How to make one Linux kernel module depend on another external module with depmod?

Question

I'm writing a kernel module which depends on one existing kernel module. I'm building my module out of the tree (as an external module).

How can I declare the dependency, so that it is recognized by depmod?

Answer 1

While not entirely satisfying, the best I've come up with to make modprobe work is either adding an entry to modules.dep

# tail -1 modules.dep
../../../../home/ctuffli/mymod/mymod.ko: kernel/drivers/scsi/libsas/libsas.ko kernel/drivers/scsi/scsi_transport_sas.ko

or alternatively, symbolically linking the out-of-tree module to /lib/modules/ and let depmod figure out the dependencies

# ln -s /home/ctuffli/mymod/mymod.ko /lib/modules/2.6.31-19-server/kernel/drivers/scsi/
# depmod
# grep mymod /lib/modules/2.6.31-19-server/modules.dep
kernel/drivers/scsi/mymod.ko: kernel/drivers/scsi/libsas/libsas.ko kernel/drivers/scsi/scsi_transport_sas.ko

Answer 2

You don't need to. depmod will run through all modules in the current /lib/modules/ directory and build it's dependency tree based on unresolved symbols.

By default it will assume any symbol not provided by another module is in the kernel however you can use the -e/-F options to check that is the case too.