Protect muvm-server, spawn one as root and monitor available host memory #89
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While our threat model targets single user systems, let's at least protect muvm-server with an authentication cookie, so only the user creating the microVM (and root) can access it. The cookie is stored in the lockfile, instead of the server port (this was useless in practice and generated confusion as could override the command line). The lockfile is located in XDG_RUNTIME_DIR, which in properly configured systems is only accessible to its owner. Signed-off-by: Sergio Lopez <slp@redhat.com>
Being able to run commands as root comes handy to debug the guest and will also be used to tune the virtual memory parameters on demand. Signed-off-by: Sergio Lopez <slp@redhat.com>
This monitor checks the ratio of memory available on the host and, if needed, contacts the VM (through muvm-server) to adjust /proc/sys/vm/watermark_scale_factor and, if the situation is critical, to request it to drop its caches. Signed-off-by: Sergio Lopez <slp@redhat.com>
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The goal of this PR is to enable muvm to request the guest to adjust its file system cache goals accordingly to the amount of available memory on the host.
The first two commits just set the infrastructure, first by adding some minimal protection to muvm-server, and then spawning a second instance of it as root (we need this to operate in "/proc/sys/vm", but surely will come handy for many other things).
The latter implements the monitor and the ability to request the guest to adjust watermark_scale_factor as needed, or even to drop its pagecache if the situation is critical.