Reads receive data from generic data link control (GDLC).
#include <sys/device.h> #include <sys/gdlextcb.h>
int dlcread (devno, uiop, chan, ext) dev_t devno; struct uio *uiop; int chan, ext;
Note: The dlc prefix is replaced with the three-digit prefix for the specific GDLC device manager being read.
The dlcread entry point is called when a user application program invokes the readx subroutine. Kernel users do not call an fp_read kernel service. All receive data is returned to the user in the same order as received. The type of data that was read is indicated, as well as the service access point (SAP) and link station (LS) identifiers.
The following fields in the uio and iov structures are used to control the read-data transfer operation:
devno | Indicates major and minor device numbers. This is a dev_t device number that specifies both the major and minor device numbers of the GDLC device manager. One dev_t device number exists for each type of GDLC, such as Ethernet, Token-Ring, or SDLC. |
uiop | Points to the uio structure containing the read parameters. |
chan | Specifies the channel ID assigned by GDLC in the dlcmpx routine at open time. |
ext | Specifies the extended subroutine parameter. This is a pointer to the extended I/O structure. The argument to this parameter must always be in the application space. See the "read Subroutine Extended Parameters for DLC" for more information on this parameter. |
Successful read operations and those truncated due to limited user data space each return a value of 0 (zero). If more data is received from the media than will fit into the application data area, the DLC_OFLO value indicator is set in the command extension area (dlc_io_ext) to indicate that the read is truncated. All excess data is lost.
The following return values are defined in the /usr/include/sys/errno.h file:
Each GDLC supports the dlcread entry point as its switch table entry for the readx subroutine. The file system calls this entry point from the process environment only.
The open subroutine, readx subroutine.
The ddread device entry point.
The dlcmpx entry point of the GDLC device manager, dlcwrite entry point of the GDLC device manager.
The fp_lseek kernel service, fp_read kernel service, uiomove kernel service.
read Subroutine Extended Parameters for DLC.
Generic Data Link Control (GDLC) Environment Overview in AIX Version 4.3 Communications Programming Concepts.