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


See attributes(5) for descriptions of the following attributes:


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT Level | Safe |
+---------------+-----------------+

SEE ALSO


free(3C), malloc(3C), t_connect(3NSL), t_free(3NSL), t_getinfo(3NSL),
t_open(3NSL), attributes(5)


May 7, 1998 T_ALLOC(3NSL)