linux-kernel - Re: [PATCH 05/14] cxl/mem: Register CXL memX devices

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Date:   Tue, 2 Feb 2021 18:13:54 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     linux-cxl@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-pci@...r.kernel.org,
        Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        daniel.lll@...baba-inc.com,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>
Subject: Re: [PATCH 05/14] cxl/mem: Register CXL memX devices

> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 25e08e5f40bd..33432a4cbe23 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3179,6 +3179,20 @@ struct device *get_device(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(get_device);
>  
> +/**
> + * get_live_device() - increment reference count for device iff !dead
> + * @dev: device.
> + *
> + * Forward the call to get_device() if the device is still alive. If
> + * this is called with the device_lock() held then the device is
> + * guaranteed to not die until the device_lock() is dropped.
> + */
> +struct device *get_live_device(struct device *dev)
> +{
> +	return dev && !dev->p->dead ? get_device(dev) : NULL;
> +}
> +EXPORT_SYMBOL_GPL(get_live_device);

Err, if you want to add new core functionality that needs to be in a
separate well documented prep patch, and also CCed to the relevant
maintainers.

>  	mutex_unlock(&cxlm->mbox.mutex);
>  }
>  
> +static int cxl_memdev_open(struct inode *inode, struct file *file)
> +{
> +	struct cxl_memdev *cxlmd =
> +		container_of(inode->i_cdev, typeof(*cxlmd), cdev);
> +
> +	file->private_data = cxlmd;

There is no good reason to ever mirror stuff from the inode into
file->private_data, as you can just trivially get at the original
location using file_inode(file).