My ultimate goal is to be able to work with module source code on machines which are not connected to the Internet. Unfortunately, module-assistant requires an Internet connection. The question arises: is there a workaround?  Can I do the same thing without an Internet connection, and therefore without module-assistant?

In theory, module-assistant does only two things: install some packages; and place the appropriate symbolic link at /usr/src/linux.  The trick is to discover whether this is ALL that module-assistant does.  If so, we can get along without it, and install without access to the Internet.

So I did some before-and-after comparisons for two sequences.  The first sequence, with access to the Internet:

-- do a stock install of devuan from DVD
-- run dhclient
-- add deb http://deb.devuan.org/merged beowulf contrib main nonfree to /etc/apt/sources.list
-- in that same file, comment out the cdrom line
-- run apt-get update
-- run apt install module-assistant
-- run m-a prepare

Preparation for the second sequence:

-- download all packages installed in the previous ma-prepare

Now the second sequence, on a host without access to the Internet:

-- do a stock install of devuan from DVD
-- do NOT run dhclient
-- download from the mothership host a directory containing packages downloaded from the Internet
-- run dpkg --recursive --install that-directory
-- run

ln -s $(ls /usr/src | grep linux-headers | grep -v common) /usr/src/linux

Before-and-after comparisons were made by gathering the following data before, and then after, each sequence:

-- the names of all installed packages, found by running dpkg-query --list
-- the names of all files, basically a find / | sort
-- for each regular file less than 64k in length, the length and checksum

So, did the second sequence do as well as the first?  Yes, and actually a little better.  The only significant differences were that the second sequence created links in /etc/alternatives that the first did not (and, of course, package module-assistant itself wasn't installed).

It seems that module-assistant, when installing a package, did pretty much everything, but the output to the console looks different, as though module-assistant installed packages slightly different from how dpkg --install would. Indeed, that's so: links in /etc/alternatives are missing from the m-a prepare results.

Most importantly, m-a prepare didn't do anything other than what was advertised. So the second sequence is adequate, and solves the original "no Internet" problem.

Except:

One host of interest is older, a 32-bit machine.  I haven't tested this solution for 32 bits, but of course I will.  If I have any difficulty, I'll report it in this thread (unless the thread is closed at that point, or something).

# apt install module-assistant
# m-a prepare
# apt install dahdi{,-dkms}

Then reboot, ensure that the dahdi service is started and then use the various user space utilities to set things up.

apt install build-essential linux-headers-$(uname -r)

is what you normally need to compile anything other than a full kernel.

find / | sort

I assume that the names of the files containing the drivers would end with ".ko".

/usr/src/linux-patch-4.19-rt.patch.xz
/usr/src/linux-source-4.19.tar.xz

When I explode the source, I guess that's the, um, source. When I explode the patch file, it doesn't look like any diff output I've ever seen, and it doesn't look like a shell script of any sort. But I imagine I'm supposed to apply it to the source tree somehow. How do I do that?

EDIT: The drivers I'm compiling seem to be looking for a file named ".config" in the kernel source tree, but I don't see such a file in the expanded source tree. What would generate a ".config" file?