test: Add oneshot mode to fast page fault helper

Add option for fast_page_fault_helper to run in a oneshot mode, that
doesn't require the signal to be triggered before measuring the fault
latency.

This makes it possible to test fault latency on non-snapshotted vms as
only the first fault is measured.

Signed-off-by: Jack Thomson <jackabt@amazon.com>

Author: JackThomson2

resources/overlay/usr/local/bin/fast_page_fault_helper.c

@@ -16,6 +16,7 @@
 #include <sys/mman.h> // mmap
 #include <time.h>     // clock_gettime
 #include <fcntl.h>    // open
+#include <getopt.h>   // getopt
 
 #define MEM_SIZE_MIB (128 * 1024 * 1024)
 #define NANOS_PER_SEC 1000000000
@@ -30,20 +31,39 @@ void touch_memory(void *mem, size_t size, char val) {
 
 int main() {
     sigset_t set;
-    int signal;
+    int signal, character;
     void *ptr;
     struct timespec start, end;
     long duration_nanos;
     FILE *out_file;
 
-    sigemptyset(&set);
-    if (sigaddset(&set, SIGUSR1) == -1) {
-        perror("sigaddset");
-        return 1;
+    char *options = 0;
+    int longindex = 0;
+    int signal_wait = 1;
+
+    struct option longopts[] = {
+      {"nosignal", no_argument, NULL, 's'},
+      {NULL, 0, NULL, 0}
+    };
+
+    while((character = getopt_long(argc, argv, "s", longopts, &longindex)) != -1) {
+      switch (character) {
+        case 's':
+          signal_wait = 0;
+          break;
+      }
     }
-    if (sigprocmask(SIG_BLOCK, &set, NULL) == -1)  {
-        perror("sigprocmask");
-        return 1;
+
+    if (signal_wait) {
+      sigemptyset(&set);
+      if (sigaddset(&set, SIGUSR1) == -1) {
+          perror("sigaddset");
+          return 1;
+      }
+      if (sigprocmask(SIG_BLOCK, &set, NULL) == -1)  {
+          perror("sigprocmask");
+          return 1;
+      }
     }
 
     ptr = mmap(NULL, MEM_SIZE_MIB, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
@@ -53,9 +73,11 @@ int main() {
         return 1;
     }
 
-    touch_memory(ptr, MEM_SIZE_MIB, 1);
+    if (signal_wait) {
+      touch_memory(ptr, MEM_SIZE_MIB, 1);
 
-    sigwait(&set, &signal);
+      sigwait(&set, &signal);
+    }
 
     clock_gettime(CLOCK_BOOTTIME, &start);
     touch_memory(ptr, MEM_SIZE_MIB, 2);
@@ -76,4 +98,4 @@ int main() {
     }
 
     return 0;
-}
+}