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_UNINITERRORS
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(7) 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(7) May 7, 1998
T_ALLOC(3NSL)