On Fri, Jun 25, 2021 at 11:30:19PM -0700, longli@linuxonhyperv.com wrote:

+#ifdef CONFIG_DEBUG_FS
+struct dentry *az_blob_debugfs_root;
+#endif

No need to keep this dentry, just look it up if you need it.

+
+static struct az_blob_device az_blob_dev;
+
+static int az_blob_ringbuffer_size = (128 * 1024);
+module_param(az_blob_ringbuffer_size, int, 0444);
+MODULE_PARM_DESC(az_blob_ringbuffer_size, "Ring buffer size (bytes)");

This is NOT the 1990's, please do not create new module parameters.
Just make this work properly for everyone.

+#define AZ_ERR 0
+#define AZ_WARN 1
+#define AZ_DBG 2
+static int log_level = AZ_ERR;
+module_param(log_level, int, 0644);
+MODULE_PARM_DESC(log_level,
+	"Log level: 0 - Error (default), 1 - Warning, 2 - Debug.");

A single driver does not need a special debug/log level, use the
system-wide functions and all will "just work"

+
+static uint device_queue_depth = 1024;
+module_param(device_queue_depth, uint, 0444);
+MODULE_PARM_DESC(device_queue_depth,
+	"System level max queue depth for this device");
+
+#define az_blob_log(level, fmt, args...)	\
+do {	\
+	if (level <= log_level)	\
+		pr_err("%s:%d " fmt, __func__, __LINE__, ##args);	\
+} while (0)
+
+#define az_blob_dbg(fmt, args...) az_blob_log(AZ_DBG, fmt, ##args)
+#define az_blob_warn(fmt, args...) az_blob_log(AZ_WARN, fmt, ##args)
+#define az_blob_err(fmt, args...) az_blob_log(AZ_ERR, fmt, ##args)

Again, no.

Just use dev_dbg(), dev_warn(), and dev_err() and there is no need for
anything "special".  This is just one tiny driver, do not rewrite logic
like this for no reason.

+static void az_blob_remove_device(struct az_blob_device *dev)
+{
+	wait_event(dev->file_wait, list_empty(&dev->file_list));
+	misc_deregister(&az_blob_misc_device);
+#ifdef CONFIG_DEBUG_FS

No need for the #ifdef.

+	debugfs_remove_recursive(az_blob_debugfs_root);
+#endif
+	/* At this point, we won't get any requests from user-mode */
+}
+
+static int az_blob_create_device(struct az_blob_device *dev)
+{
+	int rc;
+	struct dentry *d;
+
+	rc = misc_register(&az_blob_misc_device);
+	if (rc) {
+		az_blob_err("misc_register failed rc %d\n", rc);
+		return rc;
+	}
+
+#ifdef CONFIG_DEBUG_FS

No need for the #ifdef

+	az_blob_debugfs_root = debugfs_create_dir("az_blob", NULL);
+	if (!IS_ERR_OR_NULL(az_blob_debugfs_root)) {

No need to check this.

+		d = debugfs_create_file("pending_requests", 0400,
+			az_blob_debugfs_root, NULL,
+			&az_blob_debugfs_fops);
+		if (IS_ERR_OR_NULL(d)) {

How can that be NULL?

No need to ever check any debugfs calls, please just make them and move
on.

thanks,

greg k-h