[Bug 1833586] Re: open-iscsi unconditionally requires ib_iser module which is not built on all Ubuntu kernels

[Steve Langasek]

After discussing with Ryan on IRC:

 - the static loading of the modules is bad, and shouldn't be necessary, as it should be possible to figure out at runtime which transports are actually needed by iscsid
 - the current implementation doesn't work in the initramfs at all since the file it creates is only read by systemd
 - upstream's code has support for loading these modules on-demand, *IF* we link against libkmod.

Proposed solution:

 - Build-depend on libkmod-dev
 - Drop the file for loading modules statically
 - Add ib_iser to the list of modules for the initramfs hook, so that iscsi rootfs will work correctly over infiniband as well

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https://bugs.launchpad.net/bugs/1833586

Title:
  open-iscsi unconditionally requires ib_iser module which is not built
  on all Ubuntu kernels

Status in open-iscsi package in Ubuntu:
  New

Bug description:
  Currently, open-iscsi ships a /lib/modules-load.d/open-iscsi.conf
  which hard-codes the iscsi_tcp and ib_iser modules.  However, we ship
  open-iscsi as part of the standard ubuntu-server seed, but not all
  images that derive from this seed have kernels that include the
  ib_iser module.  In particular, we've noticed that the Raspberry Pi
  kernel does not.  This is noticeable because if a module doesn't
  exist, the systemd-modules-load service fails, and leaves the system
  boot in a degraded mode per systemd.

  And unfortunately ib_iser has no modaliases, so it's not as if this is
  something that can be switched to udev autoloading.

  Options for resolving this:

   - get the kernel team to set CONFIG_INFINIBAND_ISER=m on all kernels.  But this would increase kernel memory consumption unconditionally on possibly memory-constrained arm systems, for no real value.  (A spot check on another arch shows roughly 750K; not huge but not nothing)
   - drop ib_iser from debian/open-iscsi.kmod (why does use of iscsi dictate loading a particular infiniband module? there's nothing in the debian/changelog that explains)
   - vary the contents of /lib/modules-load.d/open-iscsi.conf (only sensible if we believe that this module would never be useful on any armhf)
   - remove open-iscsi from the server seed; historically, this is blocked by older versions of MAAS depending on mounting ephemeral images via iscsi, but perhaps the depends on open-iscsi could be made architecture-dependent, if only armhf is affected by this problem and MAAS doesn't support any armhf targets?

  This needs input from the Server Team.

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