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Technical Reference: Communications, Volume 1
read Subroutine Extended Parameters for DLC
Purpose
Provide generic data link control (GDLC) with a structure
to return data types and service access point (SAP) and link station (LS)
correlators.
Syntax
#define DLC_INFO 0x80000000
#define DLC_XIDD 0x40000000
#define DLC_DGRM 0x20000000
#define DLC_NETD 0x10000000
#define DLC_OFLO 0x00000002
#define DLC_RSPP 0x00000001
struct dlc_io_ext
{
__ulong32_t sap_corr;
__ulong32_t ls_corr;
__ulong32_t flags;
__ulong32_t dlh_len;
};
Description
An extended read or readx subroutine must be issued by an application user to provide GDLC
with a structure to return the type of data and the SAP and LS correlators.
Parameters
sap_corr |
Specifies the user's SAP identifier of the received data. |
ls_corr |
Specifies the user's LS identifier of the received data. |
flags |
Specifies flags for the readx subroutine. The
following flags are supported:
- DLC_INFO
- Indicates that normal sequenced data has been received for a link
station using an I-Frame Data Received routine.
If buffer overflow (OFLO) is indicated, the received data has been truncated
because the received data length exceeds either the maximum I-field size derived
at completion of DLC_START_LS
ioctl operation or the application user's buffer size.
- DLC_XIDD
- Indicates that exchange identification (XID) data has been received
for a link station using an XID Data Received
routine. If buffer overflow (OFLO) is indicated, the received XID has been
truncated because the received data length exceeds either the maximum I-field
size derived at DLC_START_LS completion or the application
user's buffer size. If response pending (RSPP) is indicated, an XID response
is required and must be provided to GDLC using a write XID as soon as possible
to avoid repolling and possible termination of the remote LS.
- DLC_DGRM
- Indicates that a datagram has been received for an LS using a Datagram Data Received routine. If buffer overflow (OFLO) is indicated,
the received data has been truncated because the received data length exceeds
either the maximum I-field size derived at DLC_START_LS
completion or the application user's buffer size.
- DLC_NETD
- Indicates that data has been received from the network for a service
access point using a Network Data Received routine.
This may be link-establishment data such as X.21 call-progress signals or
Smartmodem command responses. It can also be data destined for the user's
SAP when no link station has been started that fits the addressing of the
packet received. If buffer overflow (OFLO) is indicated, the received data
has been truncated because the received data length exceeds either the maximum
packet size derived at DLC_ENABLE_SAP completion or the application user's buffer size.
Network data
contains the entire MAC layer packet, excluding any fields stripped by the
adapter such as Preamble or CRC.
- DLC_OFLO
- Indicates that overflow of the user data area has occurred and the
data was truncated. This error does not set a u.u_error
indication.
- DLC_RSPP
- Indicates that the XID received requires an XID response to be sent
back to the remote link station.
|
dlh_len |
Specifies data link header length. This field has a different meaning
depending on whether the extension is for a readx subroutine
call to GDLC or a response from GDLC.
On the application readx subroutine,
this field indicates whether the user wishes to have datalink header information
prefixed to the data. If this field is set to 0 (zero), the data link header
is not to be copied (only the I-field is copied).
If this field is set to any nonzero value, the data link header information
is included in the read operation.
On the response to an application readx subroutine, this field contains the number of data
link header bytes received and copied into the data link header information
field.
On asynchronous receive function handlers to the kernel user,
this field contains the length of the data link header within the communications
memory buffer (mbuf). |
These DLC extended parameters for the read subroutine are part of the data link control in BOS Extensions 2
for the device manager you are using.
Related Information
The read, readx, readv, or readvx subroutine.
List of Kernel Routines for
DLC.
Parameter Blocks by ioctl
Operation for DLC.
write Subroutine Extended Parameters
for DLC.
Generic Data Link Control
(GDLC) Environment Overview in AIX 5L Version 5.2 Communications Programming Concepts.
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