1 files changed, 67 insertions, 0 deletions
diff --git a/tests/fcntl_locker.c b/tests/fcntl_locker.c
new file mode 100644
index 0000000..fa2e9dc
--- /dev/null
+++ b/tests/fcntl_locker.c
@@ -0,0 +1,67 @@
+// Takes two files and exits with 0 if fcntl-locking one fcntl-locks the other.
+// If the files don't fcntl-lock each other, returns 1.
+// If any other error occurs, returns 2.
+
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+int main(int argc, const char* argv[]) {
+    if (argc != 3) {
+        fprintf(stderr, "expecting exactly two arguments\n");
+        return 2;
+    }
+
+    int fd1 = -1;
+    int fd2 = -1;
+    int result = 2;
+
+    fd1 = open(argv[1], O_RDWR);
+    if (fd1 == -1) {
+        perror("failed to open the first file");
+        goto exit;
+    }
+    fd2 = open(argv[2], O_RDWR);
+    if (fd2 == -1) {
+        perror("failed to open the second file");
+        goto exit;
+    }
+
+    struct flock lock;
+    memset(&lock, 0, sizeof(lock));
+    lock.l_type = F_WRLCK;
+    lock.l_whence = SEEK_SET;
+    lock.l_start = 0;
+    lock.l_len = 0;
+    if (fcntl(fd1, F_SETLK, &lock) == -1) {
+        perror("fcntl F_SETLK on the first file failed");
+        goto exit;
+    }
+
+    memset(&lock, 0, sizeof(lock));
+    lock.l_type = F_WRLCK;
+    lock.l_whence = SEEK_SET;
+    lock.l_start = 0;
+    lock.l_len = 0;
+    if (fcntl(fd2, F_SETLK, &lock) == -1) {
+        if (errno == EACCES || errno == EAGAIN) {
+            result = 0;
+            goto exit;
+        } else {
+            perror("fcntl F_SETLK on the second file failed");
+            goto exit;
+        }
+    } else {
+        result = 1;
+        goto exit;
+    }
+
+exit:
+    close(fd1);
+    close(fd2);
+    return result;
+}