Re: [PATCH] gpiolib: cdev: add fdinfo output for line request file descriptors

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Tue, Sep 20, 2022 at 03:54:35PM +0200, Bartosz Golaszewski wrote:
> Add fdinfo output for file descriptors created for user-space line
> requests in GPIO uAPI v2. The fdinfo file now contains the name of the
> GPIO device that is the "parent" of the request as well as offsets of
> the lines requested. This allows user-space to parse the /proc/$PID/fdinfo
> entries and deduct the PID of the process that requested a specific line.

In principle I'm fine, but see below.

> Signed-off-by: Bartosz Golaszewski <brgl@xxxxxxxx>
> ---
>  drivers/gpio/gpiolib-cdev.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index f8041d4898d1..0f7b5562c410 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -1497,6 +1497,21 @@ static int linereq_release(struct inode *inode, struct file *file)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_PROC_FS
> +static void linereq_show_fdinfo(struct seq_file *out, struct file *file)
> +{
> +	struct linereq *lr = file->private_data;
> +	struct device *dev = &lr->gdev->dev;
> +	u16 i;
> +
> +	seq_printf(out, "gpio-device:\t%s\n", dev_name(dev));
> +
> +	for (i = 0; i < lr->num_lines; i++)
> +		seq_printf(out, "gpio-line:\t%d\n",
> +			   gpio_chip_hwgpio(lr->lines[i].desc));

Hmm... Not sure which variant is better (as for machine parsing and for human),
but I was thinking of

	gpio-lines: 1,4,6, ...

Also don't forget that sizes over PAGE_SIZE in sysfs sometimes problematic and
racy.(the commit 888be6067b97 ("ACPI: sysfs: Fix a buffer overrun problem with
description_show()") for the reference).

> +}
> +#endif
> +
>  static const struct file_operations line_fileops = {
>  	.release = linereq_release,
>  	.read = linereq_read,
> @@ -1507,6 +1522,9 @@ static const struct file_operations line_fileops = {
>  #ifdef CONFIG_COMPAT
>  	.compat_ioctl = linereq_ioctl_compat,
>  #endif
> +#ifdef CONFIG_PROC_FS
> +	.show_fdinfo = linereq_show_fdinfo,
> +#endif
>  };
>  
>  static int linereq_create(struct gpio_device *gdev, void __user *ip)
> -- 
> 2.34.1
> 

-- 
With Best Regards,
Andy Shevchenko