Re: [char-misc-next v3 4/8] watchdog: mei_wdt: add status debugfs entry

[Guenter Roeck <linux@roeck-us.net>]

On 12/21/2015 03:17 PM, Tomas Winkler wrote:
> Add entry for dumping current watchdog internal state
>
> Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
> ---
> V2: new in the series
> V3: rebase
>   drivers/watchdog/mei_wdt.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 88 insertions(+)
>
> diff --git a/drivers/watchdog/mei_wdt.c b/drivers/watchdog/mei_wdt.c
> index 5b28a1e95ac1..ab9aec218d69 100644
> --- a/drivers/watchdog/mei_wdt.c
> +++ b/drivers/watchdog/mei_wdt.c
> @@ -15,6 +15,7 @@
>   #include <linux/module.h>
>   #include <linux/slab.h>
>   #include <linux/interrupt.h>
> +#include <linux/debugfs.h>
>   #include <linux/watchdog.h>
>
>   #include <linux/uuid.h>
> @@ -54,6 +55,24 @@ enum mei_wdt_state {
>   	MEI_WDT_STOPPING,
>   };
>
> +#if IS_ENABLED(CONFIG_DEBUG_FS)
> +static const char *mei_wdt_state_str(enum mei_wdt_state state)
> +{
> +	switch (state) {
> +	case MEI_WDT_IDLE:
> +		return "IDLE";
> +	case MEI_WDT_START:
> +		return "START";
> +	case MEI_WDT_RUNNING:
> +		return "RUNNING";
> +	case MEI_WDT_STOPPING:
> +		return "STOPPING";
> +	default:
> +		return "unknown";
> +	}
> +}
> +#endif /* CONFIG_DEBUG_FS */
> +
I still don't understand why this code has to be here instead of
further below (at <----> mark).

>   struct mei_wdt;
>
>   /**
> @@ -76,6 +95,8 @@ struct mei_wdt_dev {
>    * @cldev: mei watchdog client device
>    * @state: watchdog internal state
>    * @timeout: watchdog current timeout
> + *
> + * @dbgfs_dir: debugfs dir entry
>    */
>   struct mei_wdt {
>   	struct mei_wdt_dev *mwd;
> @@ -83,6 +104,10 @@ struct mei_wdt {
>   	struct mei_cl_device *cldev;
>   	enum mei_wdt_state state;
>   	u16 timeout;
> +
> +#if IS_ENABLED(CONFIG_DEBUG_FS)
> +	struct dentry *dbgfs_dir;
> +#endif /* CONFIG_DEBUG_FS */
>   };
>
>   /*
> @@ -387,6 +412,65 @@ static int mei_wdt_register(struct mei_wdt *wdt)
>   	return 0;
>   }
>
> +#if IS_ENABLED(CONFIG_DEBUG_FS)
> +

<---->

> +static ssize_t mei_dbgfs_read_state(struct file *file, char __user *ubuf,
> +				    size_t cnt, loff_t *ppos)
> +{
> +	struct mei_wdt *wdt = file->private_data;
> +	const size_t bufsz = 32;
> +	char buf[32];
> +	ssize_t pos = 0;
> +
> +	pos += scnprintf(buf + pos, bufsz - pos, "state: %s\n",
> +			 mei_wdt_state_str(wdt->state));
> +
Seems to me that "pos = ..." would accomplish exactly the same
without having to pre-initialize pos. I also don't understand the use of
"+ pos" and "- pos" in the parameter field. pos is 0, isn't it ?
When would it ever be non-0 ?

	pos = scnprintf(buf, sizeof(buf), "state: %s\n", mei_wdt_state_str(wdt->state));

What am I missing here ?

> +	return simple_read_from_buffer(ubuf, cnt, ppos, buf, pos);
> +}
> +
> +static const struct file_operations dbgfs_fops_state = {
> +	.open = simple_open,
> +	.read = mei_dbgfs_read_state,
> +	.llseek = generic_file_llseek,
> +};
> +
> +static void dbgfs_unregister(struct mei_wdt *wdt)
> +{
> +	if (!wdt->dbgfs_dir)
> +		return;
> +	debugfs_remove_recursive(wdt->dbgfs_dir);

debugfs_remove_recursive() checks if the parameter is NULL,
so it is not necessary to check if it is NULL before the call.

> +	wdt->dbgfs_dir = NULL;
> +}
> +
> +static int dbgfs_register(struct mei_wdt *wdt)
> +{
> +	struct dentry *dir, *f;
> +
> +	dir = debugfs_create_dir(KBUILD_MODNAME, NULL);
> +	if (!dir)
> +		return -ENOMEM;
> +
> +	wdt->dbgfs_dir = dir;
> +	f = debugfs_create_file("state", S_IRUSR, dir, wdt, &dbgfs_fops_state);
> +	if (!f)
> +		goto err;
> +
> +	return 0;
> +err:
> +	dbgfs_unregister(wdt);
> +	return -ENODEV;

The error value is ignored by the caller - why bother returning an error in the first place ?

> +}
> +
> +#else
> +
> +static inline void dbgfs_unregister(struct mei_wdt *wdt) {}
> +
> +static inline int dbgfs_register(struct mei_wdt *wdt)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_DEBUG_FS */
> +
>   static int mei_wdt_probe(struct mei_cl_device *cldev,
>   			 const struct mei_cl_device_id *id)
>   {
> @@ -414,6 +498,8 @@ static int mei_wdt_probe(struct mei_cl_device *cldev,
>   	if (ret)
>   		goto err_disable;
>
> +	dbgfs_register(wdt);
> +
>   	return 0;
>
>   err_disable:
> @@ -433,6 +519,8 @@ static int mei_wdt_remove(struct mei_cl_device *cldev)
>
>   	mei_cldev_disable(cldev);
>
> +	dbgfs_unregister(wdt);
> +
>   	kfree(wdt);
>
>   	return 0;
>