sched: Detect KIST support at compile time

Add a detection for the KIST scheduler in our build system and set
HAVE_KIST_SUPPORT if available.

Adapt the should use kist function with this new compile option.
Signed-off-by: David Goulet <dgoulet@torproject.org>

configure.ac

@@ -792,6 +792,34 @@ AC_CHECK_MEMBERS([SSL.state], , ,
 [#include <openssl/ssl.h>
 ])
 
+dnl Define the set of checks for KIST scheduler support.
+AC_DEFUN([CHECK_KIST_SUPPORT],[
+  dnl KIST needs struct tcp_info and for certain members to exist.
+  AC_CHECK_MEMBERS(
+    [struct tcp_info.tcpi_unacked, struct tcp_info.tcpi_snd_mss],
+    , ,[[#include <netinet/tcp.h>]])
+  dnl KIST needs SIOCOUTQNSD to exist for an ioctl call.
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
+                     #include <linux/sockios.h>
+                     #ifndef SIOCOUTQNSD
+                     #error
+                     #endif
+                     ])], have_siocoutqnsd=yes, have_siocoutqnsd=no)
+  if test "x$have_siocoutqnsd" = "xyes"; then
+    if test "x$ac_cv_member_struct_tcp_info_tcpi_unacked" = "xyes"; then
+      if test "x$ac_cv_member_struct_tcp_info_tcpi_snd_mss" = "xyes"; then
+        have_kist_support=yes
+      fi
+    fi
+  fi
+])
+dnl Now, trigger the check.
+CHECK_KIST_SUPPORT
+AS_IF([test "x$have_kist_support" = "xyes"],
+      [AC_DEFINE(HAVE_KIST_SUPPORT, 1, [Defined if KIST scheduler is supported
+                                        on this system])],
+      [AC_MSG_NOTICE([KIST scheduler can't be used. Missing support.])])
+
 LIBS="$save_LIBS"
 LDFLAGS="$save_LDFLAGS"
 CPPFLAGS="$save_CPPFLAGS"

src/or/scheduler.c

@@ -215,17 +215,6 @@ get_run_sched_ev(void)
   return run_sched_ev;
 }
 
-/* Return true iff the scheduler subsystem should use KIST. */
-int
-scheduler_should_use_kist(void)
-{
-  int64_t run_freq = kist_scheduler_run_interval();
-  log_info(LD_SCHED, "Determined sched_run_interval should be %" PRId64 ". "
-                     "Will%s use KIST.",
-           run_freq, (run_freq > 0 ? "" : " not"));
-  return run_freq > 0;
-}
-
 /* Comparison function to use when sorting pending channels */
 MOCK_IMPL(int,
 scheduler_compare_channels, (const void *c1_v, const void *c2_v))

src/or/scheduler.h

@@ -116,7 +116,6 @@ MOCK_DECL(void, scheduler_channel_has_waiting_cells, (channel_t *chan));
 /*********************************
  * Defined in scheduler.c
  *********************************/
-int scheduler_should_use_kist(void);
 smartlist_t *get_channels_pending(void);
 struct event *get_run_sched_ev(void);
 MOCK_DECL(int, scheduler_compare_channels,
@@ -156,6 +155,7 @@ MOCK_DECL(int, channel_should_write_to_kernel,
 MOCK_DECL(void, channel_write_to_kernel, (channel_t *chan));
 MOCK_DECL(void, update_socket_info_impl, (socket_table_ent_t *ent));
 
+int scheduler_should_use_kist(void);
 scheduler_t *get_kist_scheduler(void);
 int32_t kist_scheduler_run_interval(const networkstatus_t *ns);
 

src/or/scheduler_kist.c

@@ -588,3 +588,26 @@ kist_scheduler_run_interval(const networkstatus_t *ns)
   return run_interval;
 }
 
+#ifdef HAVE_KIST_SUPPORT
+
+/* Return true iff the scheduler subsystem should use KIST. */
+int
+scheduler_should_use_kist(void)
+{
+  int64_t run_interval = kist_scheduler_run_interval(NULL);
+  log_info(LD_SCHED, "Determined sched_run_interval should be %" PRId64 ". "
+                     "Will%s use KIST.",
+           run_interval, (run_interval > 0 ? "" : " not"));
+  return run_interval > 0;
+}
+
+#else /* HAVE_KIST_SUPPORT */
+
+int
+scheduler_should_use_kist(void)
+{
+  return 0;
+}
+
+#endif /* HAVE_KIST_SUPPORT */
+