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Technical Reference: Communications, Volume 2
t_open Subroutine for X/Open Transport Interface
Purpose
Establish a transport endpoint.
Library
X/Open Transport Interface Library (libxti.a)
Syntax
#include <xti.h>
#include <fcntl.h>
int t_open (
const char *name;
int oflag;
struct t_info *info)
Description
The t_open subroutine must be
called as the first step in the initialization of a transport endpoint. This
subroutine establishes a transport endpoint by supplying a transport provider
identifier that indicates a particular transport provider (for example, transport
protocol) and returning a file descriptor that identifies that endpoint.
This subroutine also returns various default characteristics
of the underlying transport protocol by setting fields in the t_info structure.
Parameters
name |
Points to a transport provider identifier. |
oflag |
Identifies any open flags (as in the open exec)
. The oflag parameter is constructed from O_RDWR optionally bitwise inclusive-OR-ed with O_NONBLOCK. These flags are defined by the fcntl.h header
file. The file descriptor returned by the t_open subroutine
is used by all subsequent subroutines to identify the particular local transport
endpoint. |
info |
Points to a t_info structure which contains
the following members:
long addr; /* max size of the transport protocol */
/* address */
long options; /* max number of bytes of */
/* protocol-specific options */
long tsdu; /* max size of a transport service data */
/* unit (TSDU) */
long etsdu; /* max size of an expedited transport */
/* service data unit (ETSDU) */
long connect; /* max amount of data allowed on */
/* connection establishment subroutines */
long discon; /* max amount of data allowed on */
/* t_snddis and t_rcvdis subroutines */
long servtype; /* service type supported by the */
/* transport provider */
long flags; /* other info about the transport provider */
The values of the fields have the following meanings:
- addr
- A value greater than zero indicates the maximum size of a transport
protocol address and a value of -2 specifies that the transport provider does
not provide user access to transport protocol addresses.
- options
- A value greater than zero indicates the maximum number of bytes of
protocol-specific options supported by the provider, 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. Note that the semantics of expedited
data may be quite different for different transport providers.
- connect
- A value greater than zero specifies the maximum amount of data that
may be associated with connection establishment subroutines and a value of
-2 specifies that the transport provider does not allow data to be sent with
connection establishment subroutines.
- discon
- A value greater than zero specifies the maximum amount of data that
may be associated with the t_synddis and t_rcvdis subroutines and a value of -2 specifies that the transport provider
does not allow data to be sent with the abortive release subroutines.
|
|
- servtype
- This field specifies the service type supported by the transport provider.
The valid values on return are:
- 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.
- flags
- 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 the underlying transport provider supports the sending of zero-length
TSDUs.
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 subroutine may be used to allocate these buffers. An error will
result if a transport user exceeds the allowed data size on any subroutine.
If the info parameter
is set to a null pointer by the transport user, no protocol information is
returned by the t_open subroutine. |
Valid States
T_UNINIT
Return Values
Valid file descriptor |
Successful completion. |
-1 |
t_errno is set to indicate an error. |
Error Codes
On failure, t_errno is set to
one of the following:
Value |
Description |
TBADFLAG |
An invalid flag is specified. |
TBADNAME |
Invalid transport provider name. |
TSYSERR |
A system error has occurred during execution of this subroutine. |
TPROTO |
This error indicates that a communication problem has been detected
between the X/Open Transport Interface and the transport provider for which there is no
other suitable X/Open Transport Interface (t_errno). |
Related Information
The t_open subroutine.
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