Layouts: re-mapping snap directories

Hey

I’d like to describe an upcoming feature of snapd, that was designed on a sprint recently. The keyword is layouts and it will empower snap developers to alter the mount namespace in which their applications execute in ways not possible before.

The general idea is that a snap can statically declare it wants to take some content and put it somewhere in the filesystem. The content can come from the snap itself, from the snap system-wide data. This will, for example, allow us to create the impression that a given directory is mounted in /var/lib or a particular file exists in /etc/. This should allow snap developers to overcome hardships of hard-coded locations common to many libraries and packages.

Unlike interfaces, such as the content interface, layouts cannot be “disconnected”. Anyone that designs a snap can do so taking advantage of the fact that before their code runs the layout will be already in place.
Layous can also evolve over time so subsequent revisions of a snap can change the layout as the need arises.

In subsequent posts I will describe the feature both semantically, from developer point of view, as well as technically to show how it will be implemented. Feel free to join the conversation and ask questions.

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