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

[Guenter Roeck]

On 12/23/2015 02:48 PM, Winkler, Tomas wrote:
> > 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.

I don't think that is a good reason for using the more complex code 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.
> 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.

For an exported function I would agree, but not in a static function.

Thanks,
Guenter

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