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This patch introduces the file-system-session interface, provides an implementation of this interface in the form of an in-memory file system, and enables the libc to use the new file-system facility. The new interface resides in 'os/include/file_system_session/'. It uses synchronous RPC calls for functions referring to directory and meta-data handling. For transferring payload from/to files, the packet-stream interface is used. I envision that the asynchronous design of the packet-stream interface fits well will the block-session interface. Compared to Unix-like file-system APIs, Genode's file-system session interface is much simpler. In particular, it does not support per-file permissions. On Genode, we facilitate binding policy (such as write-permission) is sessions rather than individual file objects. As a reference implementation of the new interface, there is the new 'ram_fs' service at 'os/src/server/ram_fs'. It stores sparse files in memory. At the startup, 'ram_fs' is able to populate the file-system content with directories and ROM modules as specified in its configuration. To enable libc-using programs to access the new file-system interface, there is the new libc plugin at 'libports/src/lib/libc-fs'. Using this plugin, files stored on a native Genode file system can be accessed using the traditional POSIX file API. To see how the three parts described above fit together, the test case at 'libports/run/libc_fs' can be taken as reference. It reuses the original 'libc_ffat' test to exercise several file operations on a RAM file-system using the libc API. :Known limitations: The current state should be regarded as work in progress. In particular the error handling is not complete yet. Not all of the session functions return the proper exceptions in the event of an error. I plan to successively refine the interface while advancing the file-system implementations. Also the support for truncating files and symlink handling are not yet implemented. Furthermore, there is much room for optimization, in particular for the handling of directory entries. Currently, we communicate only one dir entry at a time, which is bad when traversing large trees. However, I decided to focus on functionality first and defer optimizations (such as batching dir entries) to a later stage. The current implementation does not handle file modification times at all, which may be a severe limitation for tools that depend on this information such as GNU make. Support for time will be added after we have revisited Genode's timer-session interface (issue #1). Fixes #54 Fixes #171
54 lines
1.3 KiB
C++
54 lines
1.3 KiB
C++
/*
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* \brief Server-side file-system session interface
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* \author Norman Feske
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* \date 2012-04-05
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*/
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/*
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* Copyright (C) 2012 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU General Public License version 2.
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*/
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#ifndef _INCLUDE__FILE_SYSTEM_SESSION__SERVER_H_
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#define _INCLUDE__FILE_SYSTEM_SESSION__SERVER_H_
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#include <file_system_session/file_system_session.h>
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#include <packet_stream_tx/rpc_object.h>
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#include <base/rpc_server.h>
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namespace File_system {
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class Session_rpc_object : public Genode::Rpc_object<Session, Session_rpc_object>
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{
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protected:
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Packet_stream_tx::Rpc_object<Tx> _tx;
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public:
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/**
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* Constructor
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*
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* \param tx_ds dataspace used as communication buffer
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* for the tx packet stream
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* \param ep entry point used for packet-stream channel
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*/
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Session_rpc_object(Dataspace_capability tx_ds, Rpc_entrypoint &ep)
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: _tx(tx_ds, ep) { }
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/**
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* Return capability to packet-stream channel
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*
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* This function is called by the client via an RPC call at session
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* construction time.
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*/
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Capability<Tx> _tx_cap() { return _tx.cap(); }
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Tx::Sink *tx_sink() { return _tx.sink(); }
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};
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}
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#endif /* _INCLUDE__FILE_SYSTEM_SESSION__SERVER_H_ */
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