144 lines
5.1 KiB
C
144 lines
5.1 KiB
C
/*
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BeLock.h - interface to Fido-style message bases lock library.
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Copyright 2001-2003 Siarzhuk Zharski, imker@gmx.li
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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1. Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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3. All advertising materials mentioning features or use of this software
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must display the following acknowledgement:
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4. Neither the names of the authors nor the names of its contributors
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may be used to endorse or promote products derived from this software
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without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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SUCH DAMAGE.
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*/
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/*
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COMMENT: Many of Fidonet message bases uses file locks for theirs work in
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concurrent environment. The Be Operating System has not such possibility.
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Existing BeOS inplementations of locking allows to block only "nodes" from
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any access. This blocking cannot prevent from some "entry" modification
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attempts - for example, you can delete such file without problems or move
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it to somewhere. The node is still locked but it is not that we wait for.
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After long discussion on beos developer mail-lists I have not found usable
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solution for this problem. That's why I decide to implement some alternative
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locking technology. The key idea of my locking is using some BeOS-specific
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kernel objects. At this time I found only single one to be accessible from
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many processes - the BeOS kernel ports. See BeBook->Kernel Kit->Ports for
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details. We can create port with some name and we can look for port with
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such name in the system. Than, the locking algorithm is below:
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1) Get the device and node IDs for file handle we going to lock:
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fstat(file_handle, &stat_info);
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2) Create the name for the port to be used as locking object:
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sprintf(name, "FidoLock:%08X:%08X", stat_info.st_dev, stat_info.st_ino);
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3) Look for existing port with this name:
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pid = find_port(name);
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if(pid == B_NAME_NOT_FOUND)
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{
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4) Create such port.
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pid = create_port(1, name);
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}
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else
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{
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5) If such port exists - the file is locked - we must not touch it now -
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say calling program about failed lock.
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}
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To unlock locked file - just delete the port
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delete_port(pid);
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This technique is also not perfect, but, in my opinion it is more safe than
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node locking and more safe that work without any locking at al.
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*/
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#ifndef __BeLock_H_
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#define __BeLock_H_
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#include <OS.h>
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#ifdef __cplusplus
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extern "C" {
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#endif //__cplusplus
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/* be[os]_[f][un]lock() - acquires/releases file lock for file handle or stream
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parameters:
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file_handle - hanlde to file you want to [un]lock
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file - opened stream for file you want to [un]lock
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returns:
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be_* - set of functions:
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0 - on success
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-1 - on fails. See errno for error code and B_* - codes below.
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beos_* - set of functions:
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B_OK
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[0x00000000] - on success
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other codes on error:
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B_IO_ERROR (EIO)
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[0x80000001] - input/output error.
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For example fstat or fileno on file handles failed.
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B_NAME_NOT_FOUND
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[0x80000007] - port_name doesn't name an existing port.
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Try to unlock non-existing filelock.
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B_BAD_VALUE (EINVAL)
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[0x80000005] - port's queue_length is too big or less than zero.
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Error creating new port.
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B_NO_MORE_PORTS
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[0x80001201] - the system couldn't allocate another port.
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Error creating new port.
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B_BUSY (EBUSY)
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[0x8000000E] - file is already locked - port exists.
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B_BAD_PORT_ID
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[0x80001200] - port doesn't identify an open port.
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$Id$
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*/
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int be_lock(int file_handle);
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int be_unlock(int file_handle);
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int be_flock(FILE *file);
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int be_funlock(FILE *file);
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status_t beos_lock(int file_handle);
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status_t beos_unlock(int file_handle);
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status_t beos_flock(FILE *file);
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status_t beos_funlock(FILE *file);
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#ifdef __cplusplus
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} //extern "C"
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#endif //__cplusplus
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#endif // __BeLock_H_
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