_allow(LOCAL) to update the list of allowed CPUs and memory
after adopting the shmem topo.
The source process must have built the original topology with INCLUDE_DISALLOWED.

This was disabled previously because allow(LOCAL) is supposed to add "LinuxCgroup"
to the info attrs, which was not possible until we added topo infos in 3.0.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

Author: bgoglin

NEWS

@@ -61,6 +61,9 @@ Version 3.0.0
   + HWLOC_PCI_<domain>_<bus>_LOCALCPUS environment variables,
     superseded with a single HWLOC_PCI_LOCALITY since 2.0.
 * Misc
+  + hwloc_topology_allow() is now possible on shmem-adopted topology.
+    This allows to share a topology between processes in different
+    Linux cgroups, etc.
   + XML format switches to 3.0 by default. Exporting to 2.x is
     possible with the new V2 XML export flag.
 

hwloc/topology.c

@@ -4588,11 +4588,6 @@ hwloc_topology_allow(struct hwloc_topology *topology,
   if (!(topology->state & HWLOC_TOPOLOGY_STATE_IS_LOADED))
     goto einval;
 
-  if (topology->adopted_shmem_addr) {
-    errno = EPERM;
-    goto error;
-  }
-
   if (!(topology->flags & HWLOC_TOPOLOGY_FLAG_INCLUDE_DISALLOWED))
     goto einval;
 

include/hwloc.h

@@ -2688,6 +2688,10 @@ enum hwloc_allow_flags_e {
  *
  * \return 0 on success, -1 on error.
  *
+ * \note This function is allowed on an adopted topology (see \ref hwlocality_shmem).
+ * The flag ::HWLOC_TOPOLOGY_FLAG_INCLUDE_DISALLOWED is required on the original
+ * topology (before sharing).
+ *
  * \note Removing objects from a topology should rather be performed with
  * hwloc_topology_restrict().
  */

include/hwloc/shmem.h

@@ -98,6 +98,9 @@ HWLOC_DECLSPEC int hwloc_shmem_topology_write(hwloc_topology_t topology,
  * However the topology is read-only.
  * For instance, it cannot be modified with hwloc_topology_restrict()
  * and object userdata pointers cannot be changed.
+ * The only exception is hwloc_topology_allow() which may be used to expose
+ * a different set of allowed CPUs and memory. This requires that the original
+ * topology (before sharing) was loaded with flag ::HWLOC_TOPOLOGY_FLAG_INCLUDE_DISALLOWED.
  *
  * The segment of the file pointed by descriptor \p fd,
  * starting at offset \p fileoffset, and of length \p length (in bytes),