I'm tired of seeing this done incorrectly and non-portably, so add a
flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
This commit is contained in:
parent
703ec91e6a
commit
9667055264
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=169446
@ -8,11 +8,11 @@ SHLIBDIR?= /lib
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LIB= util
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SHLIB_MAJOR= 6
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SRCS= _secure_path.c auth.c fparseln.c humanize_number.c kld.c login.c \
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login_auth.c login_cap.c login_class.c login_crypt.c login_ok.c \
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login_times.c login_tty.c logout.c logwtmp.c \
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pidfile.c property.c pty.c pw_util.c realhostname.c stub.c \
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trimdomain.c uucplock.c
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SRCS= _secure_path.c auth.c flopen.c fparseln.c humanize_number.c \
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kld.c login.c login_auth.c login_cap.c login_class.c \
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login_crypt.c login_ok.c login_times.c login_tty.c logout.c \
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logwtmp.c pidfile.c property.c pty.c pw_util.c realhostname.c \
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stub.c trimdomain.c uucplock.c
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INCS= libutil.h login_cap.h
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CFLAGS+= -DLIBC_SCCS
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@ -27,7 +27,7 @@ MAN+= kld.3 login.3 login_auth.3 login_tty.3 logout.3 logwtmp.3 pty.3 \
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login_cap.3 login_class.3 login_times.3 login_ok.3 \
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_secure_path.3 uucplock.3 property.3 auth.3 realhostname.3 \
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realhostname_sa.3 trimdomain.3 fparseln.3 humanize_number.3 \
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pidfile.3
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pidfile.3 flopen.3
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MAN+= login.conf.5 auth.conf.5
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MLINKS+= kld.3 kld_isloaded.3 kld.3 kld_load.3
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MLINKS+= property.3 properties_read.3 property.3 properties_free.3
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79
lib/libutil/flopen.3
Normal file
79
lib/libutil/flopen.3
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@ -0,0 +1,79 @@
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.\"-
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.\" Copyright (c) 2007 Dag-Erling Coïdan Smørgrav
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.\" All rights reserved.
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.\"
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd May 10, 2007
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.Dt FLOPEN 3
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.Os
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.Sh NAME
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.Nm flopen
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.Nd "Reliably open and lock a file"
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.Sh LIBRARY
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.Lb libutil
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.Sh SYNOPSIS
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.In sys/fcntl.h
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.In libutil.h
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.Ft int
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.Fn flopen "const char *path" "int flags"
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.Ft int
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.Fn flopen "const char *path" "int flags" "mode_t mode"
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.Sh DESCRIPTION
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The
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.Fn flopen
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function opens or creates a file and acquires an exclusive lock on it.
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It is essentially equivalent with calling
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.Fn open
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with the same parameters followed by
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.Fn flock
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with an
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.Va operation
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argument of
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.Dv LOCK_EX ,
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except that
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.Fn flopen
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will attempt to detect and handle races that may occur between opening
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/ creating the file and locking it.
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Thus, it is well suited for opening lock files, PID files, spool
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files, mailboxes and other kinds of files which are used for
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synchronization between processes.
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.Pp
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As with
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.Fn flopen ,
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the additional
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.Va mode
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argument is required if
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.Va flags
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includes
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.Dv O_CREAT .
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.Sh SEE ALSO
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.Xr flock 2 ,
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.Xr open 2
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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function and this manual page were written by
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.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org .
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91
lib/libutil/flopen.c
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91
lib/libutil/flopen.c
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@ -0,0 +1,91 @@
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/*-
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* Copyright (c) 2007 Dag-Erling Coïdan Smørgrav
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* All rights reserved.
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*
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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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* in this position and unchanged.
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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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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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* $Id$
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/stat.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdarg.h>
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int
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flopen(const char *path, int flags, ...)
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{
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struct stat sb, fsb;
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mode_t mode;
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int fd, serrno;
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#ifdef O_EXLOCK
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flags &= ~O_EXLOCK;
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#endif
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if (flags & O_CREAT) {
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va_list ap;
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va_start(ap, flags);
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mode = va_arg(ap, int); /* mode_t promoted to int */
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va_end(ap);
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} else {
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mode = 0;
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}
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for (;;) {
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if ((fd = open(path, flags, mode)) == -1)
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/* non-existent or no access */
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return (-1);
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if (flock(fd, LOCK_EX) == -1) {
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/* unsupported or interrupted */
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serrno = errno;
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close(fd);
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errno = serrno;
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return (-1);
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}
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if (stat(path, &sb) == -1) {
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/* disappeared from under our feet */
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close(fd);
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continue;
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}
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if (fstat(fd, &fsb) == -1) {
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/* can't happen [tm] */
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serrno = errno;
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close(fd);
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errno = serrno;
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return (-1);
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}
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if (sb.st_dev != fsb.st_dev ||
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sb.st_ino != fsb.st_ino) {
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/* changed under our feet */
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close(fd);
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continue;
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}
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return (fd);
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}
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}
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@ -70,6 +70,7 @@ void clean_environment(const char * const *_white,
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const char * const *_more_white);
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int extattr_namespace_to_string(int _attrnamespace, char **_string);
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int extattr_string_to_namespace(const char *_string, int *_attrnamespace);
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int flopen(const char *_path, int _flags, mode_t _mode);
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void login(struct utmp *_ut);
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int login_tty(int _fd);
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int logout(const char *_line);
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