fix: spurious errors/warnings from a pc13v HA deploy (bug-1872..1877)

- bug-1872 (worker): "Failed to find any disk statistics in
  /proc/diskstats" ERROR every 15 s on an NVMe-only host. The whole-disk
  filter guessed from the name and skipped anything ending in a digit or
  containing 'p' -- every nvmeXnY, mmcblkN, even sdp -- so io was never
  reported. diskstats.h now counts a device only when
  /sys/block/<name>/device exists (real disks; not partitions, loop, dm,
  md, zram), and a host with no disk warns once.
- bug-1873 (worker): "Failed to get worker pid" WARN on job start. MainPID
  reads 0 until systemd has forked the new transient unit; xcecd.c already
  retries, so the miss is DEBUG and the final failure names the unit.
- bug-1874 (scheduler): deprecation WARN for the legacy xce_sched_fcfs on
  every start, though builtin_fcfs is the picker. Registration still wraps
  a job_elect_fn plugin but no longer warns; selecting one warns once.
- bug-1875 (apiserver): "Not running as root -- PAM authentication will not
  work" with the default provider config_file; now only for provider pam.
- bug-1876 (controller): standbys logged "cluster_init_phase2 ... failed
  (rc=-22)" WARN every 3 s while waiting for the primary's config push,
  a state the function itself calls normal. It returns -EAGAIN for that
  wait; callers log it at INFO, other failures still WARN.
- bug-1877 (controller): "WAL/snapshot stored unencrypted" warned without
  looking. persist_path_encrypted() checks fscrypt (statx) and dm-crypt
  (sysfs dm/uuid CRYPT-, through LVM slaves); the warning stays when the
  storage is not shown to be encrypted (e.g. a plain /tmp).

Tests: worker diskstats_test (2 of 4 RED on the old filter with pc13v's
/proc/diskstats), controller test_phase2_cold_boot and
test_persist_encryption, scheduler picker tests, apiserver
TestRootWarning. Full ASAN build: all 113 suites pass (controller 319/0,
harness 141/0).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/scheduler/include/plugin.h

@@ -99,6 +99,12 @@ typedef struct {
      * matching) reads `core`, never `sched`, so it works identically
      * whichever registration path registered it. */
     xce_sched_core_t* core;
+    /* bug-1874: set by plugin_register() when it adapted a job_elect_fn-only
+     * plugin via the legacy wrapper; the deprecation is reported (once,
+     * legacy_picker_warned) when such a plugin is SELECTED as the picker,
+     * not merely registered. */
+    int legacy_picker;
+    int legacy_picker_warned;
 } xce_sched_plugin_t;
 
 extern int  plugin_register(void*, void*);

src/scheduler/src/plugin.c

@@ -146,11 +146,11 @@ int plugin_register(void* arg1, void* arg2)
      * registration time (Req 5 "Migration from old job_elect_fn"). A
      * plugin that already provides picker_iface is left untouched. */
     if ((plugin->picker_iface == NULL) && (plugin->job_elect_fn != NULL)) {
-        plugin->picker_iface = &legacy_picker_wrapper_iface;
-        WARN("plugin '%s' selects jobs via the deprecated job_elect_fn "
-             "hook; migrate to xce_job_picker_iface_t (scheduler-core spec, "
-             "Req 5 'Migration from old job_elect_fn')",
-             plugin->name);
+        plugin->picker_iface  = &legacy_picker_wrapper_iface;
+        plugin->legacy_picker = 1;
+        /* bug-1874: no warning here -- the legacy "xce_sched_fcfs" is
+         * registered on every start but is not the normal-mode picker;
+         * sched_resolve_job_picker() warns when one is actually selected. */
     }
 
     if (plugin->init_fn != NULL) {

src/scheduler/src/schedobj.c

@@ -440,6 +440,14 @@ int sched_resolve_job_picker(xce_sched_core_t* core, xce_sched_plugin_t** out)
         return -EINVAL;
     }
 
+    if (plugin->legacy_picker && !plugin->legacy_picker_warned) {
+        plugin->legacy_picker_warned = 1;
+        WARN("job picker '%s' selects jobs via the deprecated job_elect_fn "
+             "hook; migrate to xce_job_picker_iface_t (scheduler-core spec, "
+             "Req 5 'Migration from old job_elect_fn')",
+             plugin->name);
+    }
+
     *out = plugin;
 
     return 0;

src/scheduler/testsuite/test_picker_wiring.c

@@ -375,6 +375,33 @@ static void test_registered_but_not_a_picker_fails_with_einval_not_enoent(void)
     TEST_ASSERT_NULL(resolved);
 }
 
+/* bug-1874: plugin_register() warned about the deprecated job_elect_fn hook
+ * for every legacy plugin it wrapped -- so the legacy "xce_sched_fcfs",
+ * registered on every scheduler start but never the normal-mode picker
+ * (builtin_fcfs is), logged a deprecation WARN on every start. The warning
+ * belongs to selecting such a plugin as the picker, and only once. */
+static void
+test_legacy_picker_deprecation_flagged_on_selection_not_registration(void)
+{
+    xce_scheduler_t     sched;
+    xce_sched_plugin_t* legacy   = NULL;
+    xce_sched_plugin_t* resolved = NULL;
+
+    fixture_init(&sched);
+    legacy = make_legacy_plugin("legacy_picker_1874");
+    TEST_ASSERT_GREATER_OR_EQUAL(0, plugin_register(&sched, legacy));
+    TEST_ASSERT_NOT_NULL_MESSAGE(legacy->picker_iface,
+                                 "still adapted to the picker interface");
+    TEST_ASSERT_FALSE_MESSAGE(legacy->legacy_picker_warned,
+                              "registration alone must not warn");
+
+    sched.core.job_pick_plugin = "legacy_picker_1874";
+    TEST_ASSERT_EQUAL_INT(0, sched_resolve_job_picker(&sched.core, &resolved));
+    TEST_ASSERT_EQUAL_PTR(legacy, resolved);
+    TEST_ASSERT_TRUE_MESSAGE(legacy->legacy_picker_warned,
+                             "selecting it as the picker warns");
+}
+
 /* Unset job_pick_plugin, and the caller never called
  * sched_set_default_job_pick_plugin() either -- -EINVAL (scheduler.h's
  * documented contract), distinct from both cases above. */
@@ -504,5 +531,7 @@ int main(void)
     RUN_TEST(
         test_resolved_builtin_fcfs_has_job_elect_fn_null_selecting_native_branch);
     RUN_TEST(test_legacy_and_native_pickers_coexist_and_resolve_independently);
+    RUN_TEST(
+        test_legacy_picker_deprecation_flagged_on_selection_not_registration);
     return UNITY_END();
 }

src/scheduler/testsuite/test_plugin_picker_registration.c

@@ -139,10 +139,13 @@ static void legacy_plugin_init(xce_sched_plugin_t* plugin, char* name)
 }
 
 /* Req 5 "Migration from old job_elect_fn": an old-style, job_elect_fn-only
- * plugin registers successfully via the compatibility wrapper and logs a
- * deprecation warning exactly once, at registration time. */
+ * plugin registers successfully via the compatibility wrapper. bug-1874:
+ * registration itself no longer warns -- the legacy "xce_sched_fcfs" is
+ * registered on every start without being the picker; the deprecation is
+ * reported when such a plugin is selected (sched_resolve_job_picker(), see
+ * test_picker_wiring.c). */
 static void
-test_register_legacy_job_elect_fn_only_plugin_uses_wrapper_and_warns(void)
+test_register_legacy_job_elect_fn_only_plugin_uses_wrapper_without_warning(void)
 {
     xce_scheduler_t    sched;
     xce_sched_plugin_t plugin;
@@ -156,7 +159,9 @@ test_register_legacy_job_elect_fn_only_plugin_uses_wrapper_and_warns(void)
     stop_log_capture();
 
     TEST_ASSERT_GREATER_OR_EQUAL(0, rc);
-    TEST_ASSERT_EQUAL_INT(1, g_warn_count);
+    TEST_ASSERT_EQUAL_INT(0, g_warn_count);
+    TEST_ASSERT_TRUE(plugin.legacy_picker);
+    TEST_ASSERT_FALSE(plugin.legacy_picker_warned);
     TEST_ASSERT_NOT_NULL(plugin.picker_iface);
     TEST_ASSERT_EQUAL_PTR(&legacy_picker_wrapper_iface, plugin.picker_iface);
 }
@@ -243,7 +248,7 @@ int main(void)
 {
     UNITY_BEGIN();
     RUN_TEST(
-        test_register_legacy_job_elect_fn_only_plugin_uses_wrapper_and_warns);
+        test_register_legacy_job_elect_fn_only_plugin_uses_wrapper_without_warning);
     RUN_TEST(test_legacy_wrapper_next_job_calls_job_elect_fn);
     RUN_TEST(
         test_register_new_style_picker_plugin_skips_wrapper_and_does_not_warn);