OpenVMS System Services Reference Manual

Document revision date: 15 July 2002

OpenVMS System Services Reference Manual

Contents

Index

%%%%%%%%%%% OPCOM 30-DEC-2001 13:44:40.37 Operator _NODE$LTA5: has been enabled, username HOEBLE

The following example shows the message displayed on an operator terminal as a result of a request to display the status of that operator terminal:

%%%%%%%%%%% OPCOM 30-DEC-2001 12:11:10.48 Operator status for operator _NODE$OPA0: CENTRAL, PRINTER, TAPES, DISKS, DEVICES, CARDS, CLUSTER, SECURITY, OPER1, OPER2, OPER3, OPER4, OPER5, OPER6, OPER7, OPER8, OPER9, OPER10, OPER11, OPER12

The following example shows the message displayed on an operator terminal as a result of a user request:

%%%%%%%%%%% OPCOM 30-DEC-2001 12:57:32.25 Request 1285, from user ROSS on NODE_NAME Please mount device _NODE$DMA0:

Required Access or Privileges

OPER privilege is required for the following functions:

Enabling a terminal as an operator's terminal
Replying to or canceling a user's request
Initializing the operator communication log file

In addition, the operator must have SECURITY privilege to affect security functions.

Required Quota

None

Related Services

$ALLOC, $ASSIGN, $BRKTHRU, $BRKTHRUW, $CANCEL, $CREMBX, $DALLOC, $DASSGN, $DELMBX, $DEVICE_SCAN, $DISMOU, $GETDVI, $GETDVIW, $GETMSG, $GETQUI, $GETQUIW, $INIT_VOL, $MOUNT, $PUTMSG, $QIO, $QIOW, $SNDERR, $SNDJBC, $SNDJBCW

Condition Values Returned

SS$_NORMAL The service completed successfully.

SS$_ACCVIO The message buffer or buffer descriptor cannot be read by the caller.

SS$_BADPARAM The specified message has a length of 0 or has more than 986 bytes.

SS$_DEVNOTMBX The channel specified is not assigned to a mailbox.

SS$_INSFMEM The service was called from kernel mode or the system dynamic memory is insufficient for completing the service.

SS$_IVCHAN You specified an invalid channel number. An invalid channel number is one that is 0 or a number larger than the number of channels available.

SS$_MBFULL The mailbox used to support communication is full. Retry at a later time.

OPC$_NOPERATOR The service completed successfully; the Operator Communications Manager (OPCOM) is not running and the message will not be sent. Note that OPC$_NOPERATOR is a success status and must be tested for explicitly.

SS$_NOPRIV The process does not have the privilege to reply to or cancel a user's request; the process does not have read/write access to the specified mailbox; or the channel was assigned from a more privileged access mode.

Condition Values Returned in the Mailbox

OPC$_BLANKTAPE The service completed successfully; the operator responded with the DCL command REPLY/BLANK_TAPE=n.

OPC$_INITAPE The service completed successfully; the operator responded with the DCL command REPLY/INITIALIZE_TAPE=n.

OPC$_NOPERATOR The service completed successfully; no operator terminal was enabled to receive the message.

OPC$_RQSTCMPLTE The service completed successfully; the operator completed the request.

OPC$_RQSTPEND The service completed successfully; the operator will perform the request when possible.

OPC$_RQSTABORT The operator could not satisfy the request.

OPC$_RQSTCAN The caller canceled the request.

Examples

#1
#include <ssdef.h> #include <opcdef.h> #include <string.h> #include <descrip.h> #include <starlet.h> #include <lib$routines.h> char input_buffer[256]; /* Input buffer, if needed / / VMS descriptors: / $DESCRIPTOR(input_desc, input_buffer); $DESCRIPTOR(prompt_desc, "Request> "); struct dsc$descriptor req_desc; main(int argc, char argv[]) { int status, /* Status of system calls / length = 0; / Length of message text / struct OPC request; / Request message buffer / / Check for too many arguments on command line / if (argc > 2) return (SS$_OVRMAXARG); / See if request string present on command line... / if (argc > 1) { / It is. Compute length and copy pointer / length = strlen(argv[1]); input_desc.dsc$a_pointer = argv[1]; } / If no message present, prompt user for message text / while (length == 0) { status = lib$get_input(&input_desc, &prompt_desc, &length); if (status != SS$_NORMAL) return (status); }; if (length > 128) / Limit message length / length = 128; / to 128 characters / / Set up request buffer... / request.opc$b_ms_type = OPC$_RQ_RQST; request.opc$b_ms_target = OPC$M_NM_CENTRL; request.opc$l_ms_rqstid = 0; memcpy(&request.opc$l_ms_text, input_desc.dsc$a_pointer, length); / Set up request buffer descriptor and send message / req_desc.dsc$w_length = length + 8; req_desc.dsc$a_pointer = (char ) &request; return (sys$sndopr(&req_desc, 0)); }

#include <ssdef.h> 
#include <opcdef.h> 
#include <string.h> 
#include <descrip.h> 
#include <starlet.h> 
#include <lib$routines.h> 
 
char    input_buffer[256];      /* Input buffer, if needed */ 
 
/* VMS descriptors: */ 
$DESCRIPTOR(input_desc, input_buffer); 
$DESCRIPTOR(prompt_desc, "Request> "); 
struct dsc$descriptor req_desc; 
 
main(int argc, char *argv[]) 
{ 
    int status,                 /* Status of system calls */ 
        length = 0;             /* Length of message text */ 
    struct OPC request;         /* Request message buffer */ 
 
    /* Check for too many arguments on command line */ 
    if (argc > 2) 
        return (SS$_OVRMAXARG); 
 
    /* See if request string present on command line... */ 
    if (argc > 1) 
    { 
        /* It is.  Compute length and copy pointer */ 
        length = strlen(argv[1]); 
        input_desc.dsc$a_pointer = argv[1]; 
    } 
 
    /* If no message present, prompt user for message text */ 
    while (length == 0) 
    { 
        status = lib$get_input(&input_desc, &prompt_desc, &length); 
        if (status != SS$_NORMAL) 
            return (status); 
    }; 
 
    if (length > 128)           /* Limit message length */ 
        length = 128;           /*    to 128 characters */ 
 
    /* Set up request buffer... */ 
    request.opc$b_ms_type = OPC$_RQ_RQST; 
    request.opc$b_ms_target = OPC$M_NM_CENTRL; 
    request.opc$l_ms_rqstid = 0; 
    memcpy(&request.opc$l_ms_text, input_desc.dsc$a_pointer, length); 
 
    /* Set up request buffer descriptor and send message */ 
    req_desc.dsc$w_length = length + 8; 
    req_desc.dsc$a_pointer = (char *) &request; 
    return (sys$sndopr(&req_desc, 0)); 
}

This example allows you to build an operator request and send the request to the operator.

#2
IMPLICIT NONE ! Symbol definitions INCLUDE '($DVIDEF)' INCLUDE '($OPCDEF)' ! Structures for SNDOPR STRUCTURE /MESSAGE/ UNION MAP BYTE TYPE, 2 ENABLE(3) INTEGER4 MASK INTEGER2 OUNIT CHARACTER14 ONAME END MAP MAP CHARACTER24 STRING END MAP END UNION END STRUCTURE RECORD /MESSAGE/ MSGBUF ! Length of MSGBUF.ONAME INTEGER4 ONAME_LEN ! Status and routines INTEGER4 STATUS, 2 LIB$GETDVI, 2 SYS$SNDOPR ! Type MSGBUF.TYPE = OPC$_RQ_TERME ! Enable MSGBUF.ENABLE(1) = 1 ! Operator type MSGBUF.MASK = OPC$M_NM_OPER1 ! Terminal unit number STATUS = LIB$GETDVI (DVI$_UNIT, 2 , 2 'SYS$OUTPUT', 2 MSGBUF.OUNIT,,) IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS)) ! Terminal name STATUS = LIB$GETDVI (DVI$_FULLDEVNAM, 2 , 2 'SYS$OUTPUT',, 2 MSGBUF.ONAME, 2 ONAME_LEN) IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS)) ! Remove unit number from ONAME and set up counted string ONAME_LEN = ONAME_LEN - 3 MSGBUF.ONAME(2:ONAME_LEN+1) = MSGBUF.ONAME(1:ONAME_LEN) MSGBUF.ONAME(1:1) = CHAR(ONAME_LEN) ! Call $SNDOPR STATUS = SYS$SNDOPR (MSGBUF.STRING,) IF (.NOT. STATUS) CALL LIB$SIGNAL(%VAL(STATUS)) END

IMPLICIT NONE 
 
        ! Symbol definitions 
        INCLUDE '($DVIDEF)' 
        INCLUDE '($OPCDEF)' 
 
        ! Structures for SNDOPR 
        STRUCTURE /MESSAGE/ 
         UNION 
          MAP 
           BYTE TYPE, 
        2       ENABLE(3) 
           INTEGER*4 MASK 
           INTEGER*2 OUNIT 
           CHARACTER*14 ONAME 
          END MAP 
          MAP 
           CHARACTER*24 STRING 
          END MAP 
         END UNION 
        END STRUCTURE 
        RECORD /MESSAGE/ MSGBUF 
        ! Length of MSGBUF.ONAME 
        INTEGER*4 ONAME_LEN 
 
        ! Status and routines 
        INTEGER*4 STATUS, 
        2         LIB$GETDVI, 
        2         SYS$SNDOPR 
 
        ! Type 
        MSGBUF.TYPE = OPC$_RQ_TERME 
        ! Enable 
        MSGBUF.ENABLE(1) = 1 
        ! Operator type 
        MSGBUF.MASK = OPC$M_NM_OPER1 
        ! Terminal unit number 
        STATUS = LIB$GETDVI (DVI$_UNIT, 
        2                    , 
        2                    'SYS$OUTPUT', 
        2                    MSGBUF.OUNIT,,) 
        IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS)) 
        ! Terminal name 
        STATUS = LIB$GETDVI (DVI$_FULLDEVNAM, 
        2                    , 
        2                    'SYS$OUTPUT',, 
        2                    MSGBUF.ONAME, 
        2                    ONAME_LEN) 
        IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS)) 
        ! Remove unit number from ONAME and set up counted string 
        ONAME_LEN = ONAME_LEN - 3 
        MSGBUF.ONAME(2:ONAME_LEN+1) = MSGBUF.ONAME(1:ONAME_LEN) 
        MSGBUF.ONAME(1:1) = CHAR(ONAME_LEN) 
        ! Call $SNDOPR 
        STATUS = SYS$SNDOPR (MSGBUF.STRING,) 
        IF (.NOT. STATUS) CALL LIB$SIGNAL(%VAL(STATUS)) 
        END

This Compaq Fortran for OpenVMS program enables the current terminal to receive OPER1 operator messages.

$SPACE

The Space service lets you space (skip) a tape file forward or backward a specified number of blocks.
Refer to the OpenVMS Record Management Services Reference Manual for additional information about this service.

$START_ALIGN_FAULT_REPORT (Alpha Only)

On Alpha systems, initializes user image alignment fault reporting.

Format

SYS$START_ALIGN_FAULT_REPORT report_method ,report_buffer ,buffer_length

C Prototype

int sys$start_align_fault_report (int report_method, void *report_buffer, int buffer_length);

Arguments

report_method

OpenVMS usage: longword_signed

type: longword (signed)

access: read

mechanism: by value

Method by which image alignment faults are to be reported.
The following table shows valid values for the report_method argument:

Value Meaning

AFR$C_BUFFERED Alignment fault PCs and fault addresses are saved in a user-supplied buffer.

AFR$C_EXCEPTION Alignment faults are elevated to user mode exceptions.

report_buffer

OpenVMS usage: address

type: longword (unsigned)

access: read

mechanism: by reference

The 32-bit address of the buffer into which to write the fault data. The report_buffer argument is needed only if the value of the report_method argument is AFR$C_BUFFERED.
buffer_length

OpenVMS usage: byte count

type: longword (signed)

access: read

mechanism: by value

Length of the buffer specified in the report_buffer argument.
The buffer must have a minimum size of AFR$K_USER_LENGTH + 32. However, a larger buffer allows for more information to be collected.

Value	Meaning
AFR$C_BUFFERED	Alignment fault PCs and fault addresses are saved in a user-supplied buffer.
AFR$C_EXCEPTION	Alignment faults are elevated to user mode exceptions.

Description

The Start Alignment Fault Reporting service initializes user image alignment fault reporting.
The $START_ALIGN_FAULT_REPORT service allows the user to gather alignment fault data for one image. Reporting is enabled for the life of the image. When the image terminates, the alignment fault reporting is disabled.
User alignment fault data can be written to a buffer or broadcast as an informational exception message.
If the AFR$C_BUFFERED value is given in the report_method buffer, alignment fault PCs and fault addresses are saved in a user-supplied buffer.
The following diagram illustrates the format in which user alignment fault data is stored in the buffer:

If the AFR$C_EXCEPTION value is given in the report_method argument, alignment faults are elevated to user mode exceptions. These exceptions can be trapped in a handler; otherwise, an informational exception message might be broadcast and the program continues to execute.

Required Access or Privileges

None

Required Quota

None

Related Services

$GET_ALIGN_FAULT_DATA, $GET_SYS_ALIGN_FAULT_DATA, $INIT_SYS_ALIGN_FAULT_REPORT, $PERM_DIS_ALIGN_FAULT_REPORT, $PERM_REPORT_ALIGN_FAULT, $STOP_ALIGN_FAULT_REPORT, $STOP_SYS_ALIGN_FAULT_REPORT

Condition Values Returned

SS$_NORMAL The service completed successfully.

SS$_ACCVIO The buffer specified in the report_buffer argument is not accessible.

SS$_AFR_ENABLED The service has already been called for this image.

SS$_ARG_GTR_32_BITS The report buffer's virtual address lies in 64-bit virtual address space.

SS$_ALIGN The buffer specified in the report_buffer argument is not quadword aligned.

SS$_BADPARAM The buffer size is smaller than that defined by the AFR$K_USER_LENGTH + 32 symbol.

Example


#include <afrdef> #include <stdio> #include <ssdef> #define USER_BUFFER_ITEMS 10 #define GET_BUFFER_SIZE USER_BUFFER_ITEMSAFR$K_USER_LENGTH #define SAVE_BUFFER_SIZE 128+64 #define fault_pc afr$l_fault_pc_l #define fault_va afr$l_fault_va_l static int usr_buff_len; static char usr_buff; static int rep_method; void cause_af() { int addr; int ptr; int arr[2]; addr = (int) &arr[0]; ptr = (int ) ++addr; ptr = 1; / cause alignment fault / } main() { int i; char get_buffer[GET_BUFFER_SIZE]; struct afrdef data_item; int offset; int status; int return_size; rep_method = AFR$C_BUFFERED; usr_buff_len = SAVE_BUFFER_SIZE; usr_buff = (char )malloc (usr_buff_len); if(( status = sys$start_align_fault_report(rep_method, usr_buff, usr_buff_len)) != SS$_NORMAL) return(status); for (i=0;i<USER_BUFFER_ITEMS;i++) cause_af(); while (((status = sys$get_align_fault_data (get_buffer, GET_BUFFER_SIZE, &return_size)) > 0) && (return_size > 0)) { / got some data, print it / offset = 0; while (offset < return_size) { data_item = (struct afrdef )(&get_buffer[offset]); printf ("Alignment fault at PC = %8.8X, VA = %8.8X\n", data_item->fault_pc, data_item->fault_va); offset += AFR$K_USER_LENGTH; } } return (status); }

#include <afrdef>  
#include <stdio> 
#include <ssdef> 
 
#define USER_BUFFER_ITEMS  10 
#define GET_BUFFER_SIZE    USER_BUFFER_ITEMS*AFR$K_USER_LENGTH 
#define SAVE_BUFFER_SIZE   128+64 
 
#define fault_pc afr$l_fault_pc_l 
#define fault_va afr$l_fault_va_l 
 
static int usr_buff_len; 
static char *usr_buff; 
static int rep_method; 
 
 
void 
cause_af() 
{ 
  int     addr; 
  int     *ptr; 
  int    arr[2]; 
 
  addr = (int) &arr[0]; 
  ptr = (int *) ++addr; 
  *ptr = 1;    /* cause alignment fault */ 
} 
 
 
main() 
{ 
  int            i; 
  char           get_buffer[GET_BUFFER_SIZE]; 
  struct afrdef  *data_item; 
  int            offset; 
  int            status; 
  int            return_size; 
 
  rep_method = AFR$C_BUFFERED; 
  usr_buff_len = SAVE_BUFFER_SIZE; 
  usr_buff = (char *)malloc (usr_buff_len); 
  if(( status = sys$start_align_fault_report(rep_method, usr_buff, 
               usr_buff_len)) 
      != SS$_NORMAL) return(status); 
 
  for (i=0;i<USER_BUFFER_ITEMS;i++) 
    cause_af(); 
 
  while (((status = sys$get_align_fault_data (get_buffer, 
                GET_BUFFER_SIZE, 
                &return_size)) > 0) && 
         (return_size > 0)) { 
    /* got some data, print it */ 
    offset = 0; 
    while (offset < return_size) { 
      data_item = (struct afrdef *)(&get_buffer[offset]); 
      printf ("Alignment fault at PC = %8.8X, VA = %8.8X\n", 
        data_item->fault_pc, data_item->fault_va); 
      offset += AFR$K_USER_LENGTH; 
    } 
  } 
 
  return (status); 
}

This example shows how to use the $START_ALIGN_FAULT_REPORT service to initialize user image alignment fault reporting on Alpha systems.

$START_BRANCH

Adds a new branch to a transaction.

Format

SYS$START_BRANCH [efn] ,[flags] ,iosb ,[astadr] ,[astprm] ,tid ,tm_name ,bid [,[timout], [acmode], [tx_class]]

C Prototype

int sys$start_branch (unsigned int efn, unsigned int flags, struct _iosb *iosb, void (*astadr)(__unknown_params), int astprm, unsigned int tid [4], void *tm_name, unsigned int bid [4],...);

Arguments

efn

OpenVMS usage: ef_number

type: longword (unsigned)

access: read only

mechanism: by value

Number of the event flag that is set when the service completes. If this argument is omitted, event flag 0 is used.
flags

OpenVMS usage: mask_longword

type: longword (unsigned)

access: read only

mechanism: by value

Flags specifying options for the service. The flags argument is a longword bit mask in which each bit corresponds to an option flag. The $DDTMDEF macro defines symbolic names for these option flags, described in Table SYS-56. All undefined bits must be 0. If this argument is omitted, no flags are used.

Table SYS-56 $START_BRANCH Option Flags
Flag Name Description

DDTM$M_BRANCH_UNSYNCHED Specifies that the new branch is unsynchronized.
If this flag is clear, the new branch is synchronized.

DDTM$M_NONDEFAULT Set this flag if you do not want the transaction to be the default transaction of the calling process. If this flag is clear, the transaction becomes the default transaction of the calling process.
An error is returned if this flag is clear and the calling process has an current default transaction.

DDTM$M_SYNC Specifies successful synchronous completion by returning SS$_SYNCH. When SS$_SYNCH is returned, the AST routine is not called, the event flag is not set, and the I/O status block is not filled in.

iosb

OpenVMS usage: io_status_block

type: quadword (unsigned)

access: write only

mechanism: by reference

The I/O status block in which the completion status of the service is returned as a condition value. See the Condition Values Returned section.
The following diagram shows the structure of the I/O status block:

**Table SYS-56 $START_BRANCH Option Flags**
Flag Name	Description
DDTM$M_BRANCH_UNSYNCHED	Specifies that the new branch is unsynchronized. If this flag is clear, the new branch is synchronized.
DDTM$M_NONDEFAULT	Set this flag if you do not want the transaction to be the default transaction of the calling process. If this flag is clear, the transaction becomes the default transaction of the calling process. An error is returned if this flag is clear and the calling process has an current default transaction.
DDTM$M_SYNC	Specifies successful synchronous completion by returning SS$_SYNCH. When SS$_SYNCH is returned, the AST routine is not called, the event flag is not set, and the I/O status block is not filled in.

astadr

OpenVMS usage:	ast_procedure
type:	procedure entry mask
access:	call without stack unwinding
mechanism:	by reference

The AST routine executed when the service completes, if SS$_NORMAL is returned in R0. The astadr argument is the address of the entry mask of this routine. The routine is executed in the same access mode as that of the caller of the $START_BRANCH service.

astprm

OpenVMS usage:	user_arg
type:	longword (unsigned)
access:	read only
mechanism:	by value

The AST parameter passed to the AST routine specified by the astadr argument.

tid

OpenVMS usage:	trans_id
type:	octaword (unsigned)
access:	read only
mechanism:	by reference

The identifier (TID) of the transaction to which the new branch will be added.

tm_name

OpenVMS usage:	char_string
type:	character-coded text string
access:	read only
mechanism:	by descriptor--fixed-length string descriptor

The name of the node on which the call was made to $ADD_BRANCH that authorized the new branch to be added to the transaction. Note that this cannot be a cluster alias.

To ensure smooth operation in a mixed-network environment, refer to the chapter entitled Managing DECdtm Services in the OpenVMS System Manager's Manual, for information on defining node names.

bid

OpenVMS usage:	branch_id
type:	octaword (unsigned)
access:	read only
mechanism:	by reference

The identifier (BID) of the new branch that is to be added to the transaction.

An BID value of zero is invalid.

timout

OpenVMS usage:	date_time
type:	quadword (unsigned)
access:	read only
mechanism:	by reference

Reserved to Compaq.

acmode

OpenVMS usage:	access_mode
type:	longword (unsigned)
access:	read only
mechanism:	by value

The access mode of the new branch in this process. This is the least privileged mode that a caller must be in to remove this branch from the transaction by calling $END_BRANCH. Note that it can be removed from the transaction by calling $ABORT_TRANS from any access mode.

This argument only influences the access mode of the first branch in this process. Subsequent branches have the same access mode as the first. The access mode of the new branch is the least privileged of:

The access mode of the caller.
The access mode specified by the acmode argument.

Note that if a branch already exists in this process, then neither the access mode of the caller nor the access mode specified by the acmode argument may be less privileged than that branch.

The default value of this argument is the access mode of the caller.

tx_class

OpenVMS usage:	char_string
type:	character-coded text string
access:	read only
mechanism:	by descriptor--fixed-length string descriptor

A string that specifies the transaction class for the transaction on the local node if the transaction does not already have a transaction class on the local node. This string is passed in the event reports delivered to Resource Manager identifiers (RMIs) and Resource Manager (RM) participants on the local node.

This argument is ignored if the transaction already has a transaction class on the local node.

This string must be no longer than 31 characters.

Description

The $START_BRANCH system service:

Adds a new branch running in the calling process to the specified transaction.
Adds the local DECdtm transaction manager to the specified transaction if the local DECdtm transaction manager is not already a participant in that transaction.
Sets the default transaction of the calling process to the new transaction, if the DDTM$M_NONDEFAULT flag is clear and the process does not have a default transaction.
Delivers a transaction started event to each RMI in the calling process that meets both of the following conditions:

Requested Transaction Started events for the corresponding transaction type (default or non-default)
Has an access mode that is the same as or more privileged than that specified in this call to $START_BRANCH.

The new branch should have been previously authorized. Authorization is provided either by a matching call to $JOIN_RM with the DDTM$M_COORDINATOR flag set or by a matching call to $ADD_BRANCH. Two calls, one to $ADD_BRANCH and one to $START_BRANCH or one to $JOIN_RM and one to $START_BRANCH, are said to be matching when the following conditions are true:

The same TID values are passed to both calls.
The BID returned by the call to $ADD_BRANCH or $JOIN_RM is the same as that passed to the call to $START_BRANCH.
The call to $START_BRANCH is made on the node identified by the tm_name argument passed to the call to $ADD_BRANCH or on the node on which the call to $JOIN_RM was made.
The call to $ADD_BRANCH or $JOIN_RM is made on the node identified by the tm_name argument passed to the call to $START_BRANCH.

$START_BRANCH does not check that there has been a matching call to $ADD_BRANCH or $JOIN_RM unless the tm_name argument passed to $START_BRANCH specifies the local node.

Note
The atomicity of the transaction is not guaranteed if there is a call to $START_BRANCH that does not have a matching call to $ADD_BRANCH or $JOIN_RM.

Preconditions for the successful completion of $START_BRANCH are:

The local node must have a DECdtm transaction log.
The TP_SERVER process must be running on the local node.
There must not have been a successful call to $START_BRANCH on the local node that passed the specified BID.
If the tm_name argument specifies the local node, there must have been a matching call to $ADD_BRANCH or $JOIN_RM on the local node.
If the DDTM$M_NONDEFAULT flag is clear, the calling process must not have an unended default transaction.
If this process already contains a branch of this transaction, then the access mode of the caller must be the same as or more privileged than the access mode of that branch.

$START_BRANCH may fail because:

Preconditions were not met.
An abort event occurred for the transaction.
A call to $END_TRANS to end the transaction is in progress and it is too late to add a new branch to the transaction.
The DDTM$M_NONDEFAULT flag was clear and a call to $SET_DEFAULT_TRANS by the calling process is in progress.

When $START_BRANCH completes successfully:

A new branch running in the calling process has been added to the transaction.
All Transaction Started events reported to RMIs in the calling process have been acknowledged.
If the DDTM$M_NONDEFAULT flag was clear, the transaction is the default transaction of the calling process.

A branch may:

Invoke resource manager operations, explicitly passing the TID.
Invoke resource manager operations without specifying the TID, if the transaction is the default transaction of the calling process, and the resource manager supports default transactions.
Call $ADD_BRANCH to authorize another branch to be added to the transaction.

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privacy and legal statement

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SS$_NORMAL	The service completed successfully.
SS$_ACCVIO	The message buffer or buffer descriptor cannot be read by the caller.
SS$_BADPARAM	The specified message has a length of 0 or has more than 986 bytes.
SS$_DEVNOTMBX	The channel specified is not assigned to a mailbox.
SS$_INSFMEM	The service was called from kernel mode or the system dynamic memory is insufficient for completing the service.
SS$_IVCHAN	You specified an invalid channel number. An invalid channel number is one that is 0 or a number larger than the number of channels available.
SS$_MBFULL	The mailbox used to support communication is full. Retry at a later time.
OPC$_NOPERATOR	The service completed successfully; the Operator Communications Manager (OPCOM) is not running and the message will not be sent. Note that OPC$_NOPERATOR is a success status and must be tested for explicitly.
SS$_NOPRIV	The process does not have the privilege to reply to or cancel a user's request; the process does not have read/write access to the specified mailbox; or the channel was assigned from a more privileged access mode.

OPC$_BLANKTAPE	The service completed successfully; the operator responded with the DCL command REPLY/BLANK_TAPE=n.
OPC$_INITAPE	The service completed successfully; the operator responded with the DCL command REPLY/INITIALIZE_TAPE=n.
OPC$_NOPERATOR	The service completed successfully; no operator terminal was enabled to receive the message.
OPC$_RQSTCMPLTE	The service completed successfully; the operator completed the request.
OPC$_RQSTPEND	The service completed successfully; the operator will perform the request when possible.
OPC$_RQSTABORT	The operator could not satisfy the request.
OPC$_RQSTCAN	The caller canceled the request.

OpenVMS usage:	longword_signed
type:	longword (signed)
access:	read
mechanism:	by value

OpenVMS usage:	address
type:	longword (unsigned)
access:	read
mechanism:	by reference

OpenVMS usage:	byte count
type:	longword (signed)
access:	read
mechanism:	by value

OpenVMS usage:	ef_number
type:	longword (unsigned)
access:	read only
mechanism:	by value

OpenVMS usage:	mask_longword
type:	longword (unsigned)
access:	read only
mechanism:	by value

OpenVMS usage:	io_status_block
type:	quadword (unsigned)
access:	write only
mechanism:	by reference