From 45435cc7e158eb4a604bc541575799ee603b14db Mon Sep 17 00:00:00 2001 From: Mattias Andrée Date: Wed, 30 Dec 2015 02:15:02 +0100 Subject: add reopen MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Signed-off-by: Mattias Andrée --- src/fcntl/reopen.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) create mode 100644 src/fcntl/reopen.c (limited to 'src') diff --git a/src/fcntl/reopen.c b/src/fcntl/reopen.c new file mode 100644 index 0000000..e689e58 --- /dev/null +++ b/src/fcntl/reopen.c @@ -0,0 +1,79 @@ +/** + * slibc — Yet another C library + * Copyright © 2015 Mattias Andrée (maandree@member.fsf.org) + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see . + */ +#include +#include +#include +#include + + + +/** + * Reopen a file via its file descriptor. The old file descriptor + * is closed and replace with the new open file descriptor. + * + * This function call is different from the `dup` function-family + * in two ways: (1) you can select news flags, for example, if + * `fd` was read-only, the new file descriptor can be write-only, + * and (2) the file descriptor is not duplicated, the file is + * reopened. + * + * This function is useful if you want to reopen a file you do + * now know the pathname, you do not want to create a new string + * with the pathname, or if the the file no longer has a pathname + * because it has been unlinked. + * + * Because the file is reopened, the file position is reset and + * is not shared with any duplicates of `fd`, unlike a call to + * dup(3). it is visible to the filesystem as a new open file + * descriptor and is distinguished from the duplocates of `fd`, + * and all file locks associated with `fd` are lost, except for + * on the duplicates of `fd`, which means that you can create + * new locks without removing locks from the duplicates of `fd`. + * + * This is a slibc extension. + * + * @etymology (Reopen) file! + * + * @param fd The file descriptor. + * @param oflag How the file shall be opened, see open(3). + * `O_CREAT` is not allowed. + * @return Zero on success, -1 on error. + * + * @throws EINVAL `oflag` contains `O_CREAT`. + * @throws EINVAL `fd` is negative. + * @throws Any error specified for open(3). + * @throws Any error specified for dup2(3). + * + * @since Always. + */ +int reopen(int fd, int oflag) +{ + char path[sizeof("/dev/fd/") + 3 * sizeof(int)]; + int r, saved_errno; + + if ((oflag & O_CREAT) || (fd < 0)) + return errno = EINVAL, -1; + + sprintf(path, "/dev/fd/%i", fd); + if (r = open(path, oflag), r < 0) + return -1; + if (dup2(r, fd) == -1) + return saved_errno = errno, close(r), errno = saved_errno, -1; + return close(fd), 0; +} + -- cgit v1.2.3-70-g09d2