[PATCH v2] generic/791: don't run if kernel misses FANOTIFY

If FANOTIFY=no in the kernel, then fs-monitor will fail to start. Fix
fs-monitor error codes to detect and skip the test on "Function not
implemented" code.

Signed-off-by: Andrey Albershteyn <[email protected]>
---
Changes from v1:
- Remove returning of errno
- Instead of checking for error code add new -c argument to fs-monitor

---
 src/fs-monitor.c  | 19 ++++++++++++++++++-
 tests/generic/791 |  3 +++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/fs-monitor.c b/src/fs-monitor.c
index 0cf09677a3ef..dd91a5d7f623 100644
--- a/src/fs-monitor.c
+++ b/src/fs-monitor.c
@@ -117,6 +117,8 @@ next_event:
 int main(int argc, char **argv)
 {
 	int fd;
+	int opt;
+	int check = 0;
 
 	char buffer[BUFSIZ];
 
@@ -125,14 +127,29 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	while ((opt = getopt(argc, argv, "c")) != -1) {
+		switch (opt) {
+		case 'c':
+			check = 1;
+			break;
+		default:
+			fprintf(stderr, "Usage: %s [-c] path\n",
+				argv[0]);
+			exit(EXIT_FAILURE);
+		}
+	}
+
 	fd = fanotify_init(FAN_CLASS_NOTIF|FAN_REPORT_FID, O_RDONLY);
+	if (check)
+		exit(fd < 0);
+
 	if (fd < 0) {
 		perror("fanotify_init");
 		errx(1, "fanotify_init");
 	}
 
 	if (fanotify_mark(fd, FAN_MARK_ADD|FAN_MARK_FILESYSTEM,
-			  FAN_FS_ERROR, AT_FDCWD, argv[1])) {
+			  FAN_FS_ERROR, AT_FDCWD, argv[optind])) {
 		perror("fanotify_mark");
 		errx(1, "fanotify_mark");
 	}
diff --git a/tests/generic/791 b/tests/generic/791
index 90242292cba2..edefbb7767c3 100755
--- a/tests/generic/791
+++ b/tests/generic/791
@@ -65,6 +65,9 @@ _dmerror_mount >> $seqres.full 2>&1
 
 test $FSTYP = xfs && _xfs_force_bdev data $SCRATCH_MNT
 
+$here/src/fs-monitor -c $SCRATCH_MNT &> /dev/null || \
+		_notrun "fanotify too old"
+
 # Write a file with 4 file blocks worth of data, figure out the LBA to target
 victim=$SCRATCH_MNT/a
 file_blksz=$(_get_file_block_size $SCRATCH_MNT)
-- 
2.51.2