> On Jun 26, 2019, at 5:08 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, Jun 26, 2019 at 03:17:47PM +0000, Song Liu wrote:
>>>> +static struct miscdevice bpf_dev = {
>>>> + .minor = MISC_DYNAMIC_MINOR,
>>>> + .name = "bpf",
>>>> + .fops = &bpf_chardev_ops,
>>>> + .mode = 0440,
>>>> + .nodename = "bpf",
>>>
>>> Here's what kvm does:
>>>
>>> static struct miscdevice kvm_dev = {
>>> KVM_MINOR,
>>> "kvm",
>>> &kvm_chardev_ops,
>>> };
>
> Ick, I thought we converted all of these to named initializers a long
> time ago :)
>
>>> Is there an actual reason that mode is not 0 by default in bpf case? Why
>>> we need to define nodename?
>>
>> Based on my understanding, mode of 0440 is what we want. If we leave it
>> as 0, it will use default value of 0600. I guess we can just set it to
>> 0440, as user space can change it later anyway.
>
> Don't rely on userspace changing it, set it to what you want the
> permissions to be in the kernel here, otherwise you have to create a new
> udev rule and get it merged into all of the distros. Just do it right
> the first time and there is no need for it.
>
> What is wrong with 0600 for this? Why 0440?
We would like root to own the device, and let users in a certain group
to be able to open it. So 0440 is what we need.
Thanks,
Song
