'make srcdeb-pkg' generates a source package, which you can build
later by using dpkg-buildpackage.

In older dpkg versions, 'dpkg-buildpackage --jobs=N' sets not only
DEB_BUILD_OPTIONS but also MAKEFLAGS. Hence, passing -j or --jobs
to dpkg-buildpackage was enough for kicking the parallel execution.

The behavior was changed by commit 1d0ea9b2ba3f ("dpkg-buildpackage:
Change -j, --jobs semantics to non-force mode") of dpkg project. [1]

Since then, 'dpkg-buildpackage --jobs=N' sets only DEB_BUILD_OPTIONS,
which is not parsed by the current debian/rules. To build the package
in parallel, you need to pass the alternative --jobs-force option or
set the MAKEFLAGS environment variable.

Debian policy [2] suggests the following code snippet for debian/rules.

  ifneq (,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
      NUMJOBS = $(patsubst parallel=%,%,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
      MAKEFLAGS += -j$(NUMJOBS)
  endif

I tweaked the code to filter out parallel=1 and passed --jobs=1 to
dpkg-buildpackage from scripts/Makefile.package. It is needed to force
'make deb-pkg' without the -j option to run in serial. Please note that
dpkg-buildpackage sets parallel=<nproc> in DEB_BUILD_OPTIONS by default
(that is, --jobs=auto is the default) and --jobs=1 is needed to restore
the serial execution. When dpkg-buildpackage is invoked from Kbuild,
the number of jobs is inherited from the top level Makefile. Passing
--jobs=1 to dpkg-buildpackage allows debian/rules to skip parsing
DEB_BUILD_OPTIONS.

[1] https://salsa.debian.org/dpkg-team/dpkg/-/commit/1d0ea9b2ba3f6a2de5b1a6ff55f3df7b71f73db6
[2] https://www.debian.org/doc/debian-policy/ch-source.html#s-debianrules-options

Reported-by: Bastian Germann <bage@linutronix.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

debian/rules is generated by shell, but the escape sequence (\$) is
unreadable.

debian/rules embeds only two variables (ARCH and KERNELRELEASE).

Split them out to debian/rules.vars, and check-in the rest of Makefile
code to scripts/package/debian/rules.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Debian Policy "4.9. Main building script: debian/rules" requires
"debian/rules must start with the line #!/usr/bin/make -f". [1]

Currently, Kbuild does not follow this policy.

When Kbuild generates debian/rules, "#!$(command -v $MAKE) -f" is
expanded by shell. The resuling string may not be "#!/usr/bin/make -f".

There was a reason to opt out the Debian policy.

If you run '/path/to/my/custom/make deb-pkg', debian/rules must also be
invoked by the same Make program. If #!/usr/bin/make were hard-coded in
debian/rules, the sub-make would be executed by a possibly different
Make version.

This is problematic due to the MAKEFLAGS incompatibility, especially the
job server flag. Old Make versions used --jobserver-fds to propagate job
server file descriptors, but Make >= 4.2 uses --jobserver-auth. The flag
disagreement between the parent/child Makes would result in a process
fork explosion.

However, having a non-standard path in the shebang causes another issue;
the generated source package is not portable as such a path does not
exist in other build environments.

This commit solves those conflicting demands.

Hard-code '#!/usr/bin/make -f' in debian/rules to create a portable and
Debian-compliant source package.

Pass '--rules-file=$(MAKE) -f debian/rules' when dpkg-buildpackage is
invoked from Makefile so that debian/rules is executed by the same Make
program as used to start Kbuild.

[1] https://www.debian.org/doc/debian-policy/ch-source.html#main-building-script-debian-rules

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Merge the similar build targets.

Also, make the output location consistent.

Previously, source packages were created in the build directory,
while binary packages under ~/rpmbuild/RPMS/.

Now, Kbuild creates the rpmbuild/ directory in the build directory,
and saves all packages under it.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Most of the lines in the spec file are independent of any build
condition.

Split the body of the spec file into scripts/package/kernel.spec.
scripts/package/mkspec will prepend some env-dependent variables.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/package/mkspec preprocesses the spec file by sed, but it is
unreadable. This commit removes the last portion of the sed scripting.

Remove the $S$M prefixes from the conditionally generated lines.
Instead, surround the code with %if %{with_devel} ... %endif.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

For the same reason as commit 4243afdb9326 ("kbuild: builddeb: always
make modules_install, to install modules.builtin*"), run modules_install
even when CONFIG_MODULES=n to install modules.builtin*.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

To reduce the preprocess of the spec file, invoke the kernel build
from rpmbuild.

Run init/build-version to increment the release number not only for
binrpm-pkg but also for srcrpm-pkg and rpm-pkg.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

If this affects only %{buildroot}, it should be enough to use a fixed
string for _arch when it is undefined.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Avoid hard-coding the Version field in the generated spec file.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>