Problems with open() and close()

3 Aug 2006


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Thanks for any help,
Cem Karan
boolean_t open_TTY_OSX(char *devicePath, OSX_TTYcontext context)
{
    size_t counter;
    adjAssert((devicePath != NULL) && (context != NULL));
    if ((devicePath == NULL) || (context == NULL))
        return false;
    if (ioctl(context->fileDescriptor, TIOCEXCL) == -1) {
        ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);
        return false;
    }
    if (fcntl(context->fileDescriptor, F_SETFL, 0) == -1) {
        ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);
        return false;
    }
    if (fcntl(context->fileDescriptor, F_NOCACHE, 1) == -1) {
        ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);
        return false;
    }
    for (counter = 0; counter < NCCS; counter++)
        (context->current).c_cc[counter] = _POSIX_VDISABLE;
    cfmakeraw(&(context->current));
    (context->current).c_cc[VMIN]   = 1;
    (context->current).c_cc[VTIME]  = 1;
    cfsetspeed(&(context->current), B57600); 	/* Set 57600 baud */
    (context->current).c_cflag |= (CS8 | CREAD | CLOCAL);
    return true;
}
void close_TTY_OSX(OSX_TTYcontext context)
{
    int result;
    adjAssert(context != NULL);
    if (tcdrain(context->fileDescriptor) == -1) {
        printf("Error waiting for drain - %s(%d).\n",
            strerror(errno), errno);
    }
    if (ioctl(context->fileDescriptor, TIOCNXCL) == -1) {
        ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);
    }
    result = close(context->fileDescriptor);
    if (result != 0)
        perror(NULL);
}
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Hi all, first time poster to this list, hope that this is right list
to post to...
I've adapted some code to my own uses (shown below) but have run into
an odd problem, and I'm hoping that someone can explain what is going
on to me.  As a part of my open_TTY_OSX() function, I call ioctl
(context->fileDescriptor, TIOCEXCL), which prevents any non-root
program from opening the same device.  Now this is where it gets odd
for me.  I am testing all this code using some unit tests that I
wrote.  The unit tests call open_TTY_OSX() and then balance the call
with a call to close_TTY_OSX() on the same file descriptor.
Originally, I did NOT have the ioctl(context->fileDescriptor,
TIOCNXCL) call in close_TTY_OSX(), and the result was that if I tried
to open the same device again, it would fail with EBUSY.  So basically:


	open_TTY_OSX("/dev/ttyp1", foo) // no problem

	close_TTY_OSX(foo)		// no problem

	open_TTY_OSX("/dev/ttyp1, bar)	// Fails with EBUSY
Well, I figured that this isn't that big a deal, I just let my
process exit nicely, and the restart the debugging session, right?
No good.  The only way for me to make things play nice is to quit
XCode, and even that doesn't seem to work 100% of the time.  My
question is why?  When I close, I reset the attributes, and I close()
the descriptor.  That should make the blocking part go away, right?
What am I doing wrong?
Oh, note that adjAssert() is a macro like assert(); I just hacked in
some extra stuff that I needed, and didn't what the names conflicting.

#define ERROR_CLOSE_FD_TTY_OSX_PRIVATE
(FD)                                  \

{
    \

    struct stat
myStat;                                                     \

    perror
(NULL);                                                           \

    fflush
(stderr);                                                         \

    fflush
(stdout);                                                         \

    if (FD !=
-1)                                                           \


{
\

        printf("Closing file
descriptor");                                  \

        fstat(FD,
&myStat);                                                 \

        close
(FD);                                                          \

    }
     \

}
    context->fileDescriptor = open(devicePath, O_RDWR | O_NOCTTY |
O_NONBLOCK);

    if (context->fileDescriptor == -1){

        ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);

        return false;

    }
    if (tcgetattr(context->fileDescriptor, &(context->original)) ==
-1) {

        printf("Error getting tty attributes %s - %s(%d).\n",

            devicePath, strerror(errno), errno);

        ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);

        return false;

    }
    memcpy(&(context->current), &(context->original), sizeof(struct
termios));
    if (tcsetattr(context->fileDescriptor, TCSANOW, &(context-
...
current)) == -1) {
ERROR_CLOSE_FD_TTY_OSX_PRIVATE(context->fileDescriptor);

        return false;

    }
    if (tcsetattr(context->fileDescriptor, TCSANOW, &(context-
...
original)) == -1) {
printf("Error resetting tty attributes - %s(%d).\n",

            strerror(errno), errno);

    }
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