Re: [PATCH 1/7] syscalls/fanotify20: Introduce helpers for FAN_FS_ERROR test

fanotify20 is a new test validating the FAN_FS_ERROR file system error
event.  This adds some basic structure for the next patches.

The strategy for error reporting testing in fanotify20 goes like this:

  - Generate a broken filesystem
  - Start FAN_FS_ERROR monitoring group
  - Make the file system  notice the error through ordinary operations
  - Observe the event generated

Signed-off-by: Gabriel Krisman Bertazi <redacted>
---
 testcases/kernel/syscalls/fanotify/.gitignore |   1 +
 .../kernel/syscalls/fanotify/fanotify20.c     | 135 ++++++++++++++++++
 2 files changed, 136 insertions(+)
 create mode 100644 testcases/kernel/syscalls/fanotify/fanotify20.c

diff --git a/testcases/kernel/syscalls/fanotify/.gitignore b/testcases/kernel/syscalls/fanotify/.gitignore
index 9554b16b196e..c99e6fff76d6 100644
--- a/testcases/kernel/syscalls/fanotify/.gitignore
+++ b/testcases/kernel/syscalls/fanotify/.gitignore

@@ -17,4 +17,5 @@
 /fanotify17
 /fanotify18
 /fanotify19
+/fanotify20
 /fanotify_child

diff --git a/testcases/kernel/syscalls/fanotify/fanotify20.c b/testcases/kernel/syscalls/fanotify/fanotify20.c
new file mode 100644
index 000000000000..50531bd99cc9
--- /dev/null
+++ b/testcases/kernel/syscalls/fanotify/fanotify20.c

@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2021 Collabora Ltd.
+ *
+ * Author: Gabriel Krisman Bertazi <gabriel@krisman.be>
+ * Based on previous work by Amir Goldstein <amir73il@gmail.com>
+ */
+
+/*\
+ * [Description]
+ * Check fanotify FAN_ERROR_FS events triggered by intentionally
+ * corrupted filesystems:
+ *
+ * - Generate a broken filesystem
+ * - Start FAN_FS_ERROR monitoring group
+ * - Make the file system notice the error through ordinary operations
+ * - Observe the event generated
+ */
+
+#define _GNU_SOURCE
+#include "config.h"
+
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/syscall.h>
+#include "tst_test.h"
+#include <sys/fanotify.h>
+#include <sys/types.h>
+#include <fcntl.h>
+
+#ifdef HAVE_SYS_FANOTIFY_H
+#include "fanotify.h"
+
+#ifndef FAN_FS_ERROR
+#define FAN_FS_ERROR           0x00008000
+#endif
+
+#define BUF_SIZE 256
+static char event_buf[BUF_SIZE];
+int fd_notify;
+
+#define MOUNT_PATH "test_mnt"
+
+static const struct test_case {
+       char *name;
+       void (*trigger_error)(void);
+       void (*prepare_fs)(void);
+} testcases[] = {
+};
+
+int check_error_event_metadata(struct fanotify_event_metadata *event)
+{
+       int fail = 0;
+
+       if (event->mask != FAN_FS_ERROR) {
+               fail++;
+               tst_res(TFAIL, "got unexpected event %llx",
+                       (unsigned long long)event->mask);
+       }
+
+       if (event->fd != FAN_NOFD) {
+               fail++;
+               tst_res(TFAIL, "Weird FAN_FD %llx",
+                       (unsigned long long)event->mask);
+       }
+       return fail;
+}
+
+void check_event(char *buf, size_t len, const struct test_case *ex)
+{
+       struct fanotify_event_metadata *event =
+               (struct fanotify_event_metadata *) buf;
+
+       if (len < FAN_EVENT_METADATA_LEN)
+               tst_res(TFAIL, "No event metadata found");
+
+       if (check_error_event_metadata(event))
+               return;
+
+       tst_res(TPASS, "Successfully received: %s", ex->name);
+}
+
+static void do_test(unsigned int i)
+{
+       const struct test_case *tcase = &testcases[i];
+       size_t read_len;
+
+       tcase->trigger_error();
+
+       read_len = SAFE_READ(0, fd_notify, event_buf, BUF_SIZE);
+
+       check_event(event_buf, read_len, tcase);
+}
+
+static void setup(void)
+{
+       unsigned long i;
+
+       for (i = 0; i < ARRAY_SIZE(testcases); i++)
+               if (testcases[i].prepare_fs)
+                       testcases[i].prepare_fs();
+