RAM Quota Forwarding

[Norman Feske]

Hello Ben,

On 27.03.2016 08:19, Nobody III wrote:
> I made a service router that subclasses Genode::Root, and I've gotten it
> to work, but I'm unsure of how to properly implement RAM quota
> forwarding. How do I implement this?

I am afraid that your question is a bit vague to give you a definite answer.

If your component merely wraps an existing session, it receives the
session quotas of the actual clients when the respective client opens a
session. The quota transfer happens at the common parent (e.g., init).
The transfer is done in two steps: 1) from the client's RAM session to
the parent's RAM session, and 2) from the parent's RAM session to the
server's RAM session. The amount of quota to be transferred is specified
via the "ram_quota" session argument given by the client. It is usually
defined by the session-specific 'Connection' classes.

An intermediate component (like your's) can "forward" the client's
session quota by specifying the same amount it finds in the client's
session args (the quota it already received) as "ram_quota" argument
when creating the session at the real server. The parent will do the
actual transfer.

Please note that a client may upgrade session quota after the initial
session creation. This is usually the case when the needed quota is not
known at the session-creation time (e.g., for Nitpicker). The underlying
procedure looks very similarly to the session creation, but it uses the
Parent::upgrade_quota and Root::upgrade_quota functions. Your
intermediate component should implement those functions to play well
with such services.

Cheers
Norman

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Dr.-Ing. Norman Feske
Genode Labs

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