The following section contains miscellaneous technical information about EtherShare. It is primarily of interest to experienced system administrators only.
In order to be able to communicate using the AppleTalk protocols, EtherShare needs support from the operating system. Commonly, UNIX suppliers deliver the TCP/IP networking protocols together with their standard operating system release, but no AppleTalk networking protocols. EtherShare thus contains drivers that implement the AppleTalk protocol with Ethernet. On some machines, EtherShare also supports other network connections. All files that relate to the kernel side of the EtherShare system reside in the directory “HELIOSDIR/etc/kernel”. The following is a detailed description of what is changed in the operating system by the EtherShare installation. This is probably of interest to advanced UNIX users only, since the EtherShare configuration shell scripts hide most of the details necessary to get the AppleTalk drivers running.
The kernel modules come in two flavors depending on host operating system architecture. System V.4 based systems use a stream-based architecture where each AppleTalk communication endpoint is represented as a file descriptor opened through the streams multiplexor “/dev/ddp”. Berkeley-based systems use file descriptors opened through the socket mechanism.
Solaris and IBM RS/6000 systems support a concept of loading drivers, which can be loaded into the operating system during runtime. In such cases, it is not necessary to re-link the UNIX kernel with new modules. The “start-helios” shell script takes care of loading the driver when starting AppleTalk, if the driver is not already loaded.
EtherShare uses two kernel modules on Solaris systems, “aarp” contains the “AppleTalk Address Resolution Protocol” streams module and “ddp” the “Datagram Delivery Protocol” streams multiplexor. “aarp” is located in “/kernel/strmod” and “ddp” in “/kernel/drv”. During installation the files are copied from “HELIOSDIR/etc/kernel” to the “/kernel” directory. In addition, the installation script adds a line to the “/etc/minor_perm” and “/etc/devlink.tab” and files to get the proper link from “/devices/ pseudo /clone:ddp” entry to “/dev/ddp” using the proper permissions. The drivers are loaded and unloaded by Solaris automatically, no loading or unloading should be necessary.
A long list of all loaded modules can be produced by using the “modinfo” command. The “modunload” command can be used to unload the drivers, but only if they are unused.
On IBM RS/6000 systems, only one driver is loaded by the “start-helios” script (“HELIOSDIR/etc/kernel/atalk”). This driver is dependent upon the AIX version. The installation procedure makes a link from the corresponding and appropriate file to “/usr/lib/drivers”.
In addition, entries are added to the ODM database, to allow the loading of the driver through the “mkdev” command. The logical name for the kernel module is “atalk0”. Use the following command to load the module:
# mkdev -t atalk
The “lsdev” command can be used to see if the kernel module is loaded:
# lsdev -C -l atalk0
On AIX, the unloading of network protocols is not supported.