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