Re: [PATCH v8 4/5] iio: osf: add authenticated stream parser

On Thu, 20 Aug 2026 14:06:07 +0900
Jinseob Kim <[email protected]> wrote:

> Add a UART byte-stream parser for Open Sensor Fusion frames.
> 
> The parser searches for the OSF0 wire magic, keeps partial frames
> buffered, checks header length and payload bounds, and passes complete
> candidate frames to a registered frame callback.
> 
> Candidates rejected before authentication drop only the current head
> byte before resynchronizing, so a corrupted unauthenticated payload length
> cannot make the parser skip later valid frames. CRC-valid authenticated
> frames are consumed in full and classified as handled, ignored, or
> rejected.
> 
> Use a direct callback member with an opaque context and keep explicit
> statistics for authenticated outcomes and framing failures.
> 
> Signed-off-by: Jinseob Kim <[email protected]>

One really trivial thing inline.  Please check to see if other areas
of code alignment would benefit from a bit of a reorg.

> diff --git a/drivers/iio/opensensorfusion/osf_stream.c b/drivers/iio/opensensorfusion/osf_stream.c
> new file mode 100644
> index 000000000000..7ce45e631648
> --- /dev/null
> +++ b/drivers/iio/opensensorfusion/osf_stream.c
...

> +
> +static int osf_stream_process(struct osf_stream *stream)
> +{
> +	size_t discarded;
> +	size_t frame_len;
> +	u32 payload_len;
> +	int frame_result;
> +	int first_err = 0;
> +
> +	while (stream->len) {
> +		discarded = osf_stream_discard_to_magic(stream);
> +		if (discarded) {
> +			stream->stats.bad_magic_resyncs++;
> +			stream->stats.dropped_bytes += discarded;
> +			if (!first_err)
> +				first_err = -EPROTO;
> +		}
> +
> +		if (!stream->len)
> +			break;
> +
> +		if (stream->len < OSF_FRAME_HEADER_LEN)
> +			break;
> +
> +		if (get_unaligned_le16(stream->buf + 6) != OSF_FRAME_HEADER_LEN) {
> +			stream->stats.dropped_bytes++;
> +			osf_stream_drop_invalid_head(stream);
> +			if (!first_err)
> +				first_err = -EPROTO;
> +			continue;
> +		}
> +
> +		payload_len = get_unaligned_le32(stream->buf + 10);
> +		if (payload_len > OSF_STREAM_MAX_PAYLOAD_LEN) {
> +			stream->stats.dropped_bytes++;
> +			osf_stream_drop_invalid_head(stream);
> +			if (!first_err)
> +				first_err = -EMSGSIZE;
> +			continue;
> +		}
> +
> +		frame_len = OSF_FRAME_HEADER_LEN + payload_len + OSF_FRAME_CRC_LEN;
> +		if (stream->len < frame_len)
> +			break;
> +
> +		frame_result = stream->receive_frame(stream->frame_context,
> +					     stream->buf, frame_len);

Align after (

> +		if (frame_result < 0) {
> +			if (frame_result == -EBADMSG)
> +				stream->stats.bad_crc_frames++;
> +
> +			/*
> +			 * Decoding failed before the frame was authenticated;
> +			 * payload_len is still untrusted. Drop only the current
> +			 * head and resynchronize.
> +			 */
> +			stream->stats.dropped_bytes++;
> +			osf_stream_drop_invalid_head(stream);
> +			if (!first_err)
> +				first_err = frame_result;
> +			continue;
> +		}
> +
> +		/* Count exactly one outcome for every authenticated frame. */
> +		stream->stats.authenticated_frames++;
> +		switch (frame_result) {
> +		case OSF_STREAM_FRAME_HANDLED:
> +			stream->stats.handled_frames++;
> +			break;
> +		case OSF_STREAM_FRAME_IGNORED:
> +			stream->stats.ignored_frames++;
> +			break;
> +		case OSF_STREAM_FRAME_REJECTED:
> +			stream->stats.rejected_frames++;
> +			break;
> +		default:
> +			/*
> +			 * Preserve the authenticated boundary without scanning the
> +			 * payload for another magic value.
> +			 */
> +			stream->stats.rejected_frames++;
> +			if (!first_err)
> +				first_err = -EPROTO;
> +			break;
> +		}
> +		osf_stream_discard(stream, frame_len);
> +	}
> +
> +	return first_err;
> +}