OS-5804 lxbrand needs support for CLOCK_*_CPUTIME_ID timers

*** 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.
   */
  
  /*
   * 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.
   *
   * 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.
   */
  
--- 8,38 ----
   * source.  A copy of the CDDL is also available via the Internet at
   * http://www.illumos.org/license/CDDL.
   */
  
  /*
!  * 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 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.
   */
  
*** 81,92 ****
              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 */
          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 */
  };
--- 88,99 ----
              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_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 */
  };