t_alloc - allocate a library structure
#include <xti.h> void *t_alloc( int fd, int struct_type, int fields)
Parameters Before call After call fd x / struct_type x / fields x /
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() 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:
- The addr field of the t_bind, t_call, t_unitdata or t_uderr structures.
- The opt field of the t_optmgmt, t_call, t_unitdata or t_uderr structures.
- The udata field of the t_call, t_discon or t_unitdata structures.
- 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 initialise 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() and t_getinfo(), 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 (see t_open() or t_getinfo()), 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]. If the size value associated with any specified field is T_INFINITE (see t_open() or t_getinfo()), then the behaviour 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.
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.
ALL - apart from T_UNINIT
On failure, t_errno is set to one of the following:
- struct_type is other than T_INFO and the specified file descriptor does not refer to a transport endpoint.
- 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.
- 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).
- A system error has occurred during execution of this function.
On successful completion, t_alloc() returns a pointer to the newly allocated structure. On failure, a null pointer is returned.
t_free(), t_getinfo(), t_open().