Function get_gpu_driver 

pub(crate) fn get_gpu_driver(card_index: i32) -> String

Read the kernel driver bound to a render node for encoder routing.

An nvidia driver name routes to NVENC; anything else routes to VA-API. The name is lowercased for case-insensitive substring matching, and is empty when the node has no driver link (treated as “no detectable GPU” by the selection logic).

sysfs lists every card the kernel sees, not the ones this process was given: a container handed a single GPU still finds the host’s others under /sys/class/drm. A driver read from a node with no device file would route the encoder at hardware it cannot open, so an absent node answers the same as an unknown one.

Arguments

• card_index - DRM card index (maps to /sys/class/drm/renderD{128 + card_index}).

Returns

Lowercased driver name, or an empty string if the node is unusable or has no driver link.