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Open the file descriptor of a serial port on POSIX systems exclusively

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This fixes bug #1510.
This commit is contained in:
Leon Varga 2020-03-03 14:18:53 +01:00 committed by Uwe Hermann
parent 0a24247de8
commit ffbfc5c76b
3 changed files with 40 additions and 0 deletions
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4
configure.ac
View File

@ -129,6 +129,10 @@ AC_CHECK_TYPES([struct serial_struct],,, [[#include <linux/serial.h>]])
# Check for realpath().
AC_CHECK_FUNC([realpath], [AC_DEFINE(HAVE_REALPATH, 1, [realpath is available.])], [])
# Check for flock().
AC_CHECK_HEADER([sys/file.h], [AC_DEFINE(HAVE_SYS_FILE_H, 1, [sys/file.h is available.])], [])
AC_CHECK_FUNC([flock], [AC_DEFINE(HAVE_FLOCK, 1, [flock is available.])], [])
# Check for clock_gettime().
AC_CHECK_FUNC([clock_gettime],
[AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [clock_gettime is available.])], [])

3
libserialport_internal.h
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@ -82,6 +82,9 @@
#include <time.h>
#include <poll.h>
#include <unistd.h>
#ifdef HAVE_SYS_FILE_H
#include <sys/file.h>
#endif
#endif
#ifdef __APPLE__
#include <CoreFoundation/CoreFoundation.h>

33
serialport.c
View File

@ -551,6 +551,39 @@ SP_API enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
if ((port->fd = open(port->name, flags_local)) < 0)
RETURN_FAIL("open() failed");
/*
* On POSIX in the default case the file descriptor of a serial port
* is not opened exclusively. Therefore the settings of a port are
* overwritten if the serial port is opened a second time. Windows
* opens all serial ports exclusively.
* So the idea is to open the serial ports alike in the exclusive mode.
*
* ioctl(*, TIOCEXCL) defines the file descriptor as exclusive. So all
* further open calls on the serial port will fail.
*
* There is a race condition if two processes open the same serial
* port. None of the processes will notice the exclusive ownership of
* the other process because ioctl() doesn't return an error code if
* the file descriptor is already marked as exclusive.
* This can be solved with flock(). It returns an error if the file
* descriptor is already locked by another process.
*/
#ifdef HAVE_FLOCK
if (flock(port->fd, LOCK_EX | LOCK_NB) < 0)
RETURN_FAIL("flock() failed");
#endif
#ifdef TIOCEXCL
/*
* Before Linux 3.8 ioctl(*, TIOCEXCL) was not implemented and could
* lead to EINVAL or ENOTTY.
* These errors aren't fatal and can be ignored.
*/
if (ioctl(port->fd, TIOCEXCL) < 0 && errno != EINVAL && errno != ENOTTY)
RETURN_FAIL("ioctl() failed");
#endif
#endif
ret = get_config(port, &data, &config);