Re: gentoo with 270.30 - broken /usr/bin/nvidia-smi (requires libnvidia-ml.so.1)
That's probably a Gentoo packaging bug.
libnvidia-ml is the NVIDIA Management Library. The cross-platform NVML API provides functions for querying and configuring the GPU. nvidia-smi, which was formerly a standalone app, is now an NVML client.
Since the libnvidia-ml DSO is new in the 270.xx drivers, it seems likely that some distro maintainers might have missed it when repackaging the driver.