118 lines
3.8 KiB
C
118 lines
3.8 KiB
C
/****************************************************************************
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* libs/libc/unistd/lib_lockf.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: lockf
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*
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* Description:
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* lockf() 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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* F_LOCK: Request an exclusive (write) lock. If the lock is not
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* available, the call may block until it can be acquired.
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* F_TLOCK: Try to request an exclusive (write) lock. If the lock is not
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* available, the call will not block and will return
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* immediately.
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* F_ULOCK: Unlock an existing lock.
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* F_TEST: Test the lock. Returns 0 if the file is unlocked or locked by
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* the calling process, or -1 with errno set to EACCES if another
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* process holds the lock.
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* len - Length of the locked region, relative to the current file
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* position.
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*
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* Returned Value:
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* The returned value of lockf() 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 lockf(int fd, int cmd, off_t len)
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{
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struct flock lock;
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lock.l_whence = SEEK_CUR;
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lock.l_start = 0;
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lock.l_len = len;
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switch (cmd)
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{
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case F_LOCK:
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{
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lock.l_type = F_WRLCK;
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return fcntl(fd, F_SETLKW, &lock);
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}
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case F_TLOCK:
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{
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lock.l_type = F_WRLCK;
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return fcntl(fd, F_SETLK, &lock);
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}
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case F_ULOCK:
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{
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lock.l_type = F_UNLCK;
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return fcntl(fd, F_SETLK, &lock);
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}
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case F_TEST:
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{
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lock.l_type = F_RDLCK;
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if (fcntl(fd, F_GETLK, &lock) < 0)
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{
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return ERROR;
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}
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/* Check result */
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if (lock.l_type == F_UNLCK || lock.l_pid == getpid())
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{
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return OK;
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}
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set_errno(EACCES);
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return ERROR;
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}
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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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