linux-kernel - Re: [PATCH v2 2/3] staging: rtl8192u: move debug files to debugfs

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Date:   Tue, 19 Jul 2022 23:30:48 -0700
From:   Tong Zhang <ztong0001@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Colin Ian King <colin.king@...el.com>,
        Saurav Girepunje <saurav.girepunje@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-staging@...ts.linux.dev,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH v2 2/3] staging: rtl8192u: move debug files to debugfs

On Tue, Jul 19, 2022 at 5:53 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Jul 18, 2022 at 10:50:37PM -0700, Tong Zhang wrote:
> > There are 4 debug files created under /proc/net/[Devname]. Devname could
> > Due to this is purely for debuging as files are created read only,
> > move this to debugfs like other NIC drivers do instead of using procfs.
> > This is also to prepare for address rmmod warn issue.
>
> Minor comments based on good debugfs usage:
>
> > --- a/drivers/staging/rtl8192u/r8192U.h
> > +++ b/drivers/staging/rtl8192u/r8192U.h
> > @@ -1061,6 +1061,9 @@ typedef struct r8192_priv {
> >       struct delayed_work gpio_change_rf_wq;
> >       struct delayed_work initialgain_operate_wq;
> >       struct workqueue_struct *priv_wq;
> > +
> > +     /* debugfs */
> > +     struct dentry *debugfs_dir;
>
> Why do you need to save this dentry?  Can't you just look it up when you
> want to remove the files?
>
> > +void rtl8192_debugfs_init(struct net_device *dev)
> >  {
> > -     struct proc_dir_entry *dir;
> > +     struct dentry *dir;
> > +     struct r8192_priv *priv = (struct r8192_priv *)ieee80211_priv(dev);
>
> No need to cast this.  Same for later on in this file.
>
> > -     if (!rtl8192_proc)
> > +     dir = debugfs_create_dir(dev->name, NULL);
> > +     if (IS_ERR(dir))
> >               return;
>

I'm reading this code and your comment again.
Adding this check will avoid calling into debugfs_create_file() and 4
function calls and doing checks from there, probably will save a
couple of CPU cycles and avoid branch prediction penalty if there is
any.
I don't think the compiler can optimize for this case though it's not
performance critical. Anyho I personally feel it is better to keep
this.

> No need to check, just keep moving on.
>
> >
> > -     dir = proc_mkdir_data(dev->name, 0, rtl8192_proc, dev);
> > -     if (!dir)
> > -             return;
> > +     debugfs_create_file("stats-rx", 0444, dir, dev, &rtl8192_usb_stats_rx_fops);
> > +     debugfs_create_file("stats-tx", 0444, dir, dev, &rtl8192_usb_stats_tx_fops);
> > +     debugfs_create_file("stats-ap", 0444, dir, dev, &rtl8192_usb_stats_ap_fops);
> > +     debugfs_create_file("registers", 0444, dir, dev, &rtl8192_usb_registers_fops);
> >
> > -     proc_create_single("stats-rx", S_IFREG | 0444, dir,
> > -                        proc_get_stats_rx);
> > -     proc_create_single("stats-tx", S_IFREG | 0444, dir,
> > -                        proc_get_stats_tx);
> > -     proc_create_single("stats-ap", S_IFREG | 0444, dir,
> > -                        proc_get_stats_ap);
> > -     proc_create_single("registers", S_IFREG | 0444, dir,
> > -                        proc_get_registers);
> > +     priv->debugfs_dir = dir;

Please correct me if I am wrong (yes probably).
As I mentioned in another email, I am not sure if there is another way
to look up the old entry so I'm saving the old entry here.
I cheated a little bit by using similar routine as in

net/mac80211/debugfs_netdev.c:865 void
ieee80211_debugfs_rename_netdev(struct ieee80211_sub_if_data *sdata)
drivers/net/ethernet/amd/xgbe/xgbe-debugfs.c: 520 void
xgbe_debugfs_rename(struct xgbe_prv_data *pdata)

>
> Again, no need to save this, just look it up when removing the
> directory.
>
> thanks,
>
> greg k-h


Thanks and have a good one!
- Tong