When multiple containers run inside a sentry, each container has its own root
filesystem and set of mounts. Containers are also added after sentry boot rather
than all configured and known at boot time.
The fsgofer needs to be able to serve the root filesystem of each container.
Thus, it must be possible to add filesystems after the fsgofer has already
started.
This change:
* Creates a URPC endpoint within the gofer process that listens for requests to
serve new content.
* Enables the sentry, when starting a new container, to add the new container's
filesystem.
* Mounts those new filesystems at separate roots within the sentry.
PiperOrigin-RevId: 208903248
Change-Id: Ifa91ec9c8caf5f2f0a9eead83c4a57090ce92068
Docker expects containers to be created before they are restored.
However, gVisor restoring requires specificactions regarding the kernel
and the file system. These actions were originally in booting the sandbox.
Now setting up the file system is deferred until a call to a call to
runsc start. In the restore case, the kernel is destroyed and a new kernel
is created in the same process, as we need the same process for Docker.
These changes required careful execution of concurrent processes which
required the use of a channel.
Full docker integration still needs the ability to restore into the same
container.
PiperOrigin-RevId: 205161441
Change-Id: Ie1d2304ead7e06855319d5dc310678f701bd099f
Ian Gudger
Kevin Krakauer
Justine Olshan
Googler