Tribblix: manual page: t

T_ALLOC(3NSL) Networking Services Library Functions T_ALLOC(3NSL)

NAME

t_alloc - allocate a library structure

SYNOPSIS

#include <xti.h>

void *t_alloc(int fd, int struct_type, int fields);

DESCRIPTION

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, a different
header file, tiuser.h, must be used. Refer to the section, TLI
COMPATIBILITY, for a description of differences between the two
interfaces.

The t_alloc() function dynamically allocates memory for the various
transport function argument structures as specified below. This
function will allocate memory for the specified structure, and will
also allocate memory for buffers referenced by the structure.

The structure to allocate is specified by struct_type and must be one
of the following:

T_BIND struct t_bind
T_CALL struct t_call
T_OPTMGMT struct t_optmgmt
T_DIS struct t_discon
T_UNITDATA struct t_unitdata
T_UDERROR struct t_uderr
T_INFO struct t_info

where each of these structures may subsequently be used as an
argument to one or more transport functions.

Each of the above structures, except T_INFO, contains at least one
field of type struct netbuf. For each field of this type, the user
may specify that the buffer for that field should be allocated as
well. The length of the buffer allocated will be equal to or greater
than the appropriate size as returned in the info argument of
t_open(3NSL) or t_getinfo(3NSL). The relevant fields of the info
argument are described in the following list. The fields argument
specifies which buffers to allocate, where the argument is the
bitwise-or of any of the following:

T_ADDR
The addr field of the t_bind, t_call, t_unitdata or
t_uderr structures.

T_OPT
The opt field of the t_optmgmt, t_call, t_unitdata or
t_uderr structures.

T_UDATA
The udata field of the t_call, t_discon or t_unitdata
structures.

T_ALL
All relevant fields of the given structure. Fields which
are not supported by the transport provider specified by
fd will not be allocated.

For each relevant field specified in fields, t_alloc() will allocate
memory for the buffer associated with the field, and initialize the
len field to zero and the buf pointer and maxlen field accordingly.
Irrelevant or unknown values passed in fields are ignored. Since the
length of the buffer allocated will be based on the same size
information that is returned to the user on a call to t_open(3NSL)
and t_getinfo(3NSL), fd must refer to the transport endpoint through
which the newly allocated structure will be passed. In the case where
a T_INFO structure is to be allocated, fd may be set to any value. In
this way the appropriate size information can be accessed. If the
size value associated with any specified field is T_INVALID,
t_alloc() will be unable to determine the size of the buffer to
allocate and will fail, setting t_errno to TSYSERR and errno to
EINVAL. See t_open(3NSL) or t_getinfo(3NSL). If the size value
associated with any specified field is T_INFINITE, then the behavior
of t_alloc() is implementation-defined. For any field not specified
in fields, buf will be set to the null pointer and len and maxlen
will be set to zero. See t_open(3NSL) or t_getinfo(3NSL).

The pointer returned if the allocation succeeds is suitably aligned
so that it can be assigned to a pointer to any type of object and
then used to access such an object or array of such objects in the
space allocated.

Use of t_alloc() to allocate structures will help ensure the
compatibility of user programs with future releases of the transport
interface functions.

RETURN VALUES

On successful completion, t_alloc() returns a pointer to the newly
allocated structure. On failure, a null pointer is returned.

VALID STATES

ALL - apart from T_UNINIT

ERRORS

On failure, t_errno is set to one of the following:

TBADF
struct_type is other than T_INFO and the specified
file descriptor does not refer to a transport
endpoint.

TNOSTRUCTYPE
Unsupported struct_type requested. This can include a
request for a structure type which is inconsistent
with the transport provider type specified, that is,
connection-mode or connectionless-mode.

TPROTO
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.

TLI COMPATIBILITY

The XTI and TLI interface definitions have common names but use
different header files. This, and other semantic differences between
the two interfaces are described in the subsections below.

Interface Header

The XTI interfaces use the header file, xti.h. TLI interfaces should
not use this header. They should use the header:

#include <tiuser.h>

Error Description Values

The t_errno values that can be set by the XTI interface and cannot be
set by the TLI interface are:

TPROTO

TNOSTRUCTYPE

Special Buffer Sizes

Assume that the value associated with any field of struct t_info
(argument returned by t_open() or t_getinfo()) that describes buffer
limits is -1. Then the underlying service provider can support a
buffer of unlimited size. If this is the case, t_alloc() will
allocate a buffer with the default size 1024 bytes, which may be
handled as described in the next paragraph.

If the underlying service provider supports a buffer of unlimited
size in the netbuf structure (see t_connect(3NSL)), t_alloc() will
return a buffer of size 1024 bytes. If a larger size buffer is
required, it will need to be allocated separately using a memory
allocation routine such as malloc(3C). The buf and maxlen fields of
the netbuf data structure can then be updated with the address of the
new buffer and the 1024 byte buffer originally allocated by t_alloc()
can be freed using free(3C).

Assume that the value associated with any field of struct t_info
(argument returned by t_open() or t_getinfo() ) that describes
nbuffer limits is -2. Then t_alloc() will set the buffer pointer to
NULL and the buffer maximum size to 0, and then will return success
(see t_open(3NSL) or t_getinfo(3NSL)).

ATTRIBUTES