From ebf57dfc03c9f3bda5ee065d45c28feb6ebb1c97 Mon Sep 17 00:00:00 2001
From: Dirk Engling <erdgeist@erdgeist.org>
Date: Fri, 30 Oct 2026 03:25:35 +0100
Subject: Reduce syscalls and add helper to count them

---
 tests/syscount.c | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 tests/syscount.c

(limited to 'tests/syscount.c')

diff --git a/tests/syscount.c b/tests/syscount.c
new file mode 100644
index 0000000..ec45c15
--- /dev/null
+++ b/tests/syscount.c
@@ -0,0 +1,144 @@
+/* Counts the system calls a run makes, by standing in front of libc.
+
+     cc -O2 -shared -fPIC -o syscount.so tests/syscount.c -ldl
+     LD_PRELOAD=./syscount.so ./opentracker -f conf      (DYLD_INSERT_LIBRARIES on macOS)
+
+   The tally goes to stderr when the process exits. Reading the source tells
+   you which calls a path should make; this tells you which it does make,
+   which is not always the same thing. */
+
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <stdarg.h>
+#include <stdatomic.h>
+#include <stdio.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifdef __linux__
+#include <sys/epoll.h>
+#endif
+
+#define COUNTER(name) static _Atomic long g_##name
+#define BUMP(name)    atomic_fetch_add_explicit(&g_##name, 1, memory_order_relaxed)
+#define REPORT(name)  fprintf(stderr, "  %-14s %10ld\n", #name, atomic_load(&g_##name))
+
+COUNTER(accept);
+COUNTER(accept4);
+COUNTER(read);
+COUNTER(write);
+COUNTER(close);
+COUNTER(fcntl);
+COUNTER(recvfrom);
+COUNTER(sendto);
+COUNTER(epoll_ctl);
+COUNTER(epoll_wait);
+
+typedef int (*fn_accept)(int, struct sockaddr *, socklen_t *);
+typedef int (*fn_accept4)(int, struct sockaddr *, socklen_t *, int);
+typedef ssize_t (*fn_read)(int, void *, size_t);
+typedef ssize_t (*fn_write)(int, const void *, size_t);
+typedef int (*fn_close)(int);
+typedef int (*fn_fcntl)(int, int, ...);
+typedef ssize_t (*fn_recvfrom)(int, void *, size_t, int, struct sockaddr *, socklen_t *);
+typedef ssize_t (*fn_sendto)(int, const void *, size_t, int, const struct sockaddr *, socklen_t);
+
+static fn_accept   real_accept;
+static fn_accept4  real_accept4;
+static fn_read     real_read;
+static fn_write    real_write;
+static fn_close    real_close;
+static fn_fcntl    real_fcntl;
+static fn_recvfrom real_recvfrom;
+static fn_sendto   real_sendto;
+
+/* Resolving lazily keeps the library out of the way until something is
+   actually called, which matters because dlsym itself allocates */
+#define WRAP(name)                                                                                                     \
+  if (!real_##name)                                                                                                    \
+    real_##name = (fn_##name)dlsym(RTLD_NEXT, #name);                                                                  \
+  BUMP(name)
+
+int accept(int s, struct sockaddr *addr, socklen_t *len) {
+  WRAP(accept);
+  return real_accept(s, addr, len);
+}
+
+#ifdef SOCK_NONBLOCK
+int accept4(int s, struct sockaddr *addr, socklen_t *len, int flags) {
+  WRAP(accept4);
+  return real_accept4(s, addr, len, flags);
+}
+#endif
+
+ssize_t read(int fd, void *buf, size_t count) {
+  WRAP(read);
+  return real_read(fd, buf, count);
+}
+
+ssize_t write(int fd, const void *buf, size_t count) {
+  WRAP(write);
+  return real_write(fd, buf, count);
+}
+
+int close(int fd) {
+  WRAP(close);
+  return real_close(fd);
+}
+
+int fcntl(int fd, int cmd, ...) {
+  va_list args;
+  long    arg;
+
+  va_start(args, cmd);
+  arg = va_arg(args, long);
+  va_end(args);
+  WRAP(fcntl);
+  return real_fcntl(fd, cmd, arg);
+}
+
+ssize_t recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen) {
+  WRAP(recvfrom);
+  return real_recvfrom(s, buf, len, flags, from, fromlen);
+}
+
+ssize_t sendto(int s, const void *buf, size_t len, int flags, const struct sockaddr *to, socklen_t tolen) {
+  WRAP(sendto);
+  return real_sendto(s, buf, len, flags, to, tolen);
+}
+
+#ifdef __linux__
+typedef int (*fn_epoll_ctl)(int, int, int, struct epoll_event *);
+typedef int (*fn_epoll_wait)(int, struct epoll_event *, int, int);
+static fn_epoll_ctl  real_epoll_ctl;
+static fn_epoll_wait real_epoll_wait;
+
+int epoll_ctl(int ep, int op, int fd, struct epoll_event *ev) {
+  WRAP(epoll_ctl);
+  return real_epoll_ctl(ep, op, fd, ev);
+}
+
+int epoll_wait(int ep, struct epoll_event *events, int max, int timeout) {
+  WRAP(epoll_wait);
+  return real_epoll_wait(ep, events, max, timeout);
+}
+#endif
+
+__attribute__((destructor)) static void report(void) {
+  fprintf(stderr, "\n  system calls this run\n");
+  REPORT(accept);
+#ifdef SOCK_NONBLOCK
+  REPORT(accept4);
+#endif
+  REPORT(read);
+  REPORT(write);
+  REPORT(close);
+  REPORT(fcntl);
+  REPORT(recvfrom);
+  REPORT(sendto);
+#ifdef __linux__
+  REPORT(epoll_ctl);
+  REPORT(epoll_wait);
+#endif
+}
-- 
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