This patch simplifies the system call bindings. The common syscall
bindings in 'src/platform/' have been reduced to the syscalls needed by
non-core programs. The additional syscalls that are needed solely by
core have been moved to 'src/core/include/core_linux_syscalls.h'.
Furthermore, the resource path is not used outside of core anymore.
Hence, we could get rid of the rpath library. The resource-path code has
been moved to 'src/core/include/resource_path.h'. The IPC-related parts
of 'src/platform' have been moved to the IPC library. So there is now a
clean separation between low-level syscall bindings (in 'src/platform')
and higher-level code.
The code for the socket-descriptor registry is now located in the
'src/base/ipc/socket_descriptor_registry.h' header. The interface is
separated from 'ipc.cc' because core needs to access the registry from
outside the ipc library.
This patch changes the way of how dataspace content is accessed by
processes outside of core. Dataspaces are opened by core only and the
corresponding file descriptors are handed out the other processes via
the 'Linux_dataspace::fd()' RPC function. At the client side, the
returned file descriptor is then used to mmap the file.
Consequently, this patch eliminates all files from 'lx_rpath'. The
path is still needed by core to temporarily create dataspaces and
unix domain sockets. However, those files are unlinked immediately
after their creation.
This patch eliminates the thread ID portion of the 'Native_capability'
type. The access to entrypoints is now exclusively handled by passing
socket descripts over Unix domain sockets and by inheriting the socket
descriptor of the parent entrypoint at process-creation time.
Each entrypoint creates a socket pair. The server-side socket is bound
to a unique name defined by the server. The client-side socket is then
connected to the same name. Whereas the server-side socket is meant to
be exclusively used by the server to wait for incoming requests, the
client-side socket can be delegated to other processes as payload of RPC
messages (via SCM rights). Anyone who receives a capability over RPC
receives the client-side socket of the entrypoint to which the
capability refers. Given this socket descriptor, the unique name (as
defined by the server) can be requested using 'getpeername'. Using this
name, it is possible to compare socket descriptors, which is important
to avoid duplicates from polluting the limited socket-descriptor name
space.
Wheras this patch introduces capability-based delegation of access
rights to entrypoints, it does not cover the protection of the integrity
of RPC objects. RPC objects are still referenced by a global ID passed
as normal message payload.
This patch adds prinicipal support for transmitting socket descriptors
as RPC payload. Socket descriptors are handled by the linux-specific
implementation of the capability marshalling and unmarshalling functions
in 'ipc.h'. The 'Message' type in 'src/platform/linux_socket.h' has been
extended to carry multiple descriptors in a single message.
Unfortuately, we hit a problem (and potential show stopper) here:
lx_sendmsg failed with -109 in lx_call()
The error code corresponds to ETOOMANYREFS. There is only one place in
the Linux kernel where this error code is used (net/unix/af_unix.c).
The code for 'unix_attach_fds()' suggests that there is a limit with
regard to the maximum number of references for a given Unix domain
socket. When the error occurs, core and init are running. The socket
of core's server entrypoint is present in the '/proc/pid/fd' of those
processes 8 times. The error occurs when core tries to perform an
RPC to the entrypoint to perform 'Ram_session::transfer_quota()'
(base/include/base/child.h at line 248).
This patch, which was originally created by Christian Helmuth,
represents the first step towards using SCM rights as capability
mechanism on Linux. It employs the SCM rights mechanism for transmitting
a reply capability to the server as argument of each IPC call. The
server will then send its respond to this reply file descriptor. This
way, the reply channel does not need to be globally visible anymore.
Setting the handler for SIGCHLD to SIG_IGN (ignore) informs the kernel
not to enter the zombie state: (man 2 wait)
POSIX.1-2001 specifies that if the disposition of SIGCHLD is set to
SIG_IGN or the SA_NOCLDWAIT flag is set for SIGCHLD (see
sigaction(2)), then children that terminate do not become zombies
[...]
Fixes#271.
