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ebd99a6b34
There are people building the module with M= that's supposed to be used
for external modules. This got broken in e9aa7c285d ("btrfs: enable
W=1 checks for btrfs").
$ make M=fs/btrfs
scripts/Makefile.lib:10: *** Recursive variable 'KBUILD_CFLAGS' references itself (eventually). Stop.
make: *** [Makefile:1755: modules] Error 2
There's a difference compared to 'make fs/btrfs/btrfs.ko' which needs
to rebuild a few more things and also the dependency modules need to be
available. It could fail with eg.
WARNING: Symbol version dump "Module.symvers" is missing.
Modules may not have dependencies or modversions.
In some environments it's more convenient to rebuild just the btrfs
module by M= so let's make it work.
The problem is with recursive variable evaluation in += so the
conditional C options are stored in a temporary variable to avoid the
recursion.
Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.