96 lines
3.1 KiB
C
96 lines
3.1 KiB
C
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/****************************************************************************
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* libs/libc/unistd/lib_flock.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <unistd.h>
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#include <fcntl.h>
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#include <errno.h>
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: flock
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*
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* Description:
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* flock() is a function that allows a process to apply or remove an
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* advisory lock on an open file. The lock can be either a shared (read)
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* lock or an exclusive (write) lock. This lock is advisory, meaning that
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* it is not enforced by the system and it is up to cooperating processes
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* to honor the lock.
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*
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* Input Parameters:
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* fd - File descriptor of the open file.
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* cmd - Specifies the type of lock operation to be performed.
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* It can be one of the following:
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* LOCK_SH: Request a shared (read) lock. If the lock is not available.
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* LOCK_EX: Request an exclusive (write) lock. If the lock is not
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* available.
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* LOCK_UN: Unlock an existing lock.
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* LOCK_NB: Do not block when locking.
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*
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* Returned Value:
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* The returned value of flock() depends on the success or failure of the
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* operation. On success, the return value is 0. On failure, the return
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* value is -1, and the errno variable is set to indicate the specific
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* error.
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*
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****************************************************************************/
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int flock(int fd, int cmd)
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{
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struct flock lock;
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lock.l_whence = SEEK_SET;
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lock.l_start = 0;
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lock.l_len = 0;
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if ((cmd & LOCK_SH) != 0)
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{
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lock.l_type = F_RDLCK;
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}
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else if ((cmd & LOCK_EX) != 0)
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{
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lock.l_type = F_WRLCK;
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}
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else if ((cmd & LOCK_UN) != 0)
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{
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lock.l_type = F_UNLCK;
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}
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else
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{
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set_errno(EINVAL);
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return ERROR;
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}
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if ((cmd & LOCK_NB) != 0)
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{
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return fcntl(fd, F_SETLK, &lock);
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}
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else
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{
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return fcntl(fd, F_SETLKW, &lock);
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}
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}
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