This way we have four kinds of properties:
a) those which are constant as long as an object exists
b) those which can change and PropertiesChange messages with contents are generated
c) those which can change and where the PropertesChange merely includes invalidation
d) those which can change but for which no events are generated
Clients (through code generators run on the introspection XML) can thus
aggressively cache a, b, c, with only d excluded.
Internally, it makes sense to have a default of "privileged" for
methods, and a flag to open it up. However, externally in the bus
introspection turn this around since negative options actually suck.
When this flag is set then its member will not be shown in the
introspection data. Also, properties with this flag set will not be
included in GetAll() responses.
Introduces a new concept of "trusted" vs. "untrusted" busses. For the
latter libsystemd-bus will automatically do per-method access control,
for the former all access is automatically granted. Per-method access
control is encoded in the vtables: by default all methods are only
accessible to privileged clients. If the SD_BUS_VTABLE_UNPRIVILEGED flag
is set for a method it is accessible to unprivileged clients too. By
default whether a client is privileged is determined via checking for
its CAP_SYS_ADMIN capability, but this can be altered via the
SD_BUS_VTABLE_CAPABILITY() macro that can be ORed into the flags field
of the method.
Writable properties are also subject to SD_BUS_VTABLE_UNPRIVILEGED and
SD_BUS_VTABLE_CAPABILITY() for controlling write access to them. Note
however that read access is unrestricted, as PropertiesChanged messages
might send out the values anyway as an unrestricted broadcast.
By default the system bus is set to "untrusted" and the user bus is
"trusted" since per-method access control on the latter is unnecessary.
On dbus1 busses we check the UID of the caller rather than the
configured capability since the capability cannot be determined without
race. On kdbus the capability is checked if possible from the attached
meta-data of a message and otherwise queried from the sending peer.
This also decorates the vtables of the various daemons we ship with
these flags.
Message handler callbacks can be simplified drastically if the
dispatcher automatically replies to method calls if errors are returned.
Thus: add an sd_bus_error argument to all message handlers. When we
dispatch a message handler and it returns negative or a set sd_bus_error
we send this as message error back to the client. This means errors
returned by handlers by default are given back to clients instead of
rippling all the way up to the event loop, which is desirable to make
things robust.
As a side-effect we can now easily turn the SELinux checks into normal
function calls, since the method call dispatcher will generate the right
error replies automatically now.
Also, make sure we always pass the error structure to all property and
method handlers as last argument to follow the usual style of passing
variables for return values as last argument.
This patch converts PID 1 to libsystemd-bus and thus drops the
dependency on libdbus. The only remaining code using libdbus is a test
case that validates our bus marshalling against libdbus' marshalling,
and this dependency can be turned off.
This patch also adds a couple of things to libsystem-bus, that are
necessary to make the port work:
- Synthesizing of "Disconnected" messages when bus connections are
severed.
- Support for attaching multiple vtables for the same interface on the
same path.
This patch also fixes the SetDefaultTarget() and GetDefaultTarget() bus
calls which used an inappropriate signature.
As a side effect we will now generate PropertiesChanged messages which
carry property contents, rather than just invalidation information.
Old static libsystemd-bus.la becomes libsystemd-bus-internal.la.
memfd functions are also exported in the same library.
(Best viewed with --color-words -U0).
Among other things this also adds a few things necessary for the change:
- Considerably more powerful error returning APIs in libsystemd-bus
- Adapter for connecting an sd_bus to an sd_event
- As I reworked the PolicyKit logic to the new library I also made it
asynchronous, so that PolicyKit requests of one user cannot block out
another user anymore.
- We always use the macro names for common bus error. That way it is
harder to mistype them since the compiler will notice
One day sd-bus.h should become a public header file. We generally try to
be conservative in language features we use in public headers (much
unlike in private code), hence don't make use of anonymous unions in
structs for the vtable definitions.
Lennart Poettering