Struct BackingState 

struct BackingState {
    segments: Vec<FramebufferSegment>,
    size: usize,
    external: bool,
}

Backing-store state for the scanout resource.

Held behind a Mutex so a physically-contiguous buffer allocated after device init (the video driver’s double buffer) can be attached as the resource backing itself, making presentation zero-copy: draw targets become what TRANSFER_TO_HOST_2D reads, no bounce copy needed.

Fields

segments: Vec<FramebufferSegment>

HHDM-mapped segments covering the backing store, in offset order.

size: usize

Total backing size in bytes.

external: bool

True when the backing is an externally provided contiguous buffer (attach_external_backing) rather than driver-scattered pages.