Re: [PATCH] PCI/sysfs: add write attribute for boot_vga

From: Krzysztof Wilczyński
Date: Sun Sep 26 2021 - 16:01:00 EST

[+cc Huacai and Kai-Heng as they are working in this area]


Thank you for sending the patch over.

I assume this is simply a resend (rather than a v2), as I see no code
changes from the previous version you sent some time ago.

> Add writing attribute for boot_vga sys node,
> so we can config default video display
> output dynamically when there are two video
> cards on a machine.

That's OK, but why are you adding this? What problem does it solve and
what is the intended user here? Might be worth adding a little bit more
details about why this new sysfs attribute is needed.

I also need to ask, as I am not sure myself, whether this is OK to do after
booting during runtime? What do you think Bjorn, Huacai and Kai-Heng?

Also, please correctly capitalise the subject - have a look at previous
commit messages to see how it should look like.

> +static ssize_t boot_vga_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + unsigned long val;
> + struct pci_dev *pdev = to_pci_dev(dev);
> + struct pci_dev *vga_dev = vga_default_device();
> +
> + if (kstrtoul(buf, 0, &val) < 0)
> + return -EINVAL;
> +
> + if (val != 1)
> + return -EINVAL;

Since this is a completely new API have a look at kstrtobool() over
kstrtoul() as the former was created to handle user input more

> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +

Check for CAP_SYS_ADMIN is a good idea, but it has to take place before you
attempt to accept and parse a input from the user.