This patch replaces the former prominent use of pointers by references
wherever feasible. This has the following benefits:
* The contract between caller and callee becomes more obvious. When
passing a reference, the contract says that the argument cannot be
a null pointer. The caller is responsible to ensure that. Therefore,
the use of reference eliminates the need to add defensive null-pointer
checks at the callee site, which sometimes merely exist to be on the
safe side. The bottom line is that the code becomes easier to follow.
* Reference members must be initialized via an object initializer,
which promotes a programming style that avoids intermediate object-
construction states. Within core, there are still a few pointers
as member variables left though. E.g., caused by the late association
of 'Platform_thread' objects with their 'Platform_pd' objects.
* If no pointers are present as member variables, we don't need to
manually provide declarations of a private copy constructor and
an assignment operator to avoid -Weffc++ errors "class ... has
pointer data members [-Werror=effc++]".
This patch also changes a few system bindings on NOVA and Fiasco.OC,
e.g., the return value of the global 'cap_map' accessor has become a
reference. Hence, the patch touches a few places outside of core.
Fixes#3135
When capabilities are delegated to components, they are added to the UTCB of the
target thread. Before the thread is able to take out the capability id out of
the UTCB and adapt the user-level capability reference counter, it might happen
that another thread of the same component deletes the same capability because
its user-level reference counter reached zero. If the kernel then destroys the
capability, before the same capability id is taken out of all UTCBs, an
inconsitent view in the component is the result. To keep an consistent view in
the multi-threading scenario, the kernel now counts how often it puts a
capability into a UTCB. The threads on the other hand hint the kernel when they
took capabilities out of the UTCB, so the kernel can decrement the counter
again. Only when the counter is zero, capabilities can get destructed.
Fix#1623
Emery Hemingway
Norman Feske
Stefan Kalkowski