iiod: Update read_line() to work with UART

Previously, in the non-socket case, read_line() would read as much data
as possible in one read() call. As it was used almost exclusively for
USB, the amount of data returned always corresponded to the size of the bulk
data sent by the client, aka. a full line and nothing more.

With UART though, if we try reading as much data as possible, we might
get just that, and end up reading much more data than we need,
disrupting the protocol.

Fix this by reading character by character until the \n is found in the
non-socket, non-USB case.

Signed-off-by: Paul Cercueil <[email protected]>

iiod/ops.c

@@ -1397,12 +1397,12 @@ int set_buffers_count(struct parser_pdata *pdata,
 
 ssize_t read_line(struct parser_pdata *pdata, char *buf, size_t len)
 {
+	size_t bytes_read = 0;
 	ssize_t ret;
+	bool found;
 
 	if (pdata->fd_in_is_socket) {
 		struct pollfd pfd[2];
-		bool found;
-		size_t bytes_read = 0;
 
 		pfd[0].fd = pdata->fd_in;
 		pfd[0].events = POLLIN | POLLRDHUP;
@@ -1445,16 +1445,34 @@ ssize_t read_line(struct parser_pdata *pdata, char *buf, size_t len)
 
 			bytes_read += to_trunc;
 		} while (!found && len);
+	} else if (pdata->is_usb) {
+		ret = pdata->readfd(pdata, buf, len);
 
-		/* No \n found? Just garbage data */
-		if (!found)
-			ret = -EIO;
-		else
-			ret = bytes_read;
+		found = buf[ret - 1] == '\n';
 	} else {
-		ret = pdata->readfd(pdata, buf, len);
+		while (len) {
+			ret = pdata->readfd(pdata, buf, 1);
+			if (ret < 0)
+			      return ret;
+
+			bytes_read++;
+
+			if (*buf == '\n')
+			      break;
+
+			len--;
+			buf++;
+		}
+
+		found = !!len;
 	}
 
+	/* No \n found? Just garbage data */
+	if (!found)
+		ret = -EIO;
+	else
+		ret = bytes_read;
+
 	return ret;
 }