linux-kernel - Re: [PATCH] bcachefs: chardev: make bch_chardev

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Message-ID: <sky4no6qxoytrkd3azcf5hokmhxrrpluao5ilhbqvprqxwuj4r@ozwmbbulfbrt>
Date: Wed, 6 Mar 2024 08:50:04 -0300
From: "Ricardo B. Marliere" <ricardo@...liere.net>
To: Hongbo Li <lihongbo22@...wei.com>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>, 
	Brian Foster <bfoster@...hat.com>, linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] bcachefs: chardev: make bch_chardev_class constant

On  6 Mar 09:23, Hongbo Li wrote:
> On 2024/3/6 4:21, Ricardo B. Marliere wrote:
> > Since commit 43a7206b0963 ("driver core: class: make class_register() take
> > a const *"), the driver core allows for struct class to be in read-only
> > memory, so move the bch_chardev_class structure to be declared at build
> > time placing it into read-only memory, instead of having to be dynamically
> > allocated at boot time.
> > 
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Suggested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Signed-off-by: Ricardo B. Marliere <ricardo@...liere.net>
> > ---
> >   fs/bcachefs/chardev.c | 23 ++++++++++++-----------
> >   1 file changed, 12 insertions(+), 11 deletions(-)
> > 
> > diff --git a/fs/bcachefs/chardev.c b/fs/bcachefs/chardev.c
> > index 226b39c17667..af587453fd3d 100644
> > --- a/fs/bcachefs/chardev.c
> > +++ b/fs/bcachefs/chardev.c
> > @@ -940,7 +940,9 @@ static const struct file_operations bch_chardev_fops = {
> >   };
> >   
> >   static int bch_chardev_major;
> > -static struct class *bch_chardev_class;
> > +static const struct class bch_chardev_class = {
> > +	.name = "bcachefs",
> > +};
> >   static struct device *bch_chardev;
> >   
> >   void bch2_fs_chardev_exit(struct bch_fs *c)
> > @@ -957,7 +959,7 @@ int bch2_fs_chardev_init(struct bch_fs *c)
> >   	if (c->minor < 0)
> >   		return c->minor;
> >   
> > -	c->chardev = device_create(bch_chardev_class, NULL,
> > +	c->chardev = device_create(&bch_chardev_class, NULL,
> >   				   MKDEV(bch_chardev_major, c->minor), c,
> >   				   "bcachefs%u-ctl", c->minor);
> >   	if (IS_ERR(c->chardev))
> > @@ -968,26 +970,25 @@ int bch2_fs_chardev_init(struct bch_fs *c)
> >   
> >   void bch2_chardev_exit(void)
> >   {
> > -	if (!IS_ERR_OR_NULL(bch_chardev_class))
> > -		device_destroy(bch_chardev_class,
> > -			       MKDEV(bch_chardev_major, U8_MAX));
> > -	if (!IS_ERR_OR_NULL(bch_chardev_class))
> > -		class_destroy(bch_chardev_class);
> > +	device_destroy(&bch_chardev_class, MKDEV(bch_chardev_major, U8_MAX));
> > +	class_unregister(&bch_chardev_class);
> >   	if (bch_chardev_major > 0)
> >   		unregister_chrdev(bch_chardev_major, "bcachefs");
> >   }
> >   
> >   int __init bch2_chardev_init(void)
> >   {
> > +	int ret;
> > +
> >   	bch_chardev_major = register_chrdev(0, "bcachefs-ctl", &bch_chardev_fops);
> >   	if (bch_chardev_major < 0)
> >   		return bch_chardev_major;
> >   
> > -	bch_chardev_class = class_create("bcachefs");
> > -	if (IS_ERR(bch_chardev_class))
> > -		return PTR_ERR(bch_chardev_class);
> > +	ret = class_register(&bch_chardev_class);
> > +	if (ret)
> Here, I think you should call class_unregister to relase resource which 
> allocated before. And the same thing shoud be done in other exception exit.

Hi Hongbo,

Thank you for the feedback. Did you mean that bch_chardev_major should
be unregistered if the class_register() call fails? Because if it does,
there is no need to call class_unregister().

> > +		return ret;
> >   
> > -	bch_chardev = device_create(bch_chardev_class, NULL,
> > +	bch_chardev = device_create(&bch_chardev_class, NULL,
> >   				    MKDEV(bch_chardev_major, U8_MAX),
> >   				    NULL, "bcachefs-ctl");
> >   	if (IS_ERR(bch_chardev))
> like here..

Can you please elaborate?

Best regards,
-	Ricardo.


> > 
> > ---
> > base-commit: 90d35da658da8cff0d4ecbb5113f5fac9d00eb72
> > change-id: 20240305-bcachefs-27a4bb8b9f4f
> > 
> > Best regards,