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Date: Tue, 28 May 2019 14:11:48 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: building individual files in subdirectories
Message-ID: <20190528121148.GA18162@lst.de>
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Sender: linux-kbuild-owner@vger.kernel.org
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To: linux-kbuild@vger.kernel.org

A few kernel modules have source files in multiple subdirectories.
Trying to build just a single object of a source file in such a
subdirectory currently doesn't work.

For example:

hch@brick:~/work/xfs$ make fs/xfs/libxfs/xfs_alloc.o
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
scripts/Makefile.build:42: fs/xfs/libxfs/Makefile: No such file or directory
make[1]: *** No rule to make target 'fs/xfs/libxfs/Makefile'.  Stop.
make: *** [Makefile:1747: fs/xfs/libxfs/xfs_alloc.o] Error 2

Is there any reasonably easy way to get this to work?