Re: [PATCH] bcachefs: chardev: make bch_chardev_class constant

[Hongbo Li]

On 2024/3/6 19:50, Ricardo B. Marliere wrote:
> 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@xxxxxxxxxxxxxxxxxxx>
> > > Suggested-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Ricardo B. Marliere <ricardo@xxxxxxxxxxxx>
> > > ---
> > >    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?
Yes, this I mean. The example like this:

```c
   major = register_chrdev(0, xx, xx);
   class = class_create("bcachefs");
   if (IS_ERR(class))
        goto out_chrdev:

   ...
out_class:
    class_unregister(xxx);
out_chrdev:
    unregister_chrdev(xx, xx);
    ...
```

Although this was not part of your original intention, it is indeed a flaw.


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