This updates systemd to version v249.4 from version v247.6.

Besides the many new features that can be found in the upstream
repository they also introduced a bunch of cleanup which ended up
requiring a few more patches on our side.

a) 0022-core-Handle-lookup-paths-being-symlinks.patch:
  The way symlinked units were handled was changed in such that the last
  name of a unit file within one of the unit directories
  (/run/systemd/system, /etc/systemd/system, ...) is used as the name
  for the unit. Unfortunately that code didn't take into account that
  the unit directories themselves could already be symlinks and thus
  caused all our units to be recognized slightly different.

  There is an upstream PR for this new patch:
    systemd/systemd#20479

b) The way the APIVFS is setup has been changed in such a way that we
   now always have /run. This required a few changes to the
   confinement tests which did assert that they didn't exist. Instead of
   adding another patch we can just adopt the upstream behavior. An
   empty /run doesn't seem harmful.

   As part of this work I refactored the confinement test just a little
   bit to allow better debugging of test failures. Previously it would
   just fail at some point and it wasn't obvious which of the many
   commands failed or what the unexpected string was. This should now be
   more obvious.

c) Again related to the confinement tests the way a file was tested for
   being accessible was optimized. Previously systemd would in some
   situations open a file twice during that check. This was reduced to
   one operation but required the procfs to be mounted in a units
   namespace.

   An upstream bug was filed and fixed. We are now carrying the
   essential patch to fix that issue until it is backported to a new
   release (likely only version 250). The good part about this story is
   that upstream systemd now has a test case that looks very similar to
   one of our confinement tests. Hopefully that will lead to less
   friction in the long run.

   systemd/systemd#20514
   systemd/systemd#20515

d) Previously we could grep for dlopen( somewhat reliably but now
   upstream started using a wrapper around dlopen that is most of the
   time used with linebreaks. This makes using grep not ergonomic
   anymore.

   With this bump we are grepping for anything that looks like a
   dynamic library name (in contrast to a dlopen(3) call) and replace
   those instead. That seems more robust. Time will tell if this holds.

   I tried using coccinelle to patch all those call sites using its
   tooling but unfornately it does stumble upon the _cleanup_
   annotations that are very common in the systemd code.

e) We now have some machinery for libbpf support in our systemd build.
   That being said it doesn't actually work as generating some skeletons
   doesn't work just yet. It fails with the below error message and is
   disabled by default (in both minimal and the regular build).

   > FAILED: src/core/bpf/socket_bind/socket-bind.skel.h
   > /build/source/tools/build-bpf-skel.py --clang_exec /nix/store/x1bi2mkapk1m0zq2g02nr018qyjkdn7a-clang-wrapper-12.0.1/bin/clang --llvm_strip_exec /nix/store/zm0kqan9qc77x219yihmmisi9g3sg8ns-llvm-12.0.1/bin/llvm-strip --bpftool_exec /nix/store/l6dg8jlbh8qnqa58mshh3d8r6999dk0p-bpftools-5.13.11/bin/bpftool --arch x86_64 ../src/core/bpf/socket_bind/socket-bind.bpf.c src/core/bpf/socket_bind/socket-bind.skel.h
   > libbpf: elf: socket_bind_bpf is not a valid eBPF object file
   > Error: failed to open BPF object file: BPF object format invalid
   > Traceback (most recent call last):
   >   File "/build/source/tools/build-bpf-skel.py", line 128, in <module>
   >     bpf_build(args)
   >   File "/build/source/tools/build-bpf-skel.py", line 92, in bpf_build
   >     gen_bpf_skeleton(bpftool_exec=args.bpftool_exec,
   >   File "/build/source/tools/build-bpf-skel.py", line 63, in gen_bpf_skeleton
   >     skel = subprocess.check_output(bpftool_args, universal_newlines=True)
   >   File "/nix/store/81lwy2hfqj4c1943b1x8a0qsivjhdhw9-python3-3.9.6/lib/python3.9/subprocess.py", line 424, in check_output
   >     return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
   >   File "/nix/store/81lwy2hfqj4c1943b1x8a0qsivjhdhw9-python3-3.9.6/lib/python3.9/subprocess.py", line 528, in run
   >     raise CalledProcessError(retcode, process.args,
   > subprocess.CalledProcessError: Command '['/nix/store/l6dg8jlbh8qnqa58mshh3d8r6999dk0p-bpftools-5.13.11/bin/bpftool', 'g', 's', '../src/core/bpf/socket_bind/socket-bind.bpf.o']' returned non-zero exit status 255.
   > [102/1457] Compiling C object src/journal/libjournal-core.a.p/journald-server.c.oapture output)put)ut)
   > ninja: build stopped: subcommand failed.

  f) We do now have support for TPM2 based disk encryption in our
     systemd build. The actual bits and pieces to make use of that are
     missing but there are various ongoing efforts in that direction.
     There is also the story about systemd in our initrd to enable this
     being used for root volumes. None of this will yet work out of the
     box but we can start improving on that front.

  g) FIDO2 support was added systemd and consequently we can now use
     that. Just with TPM2 there hasn't been any integration work with
     NixOS and instead this just adds that capability to work on that.

Co-Authored-By: Jörg Thalheim <[email protected]>

This updates systemd to version v249.4 from version v247.6.

Besides the many new features that can be found in the upstream
repository they also introduced a bunch of cleanup which ended up
requiring a few more patches on our side.

a) 0022-core-Handle-lookup-paths-being-symlinks.patch:
  The way symlinked units were handled was changed in such that the last
  name of a unit file within one of the unit directories
  (/run/systemd/system, /etc/systemd/system, ...) is used as the name
  for the unit. Unfortunately that code didn't take into account that
  the unit directories themselves could already be symlinks and thus
  caused all our units to be recognized slightly different.

  There is an upstream PR for this new patch:
    systemd/systemd#20479

b) The way the APIVFS is setup has been changed in such a way that we
   now always have /run. This required a few changes to the
   confinement tests which did assert that they didn't exist. Instead of
   adding another patch we can just adopt the upstream behavior. An
   empty /run doesn't seem harmful.

   As part of this work I refactored the confinement test just a little
   bit to allow better debugging of test failures. Previously it would
   just fail at some point and it wasn't obvious which of the many
   commands failed or what the unexpected string was. This should now be
   more obvious.

c) Again related to the confinement tests the way a file was tested for
   being accessible was optimized. Previously systemd would in some
   situations open a file twice during that check. This was reduced to
   one operation but required the procfs to be mounted in a units
   namespace.

   An upstream bug was filed and fixed. We are now carrying the
   essential patch to fix that issue until it is backported to a new
   release (likely only version 250). The good part about this story is
   that upstream systemd now has a test case that looks very similar to
   one of our confinement tests. Hopefully that will lead to less
   friction in the long run.

   systemd/systemd#20514
   systemd/systemd#20515

d) Previously we could grep for dlopen( somewhat reliably but now
   upstream started using a wrapper around dlopen that is most of the
   time used with linebreaks. This makes using grep not ergonomic
   anymore.

   With this bump we are grepping for anything that looks like a
   dynamic library name (in contrast to a dlopen(3) call) and replace
   those instead. That seems more robust. Time will tell if this holds.

   I tried using coccinelle to patch all those call sites using its
   tooling but unfornately it does stumble upon the _cleanup_
   annotations that are very common in the systemd code.

e) We now have some machinery for libbpf support in our systemd build.
   That being said it doesn't actually work as generating some skeletons
   doesn't work just yet. It fails with the below error message and is
   disabled by default (in both minimal and the regular build).

   > FAILED: src/core/bpf/socket_bind/socket-bind.skel.h
   > /build/source/tools/build-bpf-skel.py --clang_exec /nix/store/x1bi2mkapk1m0zq2g02nr018qyjkdn7a-clang-wrapper-12.0.1/bin/clang --llvm_strip_exec /nix/store/zm0kqan9qc77x219yihmmisi9g3sg8ns-llvm-12.0.1/bin/llvm-strip --bpftool_exec /nix/store/l6dg8jlbh8qnqa58mshh3d8r6999dk0p-bpftools-5.13.11/bin/bpftool --arch x86_64 ../src/core/bpf/socket_bind/socket-bind.bpf.c src/core/bpf/socket_bind/socket-bind.skel.h
   > libbpf: elf: socket_bind_bpf is not a valid eBPF object file
   > Error: failed to open BPF object file: BPF object format invalid
   > Traceback (most recent call last):
   >   File "/build/source/tools/build-bpf-skel.py", line 128, in <module>
   >     bpf_build(args)
   >   File "/build/source/tools/build-bpf-skel.py", line 92, in bpf_build
   >     gen_bpf_skeleton(bpftool_exec=args.bpftool_exec,
   >   File "/build/source/tools/build-bpf-skel.py", line 63, in gen_bpf_skeleton
   >     skel = subprocess.check_output(bpftool_args, universal_newlines=True)
   >   File "/nix/store/81lwy2hfqj4c1943b1x8a0qsivjhdhw9-python3-3.9.6/lib/python3.9/subprocess.py", line 424, in check_output
   >     return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
   >   File "/nix/store/81lwy2hfqj4c1943b1x8a0qsivjhdhw9-python3-3.9.6/lib/python3.9/subprocess.py", line 528, in run
   >     raise CalledProcessError(retcode, process.args,
   > subprocess.CalledProcessError: Command '['/nix/store/l6dg8jlbh8qnqa58mshh3d8r6999dk0p-bpftools-5.13.11/bin/bpftool', 'g', 's', '../src/core/bpf/socket_bind/socket-bind.bpf.o']' returned non-zero exit status 255.
   > [102/1457] Compiling C object src/journal/libjournal-core.a.p/journald-server.c.oapture output)put)ut)
   > ninja: build stopped: subcommand failed.

  f) We do now have support for TPM2 based disk encryption in our
     systemd build. The actual bits and pieces to make use of that are
     missing but there are various ongoing efforts in that direction.
     There is also the story about systemd in our initrd to enable this
     being used for root volumes. None of this will yet work out of the
     box but we can start improving on that front.

  g) FIDO2 support was added systemd and consequently we can now use
     that. Just with TPM2 there hasn't been any integration work with
     NixOS and instead this just adds that capability to work on that.

Co-Authored-By: Jörg Thalheim <[email protected]>