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The VFS library can be used in single-threaded or multi-threaded environments and depending on that, signals are handled by the same thread which uses the VFS library or possibly by a different thread. If a VFS plugin needs to block to wait for a signal, there is currently no way which works reliably in both environments. For this reason, this commit makes the interface of the VFS library nonblocking, similar to the File_system session interface. The most important changes are: - Directories are created and opened with the 'opendir()' function and the directory entries are read with the recently introduced 'queue_read()' and 'complete_read()' functions. - Symbolic links are created and opened with the 'openlink()' function and the link target is read with the 'queue_read()' and 'complete_read()' functions and written with the 'write()' function. - The 'write()' function does not wait for signals anymore. This can have the effect that data written by a VFS library user has not been processed by a file system server yet when the library user asks for the size of the file or closes it (both done with RPC functions at the file system server). For this reason, a user of the VFS library should request synchronization before calling 'stat()' or 'close()'. To make sure that a file system server has processed all write request packets which a client submitted before the synchronization request, synchronization is now requested at the file system server with a synchronization packet instead of an RPC function. Because of this change, the synchronization interface of the VFS library is now split into 'queue_sync()' and 'complete_sync()' functions. Fixes #2399 |
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| .. | ||
| directory.h | ||
| file.h | ||
| lx_util.h | ||
| main.cc | ||
| node.h | ||
| README | ||
| symlink.h | ||
| target.mk | ||
This directory contains an Genode file-system service to Linux host fs wrapper. Configuration ~~~~~~~~~~~~~ Access to the file system can be tailored for each session depending on the session's label. By default, no permissions are granted to any session. To selectively permit access to (a part of) the file system, at least one policy must be defined. The following configuration illustates the way of how to express policy. ! <config> ! <!-- constrain sessions according to their labels --> ! <policy label="noux -> root" root="/" /> ! <policy label="noux -> home" root="/home/user" writeable="yes" /> ! <policy label="noux -> tmp" root="/tmp" writeable="yes" /> ! </config> Session-specific access-control policy is expressed via one or more '<policy>' nodes. At session-creation time, each policy node is matched against the label of the new session. If the label of a policy node matches, the defined policy is applied. If multiple policies match, the one with the longest 'label' attribute (the most specific one) is selected. A policy node may contain the following attributes. The mandatory 'root' attribute defines the viewport of the session onto the file system. The optional 'writeable' attribute grants the permission to modify the file system. Example ~~~~~~~ To illustrate the use of lx_fs, refer to the 'base-linux/run/lx_fs.run' script. Notes ~~~~~ If the Linux file system experiences changes from other processes 'inotify' may help to keep the servers cache up-to-date. This is not implemented yet.