OS-5804 lxbrand needs support for CLOCK_*_CPUTIME_ID timers

@@ -8,24 +8,31 @@
  * source.  A copy of the CDDL is also available via the Internet at
  * http://www.illumos.org/license/CDDL.
  */
 
 /*
- * Copyright 2016 Joyent, Inc.
+ * Copyright 2020 Joyent, Inc.
  */
 
 /*
  * The illumos kernel provides two clock backends: CLOCK_REALTIME, the
  * adjustable system wall clock; and CLOCK_HIGHRES, the monotonically
  * increasing time source that is not subject to drift or adjustment.  By
  * contrast, the Linux kernel is furnished with an overabundance of narrowly
  * differentiated clock types.
  *
- * Fortunately, most of the commonly used Linux clock types are either similar
- * enough to the native clock backends that they can be directly mapped, or
- * represent queries to the per-process and per-LWP microstate counters.
+ * Fortunately, most of the commonly used Linux clock types are similar
+ * enough to the native clock backends that they can be directly mapped.
  *
+ * Unfortunately, while CLOCK_{THREAD,PROCESS}_CPUTIME_ID are *somewhat*
+ * implemented in the main illumos kernel as itimers (see setitimer(2)), we
+ * would need to entirely bringup of CLOCK_{THREAD,PROCESS}_CPUTIME_ID to
+ * implement timer_create() and friends.  For now, we opt to map it to
+ * CLOCK_HIGHRES for timer_create() and friends, but continue to emulate
+ * more-accurate queries to per-process or per-LWP microstate accounting for
+ * getres, gettime, or settime.
+ *
  * CLOCK_BOOTTIME is identical to CLOCK_MONOTONIC, except that it takes into
  * account time that the system is suspended. Since that is uninteresting to
  * us, we treat it the same.
  */
 

@@ -81,12 +88,12 @@
             lx_emul_clock_settime }
 
 static lx_clock_backend_t lx_clock_backends[] = {
         NATIVE(CLOCK_REALTIME),         /* LX_CLOCK_REALTIME */
         NATIVE(CLOCK_HIGHRES),          /* LX_CLOCK_MONOTONIC */
-        EMUL(CLOCK_PROCESS_CPUTIME_ID), /* LX_CLOCK_PROCESS_CPUTIME_ID */
-        EMUL(CLOCK_THREAD_CPUTIME_ID),  /* LX_CLOCK_THREAD_CPUTIME_ID */
+        EMUL(CLOCK_HIGHRES),            /* LX_CLOCK_PROCESS_CPUTIME_ID */
+        EMUL(CLOCK_HIGHRES),            /* LX_CLOCK_THREAD_CPUTIME_ID */
         NATIVE(CLOCK_HIGHRES),          /* LX_CLOCK_MONOTONIC_RAW */
         NATIVE(CLOCK_REALTIME),         /* LX_CLOCK_REALTIME_COARSE */
         NATIVE(CLOCK_HIGHRES),          /* LX_CLOCK_MONOTONIC_COARSE */
         NATIVE(CLOCK_HIGHRES)           /* LX_CLOCK_BOOTTIME */
 };