Tidy up ld preload hacks

tests/acceptance/ld_preloads/msync_logger.c

@@ -0,0 +1,33 @@
+#define _GNU_SOURCE
+
+#include <dlfcn.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+
+typedef int (*real_msync_t)(void *addr, size_t length, int flags);
+
+int real_msync(void *addr, size_t length, int flags) {
+  return ((real_msync_t)dlsym(RTLD_NEXT, "msync"))(addr, length, flags);
+}
+
+/*
+ * Noddy LD_PRELOAD wrapper to catch msync calls, and log them to a file.
+ */
+
+int msync(void *addr, size_t length, int flags) {
+  FILE *fd;
+  char *fn;
+  int retval;
+  
+  retval = real_msync(addr, length, flags);
+  
+  fn = getenv("OUTPUT_msync_logger");
+  if ( fn != NULL ) {
+    fd = fopen(fn,"a");
+    fprintf(fd,"msync:%d:%i:%i:%i\n", addr, length, flags, retval);
+    fclose(fd);
+  }
+
+  return retval;
+}