path: root/mcon/U/nblock_io.U

?RCS: $Id$
?RCS:
?RCS: Copyright (c) 1991-1997, 2004-2006, Raphael Manfredi
?RCS: 
?RCS: You may redistribute only under the terms of the Artistic Licence,
?RCS: as specified in the README file that comes with the distribution.
?RCS: You may reuse parts of this distribution only within the terms of
?RCS: that same Artistic Licence; a copy of which may be found at the root
?RCS: of the source tree for dist 4.0.
?RCS:
?RCS: $Log: nblock_io.U,v $
?RCS: Revision 3.0.1.2  1997/02/28  16:17:14  ram
?RCS: patch61: simplify here document for shells that can't handle them well
?RCS: patch61: force use of "startsh" at the head of the generated script
?RCS: patch61: added new files to the ?F: metalint hint
?RCS:
?RCS: Revision 3.0.1.1  1995/07/25  14:13:22  ram
?RCS: patch56: created
?RCS:
?X:
?X: Simplify here document for shells that can't handle them well.
?X: (Problem reported on FreeBSD; it's unclear if this helps.)  --AD
?X:
?MAKE:o_nonblock eagain rd_nodata d_eofnblk: cat rm +cc +ccflags +ldflags \
	d_open3 h_sysfile h_fcntl signal_t hint Oldconfig Setvar startsh Warn
?MAKE:	-pick add $@ %<
?S:o_nonblock:
?S:	This variable bears the symbol value to be used during open() or fcntl()
?S:	to turn on non-blocking I/O for a file descriptor. If you wish to switch
?S:	between blocking and non-blocking, you may try ioctl(FIOSNBIO) instead,
?S:	but that is only supported by some devices.
?S:.
?S:eagain:
?S:	This variable bears the symbolic errno code set by read() when no
?S:	data is present on the file and non-blocking I/O was enabled (otherwise,
?S:	read() blocks naturally).
?S:.
?S:rd_nodata:
?S:	This variable holds the return code from read() when no data is
?S:	present. It should be -1, but some systems return 0 when O_NDELAY is
?S:	used, which is a shame because you cannot make the difference between
?S:	no data and an EOF.. Sigh!
?S:.
?S:d_eofnblk:
?S:	This variable conditionally defines EOF_NONBLOCK if EOF can be seen
?S:	when reading from a non-blocking I/O source.
?S:.
?C:VAL_O_NONBLOCK:
?C:	This symbol is to be used during open() or fcntl(F_SETFL) to turn on
?C:	non-blocking I/O for the file descriptor. Note that there is no way
?C:	back, i.e. you cannot turn it blocking again this way. If you wish to
?C:	alternatively switch between blocking and non-blocking, use the
?C:	ioctl(FIOSNBIO) call instead, but that is not supported by all devices.
?C:.
?C:VAL_EAGAIN:
?C:	This symbol holds the errno error code set by read() when no data was
?C:	present on the non-blocking file descriptor.
?C:.
?C:RD_NODATA:
?C:	This symbol holds the return code from read() when no data is present
?C:	on the non-blocking file descriptor. Be careful! If EOF_NONBLOCK is
?C:	not defined, then you can't distinguish between no data and EOF by
?C:	issuing a read(). You'll have to find another way to tell for sure!
?C:.
?C:EOF_NONBLOCK:
?C:	This symbol, if defined, indicates to the C program that a read() on
?C:	a non-blocking file descriptor will return 0 on EOF, and not the value
?C:	held in RD_NODATA (-1 usually, in that case!).
?C:.
?H:#define VAL_O_NONBLOCK $o_nonblock
?H:#define VAL_EAGAIN $eagain
?H:#define RD_NODATA $rd_nodata
?H:#$d_eofnblk EOF_NONBLOCK
?H:.
?F:!try !try.out !try.ret !try.err !mtry
?T:status
?LINT:use d_open3
: check for non-blocking I/O stuff
case "$h_sysfile" in
true) echo "#include <sys/file.h>" > head.c;;
*)
	case "$h_fcntl" in
	true) echo "#include <fcntl.h>" > head.c;;
	*) echo "#include <sys/fcntl.h>" > head.c;;
	esac
	;;
esac
echo " "
echo "Figuring out the flag used by open() for non-blocking I/O..." >&4
case "$o_nonblock" in
'')
	$cat head.c > try.c
	$cat >>try.c <<'EOCP'
int main() {
#ifdef O_NONBLOCK
	printf("O_NONBLOCK\n");
	exit(0);
#endif
#ifdef O_NDELAY
	printf("O_NDELAY\n");
	exit(0);
#endif
?X: Stevens "Advanced Programming in the UNIX Environment" page 364 mentions
?X: the FNDELAY symbol, used in 4.33BSD (source: Paul Marquess).
#ifdef FNDELAY
	printf("FNDELAY\n");
	exit(0);
#endif
	exit(0);
}
EOCP
	if $cc $ccflags $ldflags -o try try.c >/dev/null 2>&1; then
		o_nonblock=`./try`
		case "$o_nonblock" in
		'') echo "I can't figure it out, assuming O_NONBLOCK will do.";;
		*) echo "Seems like we can use $o_nonblock.";;
		esac
	else
		echo "(I can't compile the test program; pray O_NONBLOCK is right!)"
	fi
	;;
*) echo "Using $hint value $o_nonblock.";;
esac
$rm -f try try.* .out core

echo " "
echo "Let's see what value errno gets from read() on a $o_nonblock file..." >&4
case "$eagain" in
'')
	$cat head.c > try.c
	$cat >>try.c <<EOCP
#include <errno.h>
#include <sys/types.h>
#include <signal.h>
#define MY_O_NONBLOCK $o_nonblock
extern int errno;
$signal_t blech(x) int x; { exit(3); }
EOCP
	$cat >> try.c <<'EOCP'
int main()
{
	int pd[2];
	int pu[2];
	char buf[1];
	char string[100];

	pipe(pd);	/* Down: child -> parent */
	pipe(pu);	/* Up: parent -> child */
	if (0 != fork()) {
		int ret;
		close(pd[1]);	/* Parent reads from pd[0] */
		close(pu[0]);	/* Parent writes (blocking) to pu[1] */
		if (-1 == fcntl(pd[0], F_SETFL, MY_O_NONBLOCK))
			exit(1);
		signal(SIGALRM, blech);
		alarm(5);
		if ((ret = read(pd[0], buf, 1)) > 0)	/* Nothing to read! */
			exit(2);
		sprintf(string, "%d\n", ret);
		write(2, string, strlen(string));
		alarm(0);
#ifdef EAGAIN
		if (errno == EAGAIN) {
			printf("EAGAIN\n");
			goto ok;
		}
#endif
#ifdef EWOULDBLOCK
		if (errno == EWOULDBLOCK)
			printf("EWOULDBLOCK\n");
#endif
	ok:
		write(pu[1], buf, 1);	/* Unblocks child, tell it to close our pipe */
		sleep(2);				/* Give it time to close our pipe */
		alarm(5);
		ret = read(pd[0], buf, 1);	/* Should read EOF */
		alarm(0);
		sprintf(string, "%d\n", ret);
		write(3, string, strlen(string));
		exit(0);
	}

	close(pd[0]);			/* We write to pd[1] */
	close(pu[1]);			/* We read from pu[0] */
	read(pu[0], buf, 1);	/* Wait for parent to signal us we may continue */
	close(pd[1]);			/* Pipe pd is now fully closed! */
	exit(0);				/* Bye bye, thank you for playing! */
}
EOCP
	if $cc $ccflags $ldflags -o try try.c >/dev/null 2>&1; then
?X: Use script to avoid the possible 'alarm call' message
		echo "$startsh" >mtry
		echo "./try >try.out 2>try.ret 3>try.err || exit 4" >>mtry
		chmod +x mtry
		./mtry >/dev/null 2>&1
		case $? in
		0) eagain=`$cat try.out`;;
		1) echo "Could not perform non-blocking setting!";;
		2) echo "I did a successful read() for something that was not there!";;
		3) echo "Hmm... non-blocking I/O does not seem to be working!";;
		*) echo "Something terribly wrong happened during testing.";;
		esac
		rd_nodata=`$cat try.ret`
		echo "A read() system call with no data present returns $rd_nodata."
		case "$rd_nodata" in
		0|-1) ;;
		*)
			echo "(That's peculiar, fixing that to be -1.)"
			rd_nodata=-1
			;;
		esac
		case "$eagain" in
		'')
			echo "Forcing errno EAGAIN on read() with no data available."
			eagain=EAGAIN
			;;
		*)
			echo "Your read() sets errno to $eagain when no data is available."
			;;
		esac
		status=`$cat try.err`
		case "$status" in
		0) echo "And it correctly returns 0 to signal EOF.";;
		-1) echo "But it also returns -1 to signal EOF, so be careful!";;
		*) echo "However, your read() returns '$status' on EOF??";;
		esac
		val="$define"
		if test "$status" = "$rd_nodata"; then
			./warn "your read() can't distinguish between EOF and no data!"
			val="$undef"
		fi
	else
		echo "I can't compile the test program--assuming errno EAGAIN will do."
		eagain=EAGAIN
	fi
	set d_eofnblk
	eval $setvar
	;;
*)
	echo "Using $hint value $eagain."
	echo "Your read() returns $rd_nodata when no data is present."
	case "$d_eofnblk" in
	"$define") echo "And you can see EOF because read() returns 0.";;
	"$undef") echo "But you can't see EOF status from read() returned value.";;
	*)
?X: Should not happen, but if it does, assume the worst!
		echo "(Assuming you can't see EOF status from read anyway.)"
		d_eofnblk=$undef
		;;
	esac
	;;
esac
$rm -f try try.* .out core head.c mtry