linux: mark HPE Cray Cassini HSNs with subtype "Slingshot"

Those are almost identical to Ethernet NICs.

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

doc/hwloc.doxy

@@ -1536,6 +1536,7 @@ components when I/O discovery is enabled and supported.
 <li>Network interfaces (::HWLOC_OBJ_OSDEV_NETWORK)
  <ul>
  <li><em>eth0</em>, <em>wlan0</em>, <em>ib0</em> (Linux component)</li>
+ <li><em>hsn0</em> with "Slingshot" subtype for HPE Cray HSNs (Linux component).</li>
  </ul>
 </li>
 <li>OpenFabrics (InfiniBand, Omni-Path, usNIC, etc) HCAs (::HWLOC_OBJ_OSDEV_OPENFABRICS)
@@ -1812,6 +1813,7 @@ subtype <tt>Cluster</tt>, <tt>Module</tt>, <tt>Tile</tt>, <tt>Compute Unit</tt>,
 <li>Co-processor: subtype <tt>OpenCL</tt>, <tt>LevelZero</tt>, <tt>CUDA</tt>, or <tt>VectorEngine</tt>.</li>
 <li>GPU: subtype <tt>RSMI</tt> (AMD GPU) or <tt>NVML</tt> (NVIDIA GPU).</li>
 <li>OpenFabrics: subtype <tt>BXI</tt> (Bull/Atos BXI HCA).</li>
+<li>Network: subtype <tt>Slingshot</tt> (HPE Cray Slingshot Cassini HSN).</li>
 <li>Storage: subtype <tt>Disk</tt>, <tt>Tape</tt>, or <tt>Removable Media Device</tt>.</li>
 <li>Memory: <tt>NVM</tt> (non-volatile memory), <tt>SPM</tt> (specific-purpose memory), <tt>CXLMem</tt> (CXL volatile ou persistent memory).</li>
 </ul>

hwloc/topology-linux.c

@@ -6198,6 +6198,15 @@ hwloc_linuxfs_net_class_fillinfos(int root_fd,
       }
     }
   }
+  if (!strncmp(obj->name, "hsn", 3)) {
+    /* Cray Cassini HSN for Slingshot networks are Ethernet-based,
+     * named hsnX with a "cxi" (and "cxi_user") class.
+     */
+    snprintf(path, sizeof(path), "%s/device/cxi", osdevpath);
+    if (!hwloc_access(path, R_OK|X_OK, root_fd)) {
+      obj->subtype = strdup("Slingshot");
+    }
+  }
 }
 
 static int