shell: add hwloc plugin with support for -o hwloc.xmlfile

Problem: Some use cases may benefit from stashing the job shell's copy
of hwloc in a file referenced by HWLOC_XMLFILE, which causes hwloc
to load topology from a file instead of discovering the topology
from scratch.

Add a new hwloc builtin plugin for handling optional behavior related
to hwloc. Add initial support for writing shell XML to a file and
setting HWLOC_XMLFILE if `-o hwloc.xmlfile` is used. Other `hwloc.`
keys are reserved for possible future use.

The plugin checks for hwloc.xmlfile in shell.post-init, which allows
other shell plugins to set this option if required during shell.init
or before without worrying about plugin loading order.

Author: grondo

src/shell/Makefile.am

@@ -92,7 +92,8 @@ flux_shell_SOURCES = \
 	cyclic.c \
 	signal.c \
 	files.c \
-	oom.c
+	oom.c \
+	hwloc.c
 
 flux_shell_LDADD = \
 	$(builddir)/libshell.la \

src/shell/builtins.c

@@ -51,6 +51,7 @@ extern struct shell_builtin builtin_rlimit;
 extern struct shell_builtin builtin_cyclic;
 extern struct shell_builtin builtin_signal;
 extern struct shell_builtin builtin_oom;
+extern struct shell_builtin builtin_hwloc;
 
 static struct shell_builtin * builtins [] = {
     &builtin_tmpdir,
@@ -74,6 +75,7 @@ static struct shell_builtin * builtins [] = {
     &builtin_cyclic,
     &builtin_signal,
     &builtin_oom,
+    &builtin_hwloc,
     &builtin_list_end,
 };
 

src/shell/hwloc.c

@@ -0,0 +1,99 @@
+/************************************************************\
+ * Copyright 2024 Lawrence Livermore National Security, LLC
+ * (c.f. AUTHORS, NOTICE.LLNS, COPYING)
+ *
+ * This file is part of the Flux resource manager framework.
+ * For details, see https://github.com/flux-framework.
+ *
+ * SPDX-License-Identifier: LGPL-3.0
+\************************************************************/
+
+/* hwloc options handler
+ */
+#define FLUX_SHELL_PLUGIN_NAME "hwloc"
+
+#if HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <flux/core.h>
+#include <flux/shell.h>
+
+#include "src/common/libutil/read_all.h"
+#include "ccan/str/str.h"
+
+#include "builtins.h"
+
+static int create_xmlfile (flux_shell_t *shell)
+{
+    int fd = -1;
+    char *xmlfile = NULL;
+    const char *hwloc_xml;
+    const char *tmpdir;
+
+    if (!(tmpdir = flux_shell_getenv (shell, "FLUX_JOB_TMPDIR")))
+        tmpdir = "/tmp";
+
+    if (flux_shell_get_hwloc_xml (shell, &hwloc_xml) < 0) {
+        shell_log_error ("failed to get shell hwloc xml");
+        goto error;
+    }
+    if (asprintf (&xmlfile, "%s/hwloc.xml", tmpdir) < 0) {
+        shell_log_error ("asprintf HWLOC_XMLFILE failed");
+        goto error;
+    }
+    if ((fd = open (xmlfile, O_CREAT|O_EXCL|O_WRONLY, 0640)) < 0) {
+        shell_log_errno ("%s", xmlfile);
+        goto error;
+    }
+    shell_debug ("Writing %ld bytes to HWLOC_XMLFILE=%s\n",
+                 (long int) strlen (hwloc_xml),
+                 xmlfile);
+    if (write_all (fd, hwloc_xml, strlen (hwloc_xml)) < 0 || close (fd) < 0) {
+        shell_log_errno ("failed to write HWLOC_XMLFILE");
+        goto error;
+    }
+    if (flux_shell_setenvf (shell, 0, "HWLOC_XMLFILE", "%s", xmlfile) < 0) {
+        shell_log_errno ("failed to set HWLOC_XMLFILE in job environment");
+        goto error;
+    }
+    return 0;
+error:
+    if (fd >= 0)
+        close (fd);
+    free (xmlfile);
+    return -1;
+}
+
+static int hwloc_post_init (flux_plugin_t *p,
+                            const char *topic,
+                            flux_plugin_arg_t *args,
+                            void *data)
+{
+    flux_shell_t *shell = flux_plugin_get_shell (p);
+    int xmlfile = 0;
+
+    if (flux_shell_getopt_unpack (shell,
+                                  "hwloc",
+                                  "{s?i}",
+                                    "xmlfile", &xmlfile) < 0)
+        return shell_log_errno ("failed to unpack hwloc options");
+
+    if (xmlfile && create_xmlfile (shell) < 0)
+        return shell_log_errno ("failed to write HWLOC_XMLFILE");
+    return 0;
+}
+
+struct shell_builtin builtin_hwloc = {
+    .name      = FLUX_SHELL_PLUGIN_NAME,
+    .post_init = hwloc_post_init,
+};
+
+/*
+ * vi:tabstop=4 shiftwidth=4 expandtab
+ */