Dtbo

A device tree blob overlay, abbreviated as dtbo, is a compiled device tree fragment designed to modify a base device tree blob (DTB) without changing the original DTB. It enables hardware configurations to be added to or overridden in a modular way, supporting device variants and add-on components.

Dtbo files are created from Device Tree Source (DTS) files that describe small fragments, including a target node and a set of properties to add or override. The fragments are assembled into a single overlay and compiled with the device tree compiler into a binary .dtbo file. The overlay mechanism allows multiple fragments to be applied to a single base DTB, in a defined order, to tailor the hardware description to a specific device revision or configuration.

In Linux-based systems, dtbo support allows the kernel to apply overlays at boot or runtime, depending on the platform and bootloader. In Android, device-specific overlays are commonly stored in a dtbo partition or packaged with vendor data. During boot, the kernel or bootloader merges the overlays with the base DTB, resulting in a final device tree that reflects the actual hardware present.

File organization and usage: dtbo files typically have the .dtbo extension. They originate from DTS sources and are loaded by the system’s overlay manager or kernel support, which applies them to the base DTB. Overlays are additive by design, meaning they modify or augment existing nodes and properties rather than replacing the entire tree. Proper ordering and compatibility are essential to avoid conflicts.

Limitations and considerations: overlays can’t universally rewrite every aspect of a DTB; some properties remain constrained by the base DTB and platform firmware. Overlays may introduce security or stability concerns if misused, and not all kernels support runtime overlay loading.