netdev - Re: [PATCH 1/8] fwctl: Add basic structure for a class subsystem with a cdev

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Date: Wed, 5 Jun 2024 12:08:38 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Leon Romanovsky <leon@...nel.org>, Jonathan Corbet <corbet@....net>, Itay
 Avraham <itayavr@...dia.com>, Jakub Kicinski <kuba@...nel.org>,
	<linux-doc@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>, Saeed Mahameed
	<saeedm@...dia.com>, Tariq Toukan <tariqt@...dia.com>, Andy Gospodarek
	<andrew.gospodarek@...adcom.com>, Aron Silverton <aron.silverton@...cle.com>,
	Dan Williams <dan.j.williams@...el.com>, "David Ahern" <dsahern@...nel.org>,
	Christoph Hellwig <hch@...radead.org>, "Jiri Pirko" <jiri@...dia.com>, Leonid
 Bloch <lbloch@...dia.com>, <linux-cxl@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH 1/8] fwctl: Add basic structure for a class subsystem
 with a cdev

On Tue, 4 Jun 2024 15:52:00 -0300
Jason Gunthorpe <jgg@...dia.com> wrote:

> On Tue, Jun 04, 2024 at 06:05:55PM +0100, Jonathan Cameron wrote:
> 
> > Trick for this is often to define a small function that allocates both the
> > ida and the device. With in that micro function handle the one error path
> > or if you only have two things to do, you can use __free() for the allocation.  
> 
> This style is already followed here, the _alloc_device() is the
> function that does everything before starting reference counting (IMHO
> it is the best pattern to use). If we move the ida allocation to that
> function then the if inside release is not needed.
> 
> Like this:

LGTM (this specific code, not commenting on fwctl in general yet as needs
more thinking time!)

> 
> diff --git a/drivers/fwctl/main.c b/drivers/fwctl/main.c
> index d25b5eb3aee73c..a26697326e6ced 100644
> --- a/drivers/fwctl/main.c
> +++ b/drivers/fwctl/main.c
> @@ -267,8 +267,7 @@ static void fwctl_device_release(struct device *device)
>  	struct fwctl_device *fwctl =
>  		container_of(device, struct fwctl_device, dev);
>  
> -	if (fwctl->dev.devt)
> -		ida_free(&fwctl_ida, fwctl->dev.devt - fwctl_dev);
> +	ida_free(&fwctl_ida, fwctl->dev.devt - fwctl_dev);
>  	mutex_destroy(&fwctl->uctx_list_lock);
>  	kfree(fwctl);
>  }
> @@ -288,6 +287,7 @@ static struct fwctl_device *
>  _alloc_device(struct device *parent, const struct fwctl_ops *ops, size_t size)
>  {
>  	struct fwctl_device *fwctl __free(kfree) = kzalloc(size, GFP_KERNEL);
> +	int devnum;
>  
>  	if (!fwctl)
>  		return NULL;
> @@ -296,6 +296,12 @@ _alloc_device(struct device *parent, const struct fwctl_ops *ops, size_t size)
>  	init_rwsem(&fwctl->registration_lock);
>  	mutex_init(&fwctl->uctx_list_lock);
>  	INIT_LIST_HEAD(&fwctl->uctx_list);
> +
> +	devnum = ida_alloc_max(&fwctl_ida, FWCTL_MAX_DEVICES - 1, GFP_KERNEL);
> +	if (devnum < 0)
> +		return NULL;
> +	fwctl->dev.devt = fwctl_dev + devnum;
> +
>  	device_initialize(&fwctl->dev);
>  	return_ptr(fwctl);
>  }
> @@ -307,16 +313,10 @@ struct fwctl_device *_fwctl_alloc_device(struct device *parent,
>  {
>  	struct fwctl_device *fwctl __free(fwctl) =
>  		_alloc_device(parent, ops, size);
> -	int devnum;
>  
>  	if (!fwctl)
>  		return NULL;
>  
> -	devnum = ida_alloc_max(&fwctl_ida, FWCTL_MAX_DEVICES - 1, GFP_KERNEL);
> -	if (devnum < 0)
> -		return NULL;
> -	fwctl->dev.devt = fwctl_dev + devnum;
> -
>  	cdev_init(&fwctl->cdev, &fwctl_fops);
>  	fwctl->cdev.owner = THIS_MODULE;
>  
> Jason