sys_linux: drop support for kernels before 2.6.39

Linux 2.6.39 was released in 2011.

Refuse to start if a kernel version before 2.6.39 is detected. Assume
the ADJ_SETOFFSET adjtimex mode is always supported. Its verification
briefly reset the timex maxerror value to 0, which possibly confused
applications checking the value at that moment.

Drop the unneeded workaround for slow frequency updates in versions
2.6.27-2.6.32.

diff --git a/sys_linux.c b/sys_linux.c
index 8373e250e102123ee78eb93c8e3179740fd18e22..febf0eb7f61153dd9aa3c27108b6f33cdbd7236e 100644 (file)
--- a/sys_linux.c
+++ b/sys_linux.c
@@ -96,9 +96,6 @@ static int max_tick_bias;
 static int hz;
 static double dhz; /* And dbl prec version of same for arithmetic */
 
-/* Flag indicating whether adjtimex() can step the clock */
-static int have_setoffset;
-
 /* The assumed rate at which the effective frequency and tick values are
    updated in the kernel */
 static int tick_update_hz;
@@ -298,16 +295,11 @@ get_version_specific_details(void)
   get_kernel_version(&major, &minor, &patch);
   DEBUG_LOG("Linux kernel major=%d minor=%d patch=%d", major, minor, patch);
 
-  if (kernelvercmp(major, minor, patch, 2, 2, 0) < 0) {
+  if (kernelvercmp(major, minor, patch, 2, 6, 39) < 0) {
     LOG_FATAL("Kernel version not supported, sorry.");
   }
 
-  if (kernelvercmp(major, minor, patch, 2, 6, 27) >= 0 &&
-      kernelvercmp(major, minor, patch, 2, 6, 33) < 0) {
-    /* In tickless kernels before 2.6.33 the frequency is updated in
-       a half-second interval */
-    tick_update_hz = 2;
-  } else if (kernelvercmp(major, minor, patch, 4, 19, 0) < 0) {
+  if (kernelvercmp(major, minor, patch, 4, 19, 0) < 0) {
     /* In kernels before 4.19 the frequency is updated only on internal ticks
        (CONFIG_HZ).  As their rate cannot be reliably detected from the user
        space, and it may not even be constant (CONFIG_NO_HZ - aka tickless),
@@ -315,13 +307,6 @@ get_version_specific_details(void)
     tick_update_hz = 100;
   }
 
-  /* ADJ_SETOFFSET support */
-  if (kernelvercmp(major, minor, patch, 2, 6, 39) < 0) {
-    have_setoffset = 0;
-  } else {
-    have_setoffset = 1;
-  }
-
   DEBUG_LOG("hz=%d nominal_tick=%d max_tick_bias=%d tick_update_hz=%d",
             hz, nominal_tick, max_tick_bias, tick_update_hz);
 }
@@ -342,34 +327,6 @@ reset_adjtime_offset(void)
 
 /* ================================================== */
 
-static int
-test_step_offset(void)
-{
-  struct timex txc;
-
-  /* Zero maxerror and check it's reset to a maximum after ADJ_SETOFFSET.
-     This seems to be the only way how to verify that the kernel really
-     supports the ADJ_SETOFFSET mode as it doesn't return an error on unknown
-     mode. */
-
-  txc.modes = MOD_MAXERROR;
-  txc.maxerror = 0;
-
-  if (SYS_Timex_Adjust(&txc, 1) < 0 || txc.maxerror != 0)
-    return 0;
-
-  txc.modes = ADJ_SETOFFSET | ADJ_NANO;
-  txc.time.tv_sec = 0;
-  txc.time.tv_usec = 0;
-
-  if (SYS_Timex_Adjust(&txc, 1) < 0 || txc.maxerror < 100000)
-    return 0;
-
-  return 1;
-}
-
-/* ================================================== */
-
 static void
 report_time_adjust_blockers(void)
 {
@@ -392,15 +349,10 @@ SYS_Linux_Initialise(void)
 
   reset_adjtime_offset();
 
-  if (have_setoffset && !test_step_offset()) {
-    LOG(LOGS_INFO, "adjtimex() doesn't support ADJ_SETOFFSET");
-    have_setoffset = 0;
-  }
-
   SYS_Timex_InitialiseWithFunctions(1.0e6 * max_tick_bias / nominal_tick,
                                     1.0 / tick_update_hz,
                                     read_frequency, set_frequency,
-                                    have_setoffset ? apply_step_offset : NULL,
+                                    apply_step_offset,
                                     0.0, 0.0, NULL, NULL);
 }