linux-kernel - Re: [Patch v2 2/3] Drivers: hv: add Azure Blob driver

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Date:   Tue, 29 Jun 2021 08:24:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     longli@...uxonhyperv.com
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        Long Li <longli@...rosoft.com>,
        Jonathan Corbet <corbet@....net>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andra Paraschiv <andraprs@...zon.com>,
        Siddharth Gupta <sidgup@...eaurora.org>,
        Hannes Reinecke <hare@...e.de>, linux-doc@...r.kernel.org
Subject: Re: [Patch v2 2/3] Drivers: hv: add Azure Blob driver

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