[RFC PATCH] usb: common: change usb_debug_root as static variable

[RFC PATCH] usb: common: change usb_debug_root as static variable

[Chunfeng Yun]

Try to avoid using extern global variable, and provide two
functions for the usage cases

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.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;
+
+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);
+}
+EXPORT_SYMBOL_GPL(usb_debugfs_create_file);
 
 static int __init usb_common_init(void)
 {
diff --git a/include/linux/usb.h b/include/linux/usb.h
index e656e7b4b1e4..ad96e0aa0127 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -2001,7 +2001,10 @@ extern void usb_register_notify(struct notifier_block *nb);
 extern void usb_unregister_notify(struct notifier_block *nb);
 
 /* debugfs stuff */
-extern struct dentry *usb_debug_root;
+extern struct dentry *usb_debugfs_create_dir(const char *name);
+extern struct dentry *
+usb_debugfs_create_file(const char *name, umode_t mode, void *data,
+			const struct file_operations *fops);
 
 /* LED triggers */
 enum usb_led_event {
-- 
2.23.0

Re: [RFC PATCH] usb: common: change usb_debug_root as static variable

[Greg Kroah-Hartman]

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?

> Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.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?  You can't do that in a single patch
either :(

> +
> +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.

thanks,

greg k-h

Re: [RFC PATCH] usb: common: change usb_debug_root as static variable

[Chunfeng Yun]

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@mediatek.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