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NCB info  Overview  Group

The NCB structure represents a network control block. It contains information about the command to perform, an optional post routine, an optional event handle, and a pointer to a buffer that is used for messages or other data. A pointer to this structure is passed to the Netbios function.

typedef struct _NCB { // ncb 

    UCHAR  ncb_command; 

    UCHAR  ncb_retcode; 

    UCHAR  ncb_lsn; 

    UCHAR  ncb_num; 

    PUCHAR ncb_buffer; 

    WORD   ncb_length; 

    UCHAR  ncb_callname[NCBNAMSZ]; 

    UCHAR  ncb_name[NCBNAMSZ]; 

    UCHAR  ncb_rto; 

    UCHAR  ncb_sto; 

    void (*ncb_post) (struct _NCB *); 

    UCHAR  ncb_lana_num; 

    UCHAR  ncb_cmd_cplt; 

    UCHAR  ncb_reserve[10]; 

    HANDLE ncb_event; 

} NCB; 

 

Members

ncb_command
Specifies the command code and a flag that indicates whether the NCB structure is processed asynchronously. The most significant bit contains the flag. If the ASYNCH constant is combined with a command code (by using the OR operator), the NCB structure is processed asynchronously. The following command codes are supported.

Code

Meaning

NCBACTION

Windows NT only: Enables extensions to the transport interface. NCBACTION is mapped to TdiAction. When this code is specified, the ncb_buffer member points to a buffer to be filled with an ACTION_HEADER structure, which is optionally followed by data. NCBACTION commands cannot be canceled by using NCBCANCEL.

NCBACTION is not a standard NetBIOS 3.0 command.

NCBADDGRNAME

Adds a group name to the local name table. This name cannot be used by another process on the network as a unique name, but it can be added by anyone as a group name.

NCBADDNAME

Adds a unique name to the local name table. The TDI driver ensures that the name is unique across the network.

NCBASTAT

Retrieves the status of either a local or remote adapter. When this code is specified, the ncb_buffer member points to a buffer to be filled with an ADAPTER_STATUS structure, followed by an array of NAME_BUFFER structures.

NCBCALL

Opens a session with another name.

NCBCANCEL

Cancels a previous pending command.

NCBCHAINSEND

Sends the contents of two data buffers to the specified session partner.

NCBCHAINSENDNA

Sends the contents of two data buffers to the specified session partner and does not wait for acknowledgment.

NCBDELNAME

Deletes a name from the local name table.

NCBDGRECV

Receives a datagram from any name.

NCBDGRECVBC

Receives a broadcast datagram from any name.

NCBDGSEND

Sends datagram to a specified name.

NCBDGSENDBC

Sends a broadcast datagram to every host on the local area network (LAN).

NCBENUM

Windows NT only: Enumerates LAN adapter (LANA) numbers. When this code is specified, the ncb_buffer member points to a buffer to be filled with a LANA_ENUM structure.

NCBENUM is not a standard NetBIOS 3.0 command.

NCBFINDNAME

Determines the location of a name on the network. When this code is specified, the ncb_buffer member points to a buffer to be filled with a FIND_NAME_HEADER structure followed by one or more FIND_NAME_BUFFER structures.

NCBHANGUP

Closes a specified session.

NCBLANSTALERT

Windows NT only: Notifies the user of LAN failures that last for more than one minute.

NCBLISTEN

Enables a session to be opened with another name (local or remote).

NCBRECV

Receives data from the specified session partner.

NCBRECVANY

Receives data from any session corresponding to a specified name.

NCBRESET

Resets a LAN adapter. An adapter must be reset before it can accept any other NCB command that specifies the same number in the ncb_lana_num member.

Use the following values to specify how resources are to be freed:

  • If ncb_lsn is not 0x00, all resources associated with ncb_lana_num are to be freed.
  • If ncb_lsn is 0x00, all resources associated with ncb_lana_num are to be freed, and new resources are to be allocated. The ncb_callname[0] byte specifies the maximum number of sessions, and the ncb_callname[2] byte specifies the maximum number of names. A nonzero value for the ncb_callname[3] byte requests that the application use NAME_NUMBER_1.

NCBSEND

Sends data to the specified session partner.

NCBSENDNA

Sends data to specified session partner and does not wait for acknowledgment.

NCBSSTAT

Retrieves the status of the session. When this value is specified, the ncb_buffer member points to a buffer to be filled with a SESSION_HEADER structure, followed by one or more SESSION_BUFFER structures.

NCBTRACE

Activates or deactivates NCB tracing.

This command is not supported.

NCBUNLINK

Unlinks the adapter.

This command is provided for compatibility with earlier versions of NetBIOS. It has no effect in Windows NT or Windows 95.

ncb_retcode
Specifies the return code. This value is set to NRC_PENDING while an asynchronous operation is in progress. The system returns one of the following values:

Value

Meaning

NRC_GOODRET

The operation succeeded.

NRC_BUFLEN

An illegal buffer length was supplied.

NRC_ILLCMD

An illegal command was supplied.

NRC_CMDTMO

The command was timed out.

NRC_INCOMP

The message was incomplete. The application is to issue another command.

NRC_BADDR

The buffer address was illegal.

NRC_SNUMOUT

The session number was out of range.

NRC_NORES

No resource was available.

NRC_SCLOSED

The session was closed.

NRC_CMDCAN

The command was canceled.

NRC_DUPNAME

A duplicate name existed in the local name table.

NRC_NAMTFUL

The name table was full.

NRC_ACTSES

The command finished; the name has active sessions and is no longer registered.

NRC_LOCTFUL

The local session table was full.

NRC_REMTFUL

The remote session table was full. The request to open a session was rejected.

NRC_ILLNN

An illegal name number was specified.

NRC_NOCALL

The system did not find the name that was called.

NRC_NOWILD

Wildcards are not permitted in the ncb_name member.

NRC_INUSE

The name was already in use on the remote adapter.

NRC_NAMERR

The name was deleted.

NRC_SABORT

The session ended abnormally.

NRC_NAMCONF

A name conflict was detected.

NRC_IFBUSY

The interface was busy.

NRC_TOOMANY

Too many commands were outstanding; the application can retry the command later.

NRC_BRIDGE

The ncb_lana_num member did not specify a valid network number.

NRC_CANOCCR

The command finished while a cancel operation was occurring.

NRC_CANCEL

The NCBCANCEL command was not valid; the command was not canceled.

NRC_DUPENV

The name was defined by another local process.

NRC_ENVNOTDEF

The environment was not defined. A reset command must be issued.

NRC_OSRESNOTAV

Operating system resources were exhausted. The application can retry the command later.

NRC_MAXAPPS

The maximum number of applications was exceeded.

NRC_NOSAPS

No service access points (SAPs) were available for NetBIOS.

NRC_NORESOURCES

The requested resources were not available.

NRC_INVADDRESS

The NCB address was not valid.

This return code is not part of the IBM NetBIOS 3.0 specification and is not returned in the NCB structure. Instead, it is returned by Netbios.

NRC_INVDDID

The NCB DDID was invalid.

NRC_LOCKFAIL

The attempt to lock the user area failed.

NRC_OPENERR

An error occurred during an open operation being performed by the device driver. This error code is not part of the NetBIOS 3.0 specification.

NRC_SYSTEM

A system error occurred.

NRC_PENDING

An asynchronous operation is not yet finished.

ncb_lsn
Identifies the local session number. This number uniquely identifies a session within an environment. This number is returned by Netbios after a successful NCBCALL command.
ncb_num
Specifies the number for the local network name. This number is returned by Netbios after a successful NCBADDNAME or NCBADDGRNAME command. This number, not the name, must be used with all datagram commands and for NCBRECVANY commands.

The number for NAME_NUMBER_1 is always 0x01. Netbios assigns values in the range 0x02 to 0xFE for the remaining names.

ncb_buffer
Points to the message buffer. The buffer must have write access. Its uses are as follows:

Command

Purpose

NCBSEND

Contains the message to be sent.

NCBRECV

Receives the message.

NCBSSTAT

Receives the requested status information.

ncb_length
Specifies the size, in bytes, of the message buffer. For receive commands, this member is set by the Netbios function to indicate the number of bytes received.

If the buffer length is incorrect, the Netbios function returns the NRC_BUFLEN error code.

ncb_callname
Specifies the name of the remote application. Trailing-space characters should be supplied to make the length of the string equal to NCBNAMSZ.
ncb_name
Specifies the name by which the application is known. Trailing-space characters should be supplied to make the length of the string equal to NCBNAMSZ.
ncb_rto
Specifies the time-out period for receive operations, in 500-millisecond units, for the session. A value of zero implies no time-out. Specify with the NCBCALL or NCBLISTEN command. Affects subsequent NCBRECV commands.
ncb_sto
Specifies the time-out period for send operations, in 500-millisecond units, for the session. A value of zero implies no time-out. Specify with the NCBCALL or NCBLISTEN command. Affects subsequent NCBSEND and NCBCHAINSEND commands.
ncb_post
Specifies the address of the post routine to call when the asynchronous command is completed. The post routine is defined as:

NCB_POST PostRoutine( PNCB pncb );

where the pncb parameter is a pointer to the completed network control block.

ncb_lana_num
Specifies the LAN adapter number. This zero-based number corresponds to a particular transport provider using a particular LAN adapter board.
ncb_cmd_cplt
Specifies the command complete flag. This value is the same as the ncb_retcode member.
ncb_reserve
Reserved; must be zero.
ncb_event
Specifies a handle to a Windows event that is set to the nonsignaled state when an asynchronous command is accepted, and it is set to the signaled state when the asynchronous command is completed. The event is signaled if the Netbios function returns a nonzero value. Only manual reset events should be used for synchronization. A specified event should not be associated with more than one active asynchronous command.

The ncb_event member must be zero if the ncb_command member does not have the ASYNCH flag set or if ncb_post is nonzero. Otherwise, Netbios returns the NRC_ILLCMD error code.

Remarks

Using ncb_event to issue asynchronous requests requires fewer system resources than using ncb_post. In addition, when ncb_event is nonzero, the pending request is canceled if the thread terminates before the request is processed. This is not true for asynchronous requests sent using ncb_post.

See Also

ACTION_HEADER, ADAPTER_STATUS, FIND_NAME_BUFFER, FIND_NAME_HEADER, LANA_ENUM, NAME_BUFFER, Netbios, SESSION_BUFFER, SESSION_HEADER 

See also:


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