From 1f5069d13f1259d98d837c1c9bdc49fb9fe8b984 Mon Sep 17 00:00:00 2001
From: Yauhen Kharuzhy <jekhor@gmail.com>
Date: Mon, 1 Jan 2024 23:17:01 +0200
Subject: [PATCH] iio-buffer-utils: Correctly disable sensors when exiting

The enable_sensors() function has an error preventing sensor
disabling: it checks if the sensor is already enabled and does nothing
even if we need to disable it.

Also, there is lack of error handling in the _write_sysfs_int()
function: the result of fprintf() is not checked. If some error occurs
during writing to the sysfs attribute, it is ignored.

Fix these errors and change the order of sysfs attribute writing during
device releasing to avoid "Device or resource busy" errors (a buffer
should be disabled before scan elements).
---
 src/iio-buffer-utils.c | 51 ++++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/src/iio-buffer-utils.c b/src/iio-buffer-utils.c
index 597e550..d0939d3 100644
--- a/src/iio-buffer-utils.c
+++ b/src/iio-buffer-utils.c
@@ -356,27 +356,38 @@ _write_sysfs_int (const char *filename,
 	int ret = 0;
 	g_autoptr(FILE) sysfsfp = NULL;
 	int test;
-	char *temp;
+	g_autofree char *temp = NULL;
+
 	temp = g_build_filename (basedir, filename, NULL);
 	sysfsfp = fopen(temp, "w");
 	if (sysfsfp == NULL) {
 		g_warning ("Could not open for write '%s'", temp);
-		ret = -errno;
-		goto error_free;
+		return -errno;
 	}
+
+	setvbuf(sysfsfp, NULL, _IONBF, 0);
+
 	if (type)
-		fprintf(sysfsfp, "%d %d", val, val2);
+		ret = fprintf(sysfsfp, "%d %d", val, val2);
 	else
-		fprintf(sysfsfp, "%d", val);
+		ret = fprintf(sysfsfp, "%d", val);
+
 	g_clear_pointer (&sysfsfp, fclose);
 
+	if (ret < 0) {
+		g_warning ("Could not write to '%s': %s", temp, g_strerror(-ret));
+		return ret;
+	}
+
+	ret = 0;
+
 	if (verify) {
 		sysfsfp = fopen(temp, "r");
 		if (sysfsfp == NULL) {
 			g_warning ("Could not open for read '%s'", temp);
-			ret = -errno;
-			goto error_free;
+			return -errno;
 		}
+
 		if (fscanf(sysfsfp, "%d", &test) != 1 ||
 		    test != val) {
 			g_warning ("Possible failure in int write %d to %s",
@@ -384,8 +395,7 @@ _write_sysfs_int (const char *filename,
 			ret = -1;
 		}
 	}
-error_free:
-	g_free (temp);
+
 	return ret;
 }
 
@@ -673,6 +683,9 @@ enable_sensors (GUdevDevice *dev,
 	gboolean ret = FALSE;
 	g_autoptr(GError) error = NULL;
 
+	g_debug ("%s sensors for device '%s'", enable ? "Enabling" : "Disabling",
+		 g_udev_device_get_sysfs_path (dev));
+
 	device_dir = g_build_filename (g_udev_device_get_sysfs_path (dev), "scan_elements", NULL);
 	dir = g_dir_open (device_dir, 0, &error);
 	if (!dir) {
@@ -689,7 +702,7 @@ enable_sensors (GUdevDevice *dev,
 
 		/* Already enabled? */
 		path = g_strdup_printf ("scan_elements/%s", name);
-		if (g_udev_device_get_sysfs_attr_as_boolean (dev, path)) {
+		if (enable && g_udev_device_get_sysfs_attr_as_boolean (dev, path)) {
 			g_debug ("Already enabled sensor %s/%s", device_dir, name);
 			ret = TRUE;
 			g_free (path);
@@ -699,18 +712,21 @@ enable_sensors (GUdevDevice *dev,
 
 		/* Enable */
 		if (write_sysfs_int (name, device_dir, enable) < 0) {
-			g_warning ("Could not enable sensor %s/%s", device_dir, name);
+			g_warning ("Could not write %d to %s/%s",
+				   enable, device_dir, name);
 			continue;
 		}
 
 		ret = TRUE;
-		g_debug ("Enabled sensor %s/%s", device_dir, name);
+		g_debug ("%s sensor %s/%s", enable ? "Enabled" : "Disabled",
+			 device_dir, name);
 	}
 	g_dir_close (dir);
 	g_free (device_dir);
 
 	if (!ret) {
-		g_warning ("Failed to enable any sensors for device '%s'",
+		g_warning ("Failed to %s any sensors for device '%s'",
+			   enable ? "enable" : "disable",
 			   g_udev_device_get_sysfs_path (dev));
 	}
 
@@ -785,13 +801,14 @@ buffer_drv_data_free (BufferDrvData *buffer_data)
 	if (buffer_data == NULL)
 		return;
 
+	/* A buffer should be disabled before scan elements to avoid a
+	 * "Device or resource busy" error */
+	disable_ring_buffer (buffer_data);
+	g_free (buffer_data->trigger_name);
+
 	enable_sensors (buffer_data->device, 0);
 	g_clear_object (&buffer_data->device);
 
-	disable_ring_buffer (buffer_data);
-
-	g_free (buffer_data->trigger_name);
-
 	for (i = 0; i < buffer_data->channels_count; i++)
 		channel_info_free (buffer_data->channels[i]);
 	g_free (buffer_data->channels);