t_open(3N)t_open(3N)NAMEt_open - establish a transport endpoint
SYNOPSIS
#ifdef _XOPEN_SOURCE
#include <xti.h>
#else
#include <tiuser.h>
#endif
#include <fcntl.h>
int t_open (char path, int oflag, struct t_info *info);
DESCRIPTIONt_open must be called as the first step in the initialization of a
transport endpoint. This function establishes a transport endpoint by
opening a UNIX file that identifies a particular transport provider (that
is, transport protocol) and returning a file descriptor that identifies
that endpoint. For example, opening the file /dev/iso_cots identifies an
OSI connection-oriented transport layer protocol as the transport
provider.
path points to the path name of the file to open, and oflag identifies
any open flags [as in open(2)]. oflag may be constructed from O_NDELAY
or O_NONBLOCK OR-ed with O_RDWR. These flags are defined in the header
file <fcntl.h>. t_open returns a file descriptor that will be used by
all subsequent functions to identify the particular local transport
endpoint.
t_open also returns various default characteristics of the underlying
transport protocol by setting fields in the t_info structure. The t_info
argument points to a t_info structure that contains the following
members:
long addr;/* maximum size of the transport protocol address */
long options;/* maximum number of bytes of protocol-specific options */
long tsdu;/* maximum size of a transport service data unit (TSDU) */
long etsdu;/* maximum size of an expedited transport service data unit (ETSDU) */
long connect;/* maximum amount of data allowed on connection establishment
functions */
long discon;/* maximum amount of data allowed on t_snddis and t_rcvdis
functions */
long servtype;/* service type supported by the transport provider */
#ifdef _XOPEN_SOURCE
long flags;/* other info about the transport provider */
#endif
The values of the fields have the following meanings:
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t_open(3N)t_open(3N)
addr A value greater than or equal to zero indicates the maximum
size of a transport protocol address; a value of -1
specifies that there is no limit on the address size; and a
value of -2 specifies that the transport provider does not
provide user access to transport protocol addresses.
options A value greater than or equal to zero indicates the maximum
number of bytes of protocol-specific options supported by
the provider; a value of -1 specifies that there is no
limit on the option size; and a value of -2 specifies that
the transport provider does not support user-settable
options.
tsdu A value greater than zero specifies the maximum size of a
transport service data unit (TSDU); a value of zero
specifies that the transport provider does not support the
concept of TSDU, although it does support the sending of a
data stream with no logical boundaries preserved across a
connection; a value of -1 specifies that there is no limit
on the size of a TSDU; and a value of -2 specifies that the
transfer of normal data is not supported by the transport
provider.
etsdu A value greater than zero specifies the maximum size of an
expedited transport service data unit (ETSDU); a value of
zero specifies that the transport provider does not support
the concept of ETSDU, although it does support the sending
of an expedited data stream with no logical boundaries
preserved across a connection; a value of -1 specifies that
there is no limit on the size of an ETSDU; and a value of
-2 specifies that the transfer of expedited data is not
supported by the transport provider.
connect A value greater than or equal to zero specifies the maximum
amount of data that may be associated with connection
establishment functions; a value of -1 specifies that there
is no limit on the amount of data sent during connection
establishment; and a value of -2 specifies that the
transport provider does not allow data to be sent with
connection establishment functions.
discon A value greater than or equal to zero specifies the maximum
amount of data that may be associated with the t_snddis and
t_rcvdis functions; a value of -1 specifies that there is
no limit on the amount of data sent with these abortive
release functions; and a value of -2 specifies that the
transport provider does not allow data to be sent with the
abortive release functions.
servtype This field specifies the service type supported by the
transport provider, as described below.
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t_open(3N)t_open(3N)
flags If _XOPEN_SOURCE is defined, then this structure element
will exist. This is a bit field used to specify other
information about the transport provider. If the
T_SENDZERO bit is set in flags, this indicates that the
underlying transport provider supports the sending of
zero-length TSDUs. Following is a dicussion of the
separate issue of zero-length fragments within a TSDU.
Sending data of zero octets:
The transport service definition, both in connection-
oriented mode and in connectionless mode, does not permit
sending a TSDU of zero octets. So, in connectionless mode,
if the len parameter is set to zero, the t_sndudata() call
will always return unsuccessfully with -1 and t_errno set
to TBADDATA. In connection-oriented mode, if the nbytes
parameter is set to zero, the t_snd() call will return with
-1 and t_errno set to TBADDATA if either the T_MORE flag is
set or the T_MORE flag is not set and the preceding t_snd()
call completed a TSDU or ETSDU (that is, the call has
requested sending a zero byte TSDU or ETSDU.
If a transport user is concerned with protocol independence, the above
sizes may be accessed to determine how large the buffers must be to hold
each piece of information. Alternatively, the t_alloc function may be
used to allocate these buffers. An error will result if a transport user
exceeds the allowed data size on any function.
The servtype field of info may specify one of the following values on
return:
T_COTS The transport provider supports a connection-mode service
but does not support the optional orderly release facility.
T_COTS_ORD The transport provider supports a connection-mode service
with the optional orderly release facility.
T_CLTS The transport provider supports a connectionless-mode
service. For this service type, t_open will return -2 for
etsdu, connect, and discon.
A single transport endpoint may support only one of the above services at
one time.
If info is set to NULL by the transport user, no protocol information is
returned by t_open.
This function resides within both the X/Open compliant libxnet and the
SVR4 compliant libnsl Network Services libraries. Network Services
applications which require X/Open compliance must link-load with -lxnet.
Network Services applications which require SVR4 compliance must link-
load with -lnsl.
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t_open(3N)t_open(3N)
On failure, t_errno may be set to the following:
TSYSERR A system error has occurred during execution of this
function.
TBADFLAG An invalid flag is specified.
TBADNAME If _XOPEN_SOURCE is defined, then when an invalid
transport provider name is encountered, this value is
returned within t_errno.
DIAGNOSTICSt_open returns a valid file descriptor on success and -1 on failure and
t_errno is set to indicate the error.
NOTES
If t_open is used on a non-TLI-conforming STREAMS device, unpredictable
events may occur.
SEE ALSOopen(2)
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