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This routine is part of the XTI interfaces which evolved from the TLI interfaces. XTI represents the future evolution of these interfaces. However, TLI interfaces are
supported for compatibility. When using a TLI routine that has the same name as an XTI routine, the tiuser.h header file must be used. Refer to the TLI COMPATIBILITY section for
a description of differences between the two interfaces.
The t_open() function must be called as the first step in the initialization 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.
The argument name points to a transport provider identifier and oflag identifies any open flags, as in open(2).
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:
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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 */
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The values of the fields have the following meanings:
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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.
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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.
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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.
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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.
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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.
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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(3NSL) and t_rcvdis(3NSL) 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_sndreldata(), t_rcvreldata(), t_snddis(3NSL) and t_rcvdis(3NSL) functions.
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servtype
- This field specifies the service type supported by the transport provider, as described below.
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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.
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(3NSL) 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:
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T_COTS
- The transport provider supports a connection-mode service but does not support the optional orderly release facility.
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T_COTS_ORD
- The transport provider supports a connection-mode service with the optional orderly release facility.
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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().
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