The t_open(3) function must be called as the first step
in the initialisation of a transport endpoint. This function
establishes a transport endpoint by supplying a transport provider
identifier that indicates a particular transport provider (that is,
transport protocol) and returning a file descriptor that identifies
that endpoint.
Parameters
Before call
After call
namex
x
=
oflag
x
=
info->
addr
/
info->
options
/
info->
tsdu
/
info->
etsdu
/
info->
connect
/
info->
discon
/
info->
servtype
/
info->
flags
/
The argument name points to a transport provider
identifier and oflag identifies any open flags (as in
open(3)).
The argument oflag is constructed from O_RDWR optionally bitwise
inclusive-OR'ed with O_NONBLOCK. These flags are defined by the
header <fcntl.h>. The file descriptor returned by
t_open() will be used by all subsequent functions to
identify the particular local transport endpoint.
This function also returns various default characteristics of
the underlying transport protocol by setting fields in the t_info
structure. This argument points to a t_info which contains the
following members:
t_scalar_t addr; /* max size of the transport protocol address */
t_scalar_t options; /* max number of bytes of */
/* protocol-specific options */
t_scalar_t tsdu; /* max size of a transport service data */
/* unit (TSDU) */
t_scalar_t etsdu; /* max size of an expedited transport */
/* service data unit (ETSDU) */
t_scalar_t connect; /* max amount of data allowed on */
/* connection establishment functions */
t_scalar_t discon; /* max amount of data allowed on */
/* t_snddis() and t_rcvdis() functions */
t_scalar_t servtype; /* service type supported by the */
/* transport provider */
t_scalar_t flags; /* other info about the transport provider */
The values of the fields have the following meanings:
addr
A value greater than zero (T_NULL) indicates the maximum size
of a transport protocol address and a value of -2 (T_INVALID)
specifies that the transport provider does not provide user access
to transport protocol addresses.
options
A value greater than zero (T_NULL) indicates the maximum number
of bytes of protocol-specific options supported by the provider,
and a value of -2 (T_INVALID) specifies that the transport provider
does not support user-settable options.
tsdu
A value greater than zero (T_NULL) specifies the maximum size
of a transport service data unit (TSDU); a value of zero (T_NULL)
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
(T_INFINITE) specifies that there is no limit to the size of a
TSDU; and a value of -2 (T_INVALID) specifies that the transfer of
normal data is not supported by the transport provider.
etsdu
A value greater than zero (T_NULL) specifies the maximum size
of an expedited transport service data unit (ETSDU); a value of
zero (T_NULL) 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 (T_INFINITE) specifies that
there is no limit on the size of an ETSDU; and a value of -2
(T_INVALID) 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 (see and ).
connect
A value greater than zero (T_NULL) specifies the maximum amount
of data that may be associated with connection establishment
functions, and a value of -2 (T_INVALID) specifies that the
transport provider does not allow data to be sent with connection
establishment functions.
discon
If the T_ORDRELDATA bit in flags is clear, a value greater than
zero (T_NULL) specifies the maximum amount of data that may be
associated with the t_snddis(3) and t_rcvdis(3) functions, and a
value of -2 (T_INVALID) specifies that the transport provider does
not allow data to be sent with the abortive release functions. If
the T_ORDRELDATA bit is set in flags, a value greater than zero
(T_NULL) specifies the maximum number of octets that may be
associated with the t_snddis(3) and t_rcvdis(3) functions.
servtype
This field specifies the service type supported by the
transport provider, as described below.
flags
This is a bit field used to specify other information about the
communications provider. If the T_ORDRELDATA bit is set, the
communications provider supports user data to be sent with an
orderly release. If the T_SENDZERO bit is set in flags, this
indicates the underlying transport provider supports the sending of
zero-length TSDUs. See for a discussion of the separate issue of
zero-length fragments within a TSDU.
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(3)
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 specifies 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 (T_INVALID)
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 a null pointer by the transport user, no
protocol information is returned by t_open().
This error indicates that a communication problem has been
detected between XTI and the transport provider for which there is
no other suitable XTI error (t_errno).
[TSYSERR]
A system error has occurred during execution of this
function.