As mentioned earlier, a key goal of the Yocto Project is to present the
developer with
a kernel that has a clear and continuous history that is visible to the user.
The architecture and mechanisms used achieve that goal in a manner similar to the
upstream kernel.org
.
You can think of a Yocto Project kernel as consisting of a baseline Linux kernel with added features logically structured on top of the baseline. The features are tagged and organized by way of a branching strategy implemented by the source code manager (SCM) Git. For information on Git as applied to the Yocto Project, see the "Git" section in the Yocto Project Development Manual.
The result is that the user has the ability to see the added features and the commits that make up those features. In addition to being able to see added features, the user can also view the history of what made up the baseline kernel.
The following illustration shows the conceptual Yocto Project kernel.
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In the illustration, the "Kernel.org Branch Point" marks the specific spot (or release) from which the Yocto Project kernel is created. From this point "up" in the tree, features and differences are organized and tagged.
The "Yocto Project Baseline Kernel" contains functionality that is common to every kernel type and BSP that is organized further up the tree. Placing these common features in the tree this way means features do not have to be duplicated along individual branches of the structure.
From the Yocto Project Baseline Kernel, branch points represent specific functionality for individual BSPs as well as real-time kernels. The illustration represents this through three BSP-specific branches and a real-time kernel branch. Each branch represents some unique functionality for the BSP or a real-time kernel.
In this example structure, the real-time kernel branch has common features for all real-time kernels and contains more branches for individual BSP-specific real-time kernels. The illustration shows three branches as an example. Each branch points the way to specific, unique features for a respective real-time kernel as they apply to a given BSP.
The resulting tree structure presents a clear path of markers (or branches) to the developer that, for all practical purposes, is the kernel needed for any given set of requirements.