read_conf(), called by nw_init(), reads the configuration file /etc/inet.conf and populates the arrays eth_conf[], psip_conf[], ip_conf[] and iftype[].
An example inet.conf file and the resulting arrays are shown in the following figure:
Note that "psip" stands for "pseudo ip", which is generally used over serial lines (as opposed to ethernet).
A fourth array, iftype[], correlates the interface type with the interface number (the index of the array). Since the same information in if_type[] can be found in ip_conf[], the code could have been rewritten using ip_conf[] where if_type[] was used. However, this would have limited the flexibility of the code since a network protocol other than ip could be added later.
iftype[] | 0th entry | 1st entry | 2nd entry | 3rd entry |
interface type | NETTYPE_ETH | NETTYPE_PSIP | 0 | 0 |
In addition to populating the four arrays, read_conf() also creates the necessary device files. For example, for the inet.conf file above, the following files (and their minor device numbers in parentheses) are created:
/dev/eth0 (1), /dev/ip0 (2), /dev/tcp0 (3), /dev/udp0 (4)
/dev/psip1 (17), /dev/ip1 (18), /dev/tcp1 (19), /dev/udp1 (20)
Note that the major device number for all of the network device files is set to the major device number of the /dev/ip file, which must be created before the network service can be started. The value of this major device number is 7 for the default configuration.
Links are also created for the default entry. For example, for the inet.conf file above, the following links are created:
/dev/eth -> /dev/eth0
/dev/ip -> /dev/ip0
/dev/tcp -> /dev/tcp0
/dev/udp -> /dev/udp0
From inet(8):
Inet starts as a normal process, reads the configuration file
/etc/inet.conf to see what it should do, and uses a few special low level
system calls to turn itself into a server. The format of the
configuration file is as follows:
Configuration
The inet configuration file is fairly simple, here is an example:
eth0 DP8390 0 { default; };
psip1;
It tells that network 0 (the one containing devices eth0, ip0, tcp0 and
udp0) uses the ethernet device driver handled by task "DP8390" at port 0.
This network is marked as the default network, so most programs use it
through the unnumbered devices like /dev/tcp or /dev/udp. Network 1 is a
Pseudo IP network that can be used for a serial IP over a modem for
instance.
ethN task port {options};
This sets up an ethernet with device name /dev/ethN, built on the
given ethernet device driver at the given port at that driver. (If
a network driver manages two network cards then they are at port 0
and 1.)
psipN {options};
Creates pseudo IP network /dev/psipN, usable for IP over serial
lines, tunnels and whatnot.
