Re: How/When does the kernel know to load a module?

Kirk Petersen (
Sat, 24 Apr 1999 14:01:36 -0700

> My first question is by what means the bare kernel knows that it needs a
> function residing in a module?

It is up to each part of the kernel to determine when a module is
required and load it. It isn't something that happens by function
dependencies, like linking a binary might. A good example is
sock_create() in linux/net/socket.c. When a socket is created, a call
to request_module() is made with 'net-pf-%d' where the %d is filled in
by the socket family. request_module() is what execve()s modprobe and
does the actual work.

> For example: I traced the souce code of the network. As the bare kernel
> setting up, it calls 'net_dev_init()'. 'net_dev_init()' will follow the
> link: 'dev_base' to autoprobe net devices. I have a NE2000 card. I think
> the kernel would call 'ne_probe()',( the function is in the module ne.o
> ), but it didn't. The ne.o module is loaded only when the 'rc.d' shell
> runs 'ifconfig eth0...'. My second question is why the kernel didn't
> call 'ne_probe()' at first? and is it the 'ifconfig' informs the kernel
> to load a module? and by what means to inform?

ifconfig tells the kernel to configure eth0, for example, and the
kernel eventually calls request_module() with 'eth0'. The user has,
hopefully, aliased eth0 to something like 'ne' and modprobe therefore
loads the ne.o module (and any other module that ne.o depends on).
When ne.o is loaded, its init_module() function is called, which
registers some callback functions that get called to do things like
send/receive packets or probe the card.

Kirk Petersen

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