contrib: add getdents_c

Same thing like contrib/getdents, but written in C.

contrib/getdents/.gitignore

@@ -0,0 +1 @@
+/getdents

contrib/getdents_c/.gitignore

@@ -0,0 +1 @@
+/getdents_c

contrib/getdents_c/Makefile

@@ -0,0 +1,2 @@
+getdents_c: *.c Makefile
+	gcc getdents.c -o getdents_c

contrib/getdents_c/getdents.c

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+// See ../getdents/getdents.go for some info on why
+// this exists.
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <errno.h>
+
+int main(int argc, char *argv[])
+{
+    if(argc < 2) {
+        printf("Usage: %s PATH\n", argv[0]);
+        printf("Run getdents(2) on PATH\n");
+        exit(1);
+    }
+
+    const char *path = argv[1];
+    int fd = open(path, O_RDONLY);
+    if (fd == -1) {
+        perror("open");
+        exit(1);
+    }
+
+    char tmp[10000];
+    int sum = 0;
+    for ( ; ; ) {
+        int n = syscall(SYS_getdents64, fd, tmp, sizeof(tmp));
+        printf("getdents64 fd%d: n=%d, errno=%d\n", fd, n, errno);
+        if (n <= 0) {
+            printf("total %d bytes\n", sum);
+            break;
+        }
+        sum += n;
+    }
+}