Why I did it
Support to use symbol links in platform folder to reduce the image size.
The current solution is to copy each lazy installation targets (xxx.deb files) to each of the folders in the platform folder. The size will keep growing when more and more packages added in the platform folder. For cisco-8000 as an example, the size will be up to 2G, while most of them are duplicate packages in the platform folder.
How I did it
Create a new folder in platform/common, all the deb packages are copied to the folder, any other folders where use the packages are the symbol links to the common folder.
Why platform.tar?
We have implemented a patch for it, see #10775, but the problem is the the onie use really old unzip version, cannot support the symbol links.
The current solution is similar to the PR 10775, but make the platform folder into a tar package, which can be supported by onie. During the installation, the package.tar will be extracted to the original folder and removed.
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