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

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, May 20, 2026 at 03:37:15PM +0200, Andrey Albershteyn wrote:
> 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 <aalbersh@kernel.org>
> ---
>  src/fs-monitor.c  |  9 ++++++---
>  tests/generic/791 | 10 +++++++++-
>  2 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/src/fs-monitor.c b/src/fs-monitor.c
> index 0cf09677a3ef..28436ec2336f 100644
> --- a/src/fs-monitor.c
> +++ b/src/fs-monitor.c
> @@ -117,6 +117,7 @@ next_event:
>  int main(int argc, char **argv)
>  {
>  	int fd;
> +	int error;
>  
>  	char buffer[BUFSIZ];
>  
> @@ -126,15 +127,17 @@ int main(int argc, char **argv)
>  	}
>  
>  	fd = fanotify_init(FAN_CLASS_NOTIF|FAN_REPORT_FID, O_RDONLY);
> +	error = errno;
>  	if (fd < 0) {
>  		perror("fanotify_init");
> -		errx(1, "fanotify_init");
> +		errx(error, "fanotify_init");
>  	}
>  
>  	if (fanotify_mark(fd, FAN_MARK_ADD|FAN_MARK_FILESYSTEM,
>  			  FAN_FS_ERROR, AT_FDCWD, argv[1])) {
> +		error = errno;
>  		perror("fanotify_mark");
> -		errx(1, "fanotify_mark");
> +		errx(errno, "fanotify_mark");
>  	}
>  
>  	printf("fanotify active\n");
> @@ -144,7 +147,7 @@ int main(int argc, char **argv)
>  		int n = read(fd, buffer, BUFSIZ);
>  
>  		if (n < 0)
> -			errx(1, "read");
> +			errx(errno, "read");
>  
>  		handle_notifications(buffer, n);
>  	}
> diff --git a/tests/generic/791 b/tests/generic/791
> index 90242292cba2..1d3a6c181011 100755
> --- a/tests/generic/791
> +++ b/tests/generic/791
> @@ -123,10 +123,18 @@ fi
>  _dmerror_unmount
>  _dmerror_mount
>  
> -$here/src/fs-monitor $SCRATCH_MNT > $tmp.fsmonitor &
> +$here/src/fs-monitor $SCRATCH_MNT > $tmp.fsmonitor 2>&1 &
>  fsmonitor_pid=$!
>  sleep 1
>  
> +if ! kill -0 $fsmonitor_pid 2>/dev/null; then
> +	wait $fsmonitor_pid
> +	# Function not implemented
> +	if [ $? -eq 38 ]; then

error numbers aren't the same across architectures, so you generally
have to strerror/perror and grep for that in the output.

Alternately we could add a getopt loop to main() so that you could pass
in a --check that would do the setup and exit(0) just before the while
loop; and then you could add:

$here/src/fs-monitor $SCRATCH_MNT --check &> /dev/null || \
	_notrun "fanotify too old"

--D

> +		_notrun "Kernel doesn't support fanotify"
> +	fi
> +fi
> +
>  _dmerror_mark_range_bad $bad_sector $bad_len
>  
>  cat >> $seqres.full << ENDL
> -- 
> 2.51.2
>