linux/dax: add CXLDevice info attribute(s) in DAX and NUMA nodes

There can be multiple entries if the region is interleaved.
Might be better to merge into a single info attr? We'll see.

This uses "memregion" identifiers (regionX) to match dax devices
and CXL devices.

The corresponding Linux code (CXL volatile regions, etc) is
planned for Linux 6.3.

Refs #554

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

doc/hwloc.doxy

@@ -2127,6 +2127,11 @@ and GID #1 of port #3.
 These info attributes are attached to objects specified in parentheses.
 
 <dl>
+<dt>CXLDevice (NUMA Nodes or DAX Memory OS devices)</dt>
+<dd>The PCI/CXL bus ID of a device whose CXL Type-3 memory is exposed here.
+There may be multiple instances of this attributes if multiple device memories
+are interleaved.
+</dd>
 <dt>DAXDevice (NUMA Nodes)</dt>
 <dd>The name of the Linux DAX device that was used to expose a non-volatile
 memory region as a volatile NUMA node.

hwloc/topology-linux.c

@@ -3690,6 +3690,69 @@ read_node_mscaches(struct hwloc_topology *topology,
   return 0;
 }
 
+static int
+annotate_cxl_dax(hwloc_obj_t obj, unsigned region, int root_fd)
+{
+  char path[300];
+  unsigned i;
+
+  for(i=0; ; i++) {
+    char decoder[20]; /* "decoderX.Y" */
+    char decoderpath[256], *endpoint;
+    char uportpath[256], *pcirootbus, *pcibdf;
+    unsigned pcidomain, pcibus, pcidevice, pcifunc;
+    char *slash, *end;
+    int err;
+
+    /* read the i-th decoder name from file target<i> */
+    snprintf(path, sizeof(path), "/sys/bus/cxl/devices/region%u/target%u", region, i);
+    if (hwloc_read_path_by_length(path, decoder, sizeof(decoder), root_fd) < 0)
+      break;
+    end = strchr(decoder, '\n');
+    if (end)
+      *end = '\0';
+    hwloc_debug("hwloc/dax/cxl: found decoder `%s' for region#%u target#%u\n", decoder, region, i);
+
+    /* get the endpoint symlink which ends with "/portT/endpointX/decoderY.X/" */
+    snprintf(path, sizeof(path), "/sys/bus/cxl/devices/%s", decoder);
+    err = hwloc_readlink(path, decoderpath, sizeof(decoderpath), root_fd);
+    if (err < 0)
+      break;
+    endpoint = strstr(decoderpath, "endpoint");
+    if (!endpoint)
+      break;
+    slash = strchr(endpoint, '/');
+    if (!slash)
+      break;
+    *slash = '\0';
+    hwloc_debug("hwloc/dax/cxl: found endpoint `%s'\n", endpoint);
+
+    /* get the PCI in the endpointX/uport symlink "../../../pci<busid>/<BDFs>../memX" */
+    snprintf(path, sizeof(path), "/sys/bus/cxl/devices/%s/uport", endpoint);
+    err = hwloc_readlink(path, uportpath, sizeof(uportpath), root_fd);
+    if (err < 0)
+      break;
+    hwloc_debug("hwloc/dax/cxl: lookind for BDF at the end of uport `%s'\n", uportpath);
+    pcirootbus = strstr(uportpath, "/pci");
+    if (!pcirootbus)
+      break;
+    slash = pcirootbus + 11; /* "/pciXXXX:YY/" */
+    if (*slash != '/')
+      break;
+    pcibdf = NULL;
+    while (sscanf(slash, "/%x:%x:%x.%x/", &pcidomain, &pcibus, &pcidevice, &pcifunc) == 4) {
+      pcibdf = slash+1;
+      slash += 13;
+    }
+    *slash = '\0';
+    if (pcibdf) {
+      hwloc_obj_add_info(obj, "CXLDevice", pcibdf);
+    }
+  }
+
+  return 0;
+}
+
 static int
 dax_is_kmem(const char *name, int fsroot_fd)
 {
@@ -3705,7 +3768,7 @@ annotate_dax_parent(hwloc_obj_t obj, const char *name, int fsroot_fd)
 {
   char daxpath[300];
   char link[PATH_MAX];
-  char *begin, *end;
+  char *begin, *end, *region;
   const char *type;
   int err;
 
@@ -3745,6 +3808,14 @@ annotate_dax_parent(hwloc_obj_t obj, const char *name, int fsroot_fd)
   type = strstr(begin, "ndbus") ? "NVM" : "SPM";
   hwloc_obj_add_info(obj, "DAXType", type);
 
+  /* try to get some CXL info from the region */
+  region = strstr(begin, "/region");
+  if (region) {
+    unsigned i = strtoul(region+7, &end, 10);
+    if (end != region+7)
+      annotate_cxl_dax(obj, i, fsroot_fd);
+  }
+
   /* insert DAXParent last because it's likely less useful than others */
   hwloc_obj_add_info(obj, "DAXParent", begin);