Add simple benchmark

.gitignore

@@ -1,6 +1,7 @@
 build/
 .cache/
 tests_general
+benchmark
 .copycat.conf
 
 # Created by https://www.toptal.com/developers/gitignore/api/c,cmake

tests/benchmark.c

@@ -0,0 +1,79 @@
+#define _GNU_SOURCE
+
+#include <assert.h>
+#include <fcntl.h>
+#include <linux/openat2.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <time.h>
+#include <unistd.h>
+
+void check_correct_fd(int fd) {
+	assert(fd >= 0);
+	static char c;
+
+	// we should be able to read from the file descriptor
+	ssize_t r = read(fd, &c, 1);
+	assert(r);
+
+	// the read char should be either 'a' or 'b' or 'c', depending on whether system calls are intercepted and which file is read
+	assert((c == 'a') || (c == 'b') || (c == 'c'));
+
+	// close the descriptor again
+	int a = close(fd);
+	assert(!a);
+}
+
+int do_openat(const char *filename) {
+	return openat(0, filename, O_RDONLY);
+}
+
+// we need to do a benchmark without system calls involved, to check for general performance overhead
+int is_prime(int n) {
+	for (int i = 2; i < sqrt(n); ++i) {
+		if ((n % i) == 0) {
+			return 0;
+		}
+	}
+	return 1;
+}
+
+int main(int argc, char *argv[])
+{
+	const char hot_filename[] = "/tmp/a";
+	const char cold_filename[] = "/tmp/c";
+	int f = -1;
+	size_t n = 1000;
+	struct timespec start, end;
+
+	// hot path, every call is intercepted and changed
+	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+	for (size_t i = 0; i < n; ++i) {
+		f = do_openat(hot_filename);
+		check_correct_fd(f);
+	}
+	clock_gettime(CLOCK_MONOTONIC_RAW, &end);
+	printf("openat (intercepted and modified): %lu us\n", (end.tv_sec - start.tv_sec) * 1000000 + (end.tv_nsec - start.tv_nsec) / 1000);
+
+	// cold path, every call is intercepted but no arguments are changed (the BPF filter does not trigger)
+	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+	for (size_t i = 0; i < n; ++i) {
+		f = do_openat(cold_filename);
+		check_correct_fd(f);
+	}
+	clock_gettime(CLOCK_MONOTONIC_RAW, &end);
+	printf("openat (intercepted and not modified): %lu us\n", (end.tv_sec - start.tv_sec) * 1000000 + (end.tv_nsec - start.tv_nsec) / 1000);
+
+	// passive path, no call is intercepted (no system calls)
+	int primes = 0;
+	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+	for (int i = 0; i < n; ++i) {
+		primes += is_prime(i);
+	}
+	clock_gettime(CLOCK_MONOTONIC_RAW, &end);
+	printf("path with no system calls: Found %d primes in %lu us\n", primes, (end.tv_sec - start.tv_sec) * 1000000 + (end.tv_nsec - start.tv_nsec) / 1000);
+
+	return EXIT_SUCCESS;
+}

tests/run-tests.sh

@@ -2,5 +2,12 @@
 
 echo "a" > /tmp/a
 echo "b" > /tmp/b
+echo "c" > /tmp/c
 gcc tests/tests_general.c -o tests_general
 COPYCAT="/tmp/a /tmp/b" build/copycat -- ./tests_general
+
+gcc -lm tests/benchmark.c -o benchmark
+echo -e "\nRunning benchmark without interception:"
+./benchmark
+echo -e "\nRunning benchmark with interception:"
+COPYCAT="/tmp/a /tmp/b" build/copycat -- ./benchmark

tests/tests_general.c

@@ -10,14 +10,18 @@
 
 void check_correct_fd(int fd) {
 	static char c;
+
 	// we should be able to read from the file descriptor
-	assert(read(fd, &c, 1));
+	ssize_t r = read(fd, &c, 1);
+	assert(r);
+
 	// the read char should be 'b', and not 'a'
 	assert(c != 'a');
 	assert(c == 'b');
 
 	// close the descriptor again
-	assert(!close(fd));
+	int a = close(fd);
+	assert(!a);
 }
 
 int do_open(const char *filename) {