t_alloc(NET)

t_alloc -- allocate a library data structure

Synopsis

cc [options] file -lnsl

#include <xti.h>

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

Description

The t_alloc function is an TLI/XTI local management routine used to allocate data structures associated with the endpoint specified by fd. For struct_type T_INFO, fd is ignored, so that T_INFO structures may be allocated for use in calls to t_open.

t_alloc 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 can be one of the following:

   T_BIND          /* struct t_bind        */
   T_OPTMGMT       /* struct t_optmgmt     */
   T_CALL          /* struct t_call        */
   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.

Parameters

fd: the file descriptor for the transport endpoint.
struct_type: identifies the type of structure for which memory should be allocated.
fields: indicates fields for which buffers should be allocated.

Structure definitions

Each of the above structures, except T_INFO, contains at least one field of type struct netbuf. netbuf is described in intro(NET). 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 or t_getinfo. 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 field specified in fields, t_alloc will allocate memory for the buffer associated with the field, initialize the len field to 0 and initialize the buf pointer and maxlen (see netbuf in intro(NET) for description of buf and maxlen) field accordingly. The length of the buffer allocated will be based on the same size information that is returned to the user on t_open and t_getinfo. Thus, fd must refer to the transport endpoint through which the newly allocated structure will be passed, so that the appropriate size information can be accessed.

If the size value associated with any specified field is -1, or -2, t_alloc will be unable to determine the size of the buffer to allocate and will fail with t_errno set to TSYSERR, unless when T_ALL is specified, in which case unsupported fields are ignored silently.

For any field not specified in fields, buf will be set to NULL and maxlen will be set to 0. If the fields argument is set to T_ALL, fields that are not supported by the transport provider specified by fd are not allocated.

State transitions

t_alloc has no effect on state. Valid states are T_UNBND, T_IDLE, T_OUTCON, T_INCON, T_DATAXFER, T_OUTREL and T_INREL on entry. On exit, they are unchanged.

Files

/usr/lib/libxti.so: X/Open^® Transport Interface Library (shared object)
/usr/lib/libnsl.so: Network Services Library (shared object)

Return values

On successful completion, t_alloc returns a pointer to the newly allocated structure. On failure, NULL is returned, and t_errno is set to indicate the error.

Errors

On failure, t_errno may be set to one of the following:

TBADF: The specified file descriptor does not refer to a transport endpoint.
TSYSERR: A system error has occurred during execution of this function.
TNOSTRUCTYPE: The argument that specifies struct_type is invalid, for example, because the type of structure requested is inconsistent with the transport provider (connection mode or connectionless) indicated by fd.
TPROTO: A communication problem has been detected with the transport provider and there is no other value of t_errno to describe the error condition.

References

intro(NET), t_free(NET), t_getinfo(NET), t_open(NET)

Notices

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

Buffers and memory that have been allocated with t_alloc may be freed with t_free.