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

[Winkler, Tomas]

> 
> 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@xxxxxxxxx>
> > ---
> > 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).
Once it follow closely after enum definition, second in the next patch the 
Ifdef is removed since we  use the function in debug output and not only in debugfs.

> 
> >   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 ?
Not you are not missing anything, it's just an idiom taken from all my debugfs function with multiline output.
> 
> > +	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.
Correct, I can be fixed.
> 
> > +	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 ?
A function doesn't take responsibility on how it used. 
> 
> > +}
> > +
> > +#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;
> >

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