linux-kernel - Re: [RFC PATCH] usb: common: change usb_debug

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Message-ID: <1572921077.18464.55.camel@mhfsdcap03>
Date:   Tue, 5 Nov 2019 10:31:17 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Fabrizio Castro <fabrizio.castro@...renesas.com>,
        <linux-usb@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] usb: common: change usb_debug_root as static
 variable

On Fri, 2019-11-01 at 10:02 +0100, Greg Kroah-Hartman wrote:
> On Fri, Nov 01, 2019 at 10:29:09AM +0800, Chunfeng Yun wrote:
> > Try to avoid using extern global variable, and provide two
> > functions for the usage cases
> 
> That is 3 different things all in one patch, not generally considered a
> good thing at all.

> 
> Also, who is going to use these new functions?  Why are they needed?
After remove global variable usb_debug_root, the drivers using
usb_debug_root to create directory or files will use these new APIs
instead.

> 
> > Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> > ---
> > NOTE:
> >     Prepared but not send out patches for drivers using usb_debug_root,
> > because I'm not sure whether this patch is needed, and many drivers
> > will be modified.
> > ---
> >  drivers/usb/common/common.c | 16 ++++++++++++++--
> >  include/linux/usb.h         |  5 ++++-
> >  2 files changed, 18 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/usb/common/common.c b/drivers/usb/common/common.c
> > index 1433260d99b4..639ee6d243a2 100644
> > --- a/drivers/usb/common/common.c
> > +++ b/drivers/usb/common/common.c
> > @@ -293,8 +293,20 @@ struct device *usb_of_get_companion_dev(struct device *dev)
> >  EXPORT_SYMBOL_GPL(usb_of_get_companion_dev);
> >  #endif
> >  
> > -struct dentry *usb_debug_root;
> > -EXPORT_SYMBOL_GPL(usb_debug_root);
> > +static struct dentry *usb_debug_root;
> 
> Doesn't this break things as-is? 
Yes, it will, I didn't send out other patches for the drivers using
usb_debug_root.

>  You can't do that in a single patch
> either :(
When I make usb_debug_root as static variable, two APIs need be added
due to other driver use it to create directory or file.

> 
> > +
> > +struct dentry *usb_debugfs_create_dir(const char *name)
> > +{
> > +	return debugfs_create_dir(name, usb_debug_root);
> > +}
> > +EXPORT_SYMBOL_GPL(usb_debugfs_create_dir);
> > +
> > +struct dentry *usb_debugfs_create_file(const char *name, umode_t mode,
> > +			void *data, const struct file_operations *fops)
> > +{
> > +	return debugfs_create_file(name, mode, usb_debug_root, data, fops);
> 
> I doubt many people want to create a file in the usb "root" debugfs
> directory, right?  They _should_ be just creating a new subdirectory in
> there instead.
Currently only three .c files creates a file under usb 'root' debugfs
directory.

> 
> thanks,
> 
> greg k-h