playbook: debian{9,10}: Track distro kernel updates
Debian 9 and Debian10 ship linux-4.9.x and linux-4.19.x correspondingly. However kernel packages on those distributions include ABINAME as package version, for example linux-image-4.9.0-13-amd64 means linux 4.9.x with ABINAME=13.
The ABINAME is there because Linux sometimes breaks ABI compatibility in small places and Debian is very strict on not throwing ABI changes onto users unless requested. However even with that protection Debian "strongly recommends" to explicitly install just linux-image-amd64 - without ABINAME - which is just a dependency package that depends on the latest kernel in particular distribution series:
https://wiki.debian.org/DebianKernelABIChanges
The reason for this recommendation is that upstream Linux rarely breaks any ABI and even if there is a breakage it is so small and in obscure places that in practice it does not affect people.
Today, for Debian9, we are explicitly requesting to install Linux 4.9 with ABINAME=13. That stops on 4.9.228 while current Linux 4.9 is 4.9.240 bumped to ABI 14. Before ABI=13, we were requesting to install ABI=11 which stopped on 4.9.189 and was v↑'ed in 1f249bf7 (playbook: debian9: kernel v↑ (4.9.189-3 -> 4.9.228-1). In other words by explicitly specifying linux ABINAME we prevent to keep on updating Linux kernel to latest stable updates provided by upstream Linux and the distribution.
Another inconvenience of installing Linux with explicit ABINAME is interaction with nxd-fuse.ko: this module comes with nxd-fuse-dkms package, which uses dkms to build itself, and dkms recommends linux-headers-amd64 for modules that it manages to be able to build.
However we recently saw an issue when linux-headers-amd64 was installed as latest and depending on linux-headers-14-amd64 (NOTE ABINAME=14), while the kernel on that server was only linux-image-4.9.0-13-amd64 (NOTE ABINAME=13) as requested by our playbook. As the result nxd-fuse was skipped to compile, failed to be loaded and FUSE became non-working on that machine:
https://lab.nexedi.com/nexedi/slapos.package/merge_requests/132#note_120438
root@rapidspace-testnode-005:~# apt install nxd-fuse-dkms
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
nxd-fuse-dkms
0 upgraded, 1 newly installed, 0 to remove and 105 not upgraded.
Need to get 0 B/58.8 kB of archives.
After this operation, 295 kB of additional disk space will be used.
Selecting previously unselected package nxd-fuse-dkms.
(Reading database ... 80295 files and directories currently installed.)
Preparing to unpack .../nxd-fuse-dkms_4.9.nxd3+debian2_all.deb ...
Unpacking nxd-fuse-dkms (4.9.nxd3+debian2) ...
Setting up nxd-fuse-dkms (4.9.nxd3+debian2) ...
Loading new nxd-fuse-4.9.nxd3+debian2 DKMS files...
Building for 4.9.0-13-amd64
Module build for kernel 4.9.0-13-amd64 was skipped since the
kernel headers for this kernel does not seem to be installed.-> Fix it by requiring only linux-image-amd64 without specifying ABINAME and relying on upstream Linux and distro to provide stable updates for the kernel.