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Support for socket-descriptor marshalling

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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 commit is contained in:
Norman Feske
2012-07-26 20:29:45 +02:00
parent 8b343d7e1a
commit ca4f574f4c
5 changed files with 270 additions and 60 deletions
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65
base-linux/include/base/ipc.h Normal file
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@ -0,0 +1,65 @@
/*
* \brief Linux-specific supplements to the IPC framework
* \author Norman Feske
* \date 2012-07-26
*/
/*
* Copyright (C) 2012 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU General Public License version 2.
*/
#ifndef _INCLUDE__BASE__IPC_H_
#define _INCLUDE__BASE__IPC_H_
#include <base/ipc_generic.h>
#include <base/snprintf.h>
extern "C" int raw_write_str(const char *str);
extern "C" void wait_for_continue(void);
#define PRAWW(fmt, ...) \
do { \
char str[128]; \
Genode::snprintf(str, sizeof(str), \
ESC_ERR fmt ESC_END "\n", ##__VA_ARGS__); \
raw_write_str(str); \
} while (0)
inline void Genode::Ipc_ostream::_marshal_capability(Genode::Native_capability const &cap)
{
PRAWW("_marshal_capability called: local_name=%ld, tid=%ld, socket=%d",
cap.local_name(), cap.dst().tid, cap.dst().socket);
_write_to_buf(cap.local_name());
_write_to_buf(cap.dst().tid);
if (cap.valid()) {
PRAWW("append_cap");
_snd_msg->append_cap(cap.dst().socket);
}
}
inline void Genode::Ipc_istream::_unmarshal_capability(Genode::Native_capability &cap)
{
long local_name = 0;
long tid = 0;
int socket = -1;
_read_from_buf(local_name);
_read_from_buf(tid);
bool const cap_valid = (tid != 0);
if (cap_valid)
socket = _rcv_msg->read_cap();
cap = Native_capability(Cap_dst_policy::Dst(tid, socket), local_name);
}
#endif /* _INCLUDE__BASE__IPC_H_ */