February 1998
Intermediate to advanced
439 pages
13h 46m
English
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Opening and Closing
Our driver can probe for the interface at module load time or at kernel boot. The next step is to assign an address to the interface so the driver can exchange data through it. Opening and closing an interface is performed by the ifconfig command.
When ifconfig is used to assign an address to the interface,
it performs two tasks. First, it assigns the address
by means of ioctl(SIOCSIFADDR) (Socket I/O
Control Set InterFace ADDRess). Then it sets the IFF_UP bit in
dev->flag by means of ioctl(SIOCSIFFLAGS) (Socket
I/O Control Set InterFace FLAGS) to turn the interface on.
As far as the device is concerned, ioctl(SIOCSIFADDR) sets
dev->pa_addr, dev->family, dev->pa_mask, and
dev->pa_brdaddr, but no driver function is invoked--the task
is device-independent, and the kernel performs it. The latter
command (ioctl(SIOCSIFFLAGS)), though, calls the
open method for the device.
Similarly, when the interface is shut down, ifconfig uses
ioctl(SIOCSIFFLAGS) to clear IFF_UP, and the stop
method is called.
Both device methods return 0 in case of success and the usual negative value in case of error.
As far as the actual code is concerned, the driver has to perform the same tasks as the char and block drivers do. open requests any system resources it needs and tells the interface to come up; stop shuts down the interface and releases system resources.
One last step is needed if the driver isn’t going to use shared interrupts (for example, if it is to be compatible with older ...
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