[RFC PATCH] nvme: allow specific passthrough IOs without CAP_SYSADMIN

[Sagi Grimberg]

> The passthrough IOCTL interface allows for prototyping new non-standard
> NVMe features in userspace. However, all passthrough commands require
> full CAP_SYSADMIN over and above file access to the device. This means
> applications must run as root when running proof of concepts which is
> not often desirable.
> 
> Instead, relax that requirement for vendor specific commands as well
> as identify and get_log_page admin commands (which both have vendor
> specific components). Identify and get_log_page only query information
> from the controller so users with this privilege shouldn't be able to
> cause any negative side effects and vendor specific commands are the
> vendors responsibility to avoid dangerous side effects.
> 
> Users that want to send any of these passthrough commands will still
> require access to the NVMe char device or namespace. Typically, the
> char device is only accessible by root anyway and namespaces are
> accessible by root and the disk group. Administrators are free to
> add udev rules to adjust these permissions for specific devices they
> want to allow.

I don't understand what is the difference between VS commands and normal
commands? Why do you consider VS commands safe to relax privileges as
opposed to any other command?