forked from Minki/linux
6bc756193f
'libnvdimm' is the first driver sub-system in the kernel to implement mocking for unit test coverage. The nfit_test module gets built as an external module and arranges for external module replacements of nfit, libnvdimm, nd_pmem, and nd_blk. These replacements use the linker --wrap option to redirect calls to ioremap() + request_mem_region() to custom defined unit test resources. The end result is a fully functional nvdimm_bus, as far as userspace is concerned, but with the capability to perform otherwise destructive tests on emulated resources. Q: Why not use QEMU for this emulation? QEMU is not suitable for unit testing. QEMU's role is to faithfully emulate the platform. A unit test's role is to unfaithfully implement the platform with the goal of triggering bugs in the corners of the sub-system implementation. As bugs are discovered in platforms, or the sub-system itself, the unit tests are extended to backstop a fix with a reproducer unit test. Another problem with QEMU is that it would require coordination of 3 software projects instead of 2 (kernel + libndctl [1]) to maintain and execute the tests. The chances for bit rot and the difficulty of getting the tests running goes up non-linearly the more components involved. Q: Why submit this to the kernel tree instead of external modules in libndctl? Simple, to alleviate the same risk that out-of-tree external modules face. Updates to drivers/nvdimm/ can be immediately evaluated to see if they have any impact on tools/testing/nvdimm/. Q: What are the negative implications of merging this? It is a unique maintenance burden because the purpose of mocking an interface to enable a unit test is to purposefully short circuit the semantics of a routine to enable testing. For example __wrap_ioremap_cache() fakes the pmem driver into "ioremap()'ing" a test resource buffer allocated by dma_alloc_coherent(). The future maintenance burden hits when someone changes the semantics of ioremap_cache() and wonders what the implications are for the unit test. [1]: https://github.com/pmem/ndctl Cc: <linux-acpi@vger.kernel.org> Cc: Lv Zheng <lv.zheng@intel.com> Cc: Robert Moore <robert.moore@intel.com> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
41 lines
1.1 KiB
Makefile
41 lines
1.1 KiB
Makefile
ldflags-y += --wrap=ioremap_cache
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ldflags-y += --wrap=ioremap_nocache
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ldflags-y += --wrap=iounmap
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ldflags-y += --wrap=__request_region
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ldflags-y += --wrap=__release_region
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DRIVERS := ../../../drivers
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NVDIMM_SRC := $(DRIVERS)/nvdimm
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ACPI_SRC := $(DRIVERS)/acpi
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obj-$(CONFIG_LIBNVDIMM) += libnvdimm.o
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obj-$(CONFIG_BLK_DEV_PMEM) += nd_pmem.o
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obj-$(CONFIG_ND_BTT) += nd_btt.o
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obj-$(CONFIG_ND_BLK) += nd_blk.o
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obj-$(CONFIG_ACPI_NFIT) += nfit.o
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nfit-y := $(ACPI_SRC)/nfit.o
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nfit-y += config_check.o
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nd_pmem-y := $(NVDIMM_SRC)/pmem.o
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nd_pmem-y += config_check.o
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nd_btt-y := $(NVDIMM_SRC)/btt.o
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nd_btt-y += config_check.o
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nd_blk-y := $(NVDIMM_SRC)/blk.o
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nd_blk-y += config_check.o
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libnvdimm-y := $(NVDIMM_SRC)/core.o
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libnvdimm-y += $(NVDIMM_SRC)/bus.o
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libnvdimm-y += $(NVDIMM_SRC)/dimm_devs.o
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libnvdimm-y += $(NVDIMM_SRC)/dimm.o
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libnvdimm-y += $(NVDIMM_SRC)/region_devs.o
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libnvdimm-y += $(NVDIMM_SRC)/region.o
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libnvdimm-y += $(NVDIMM_SRC)/namespace_devs.o
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libnvdimm-y += $(NVDIMM_SRC)/label.o
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libnvdimm-$(CONFIG_BTT) += $(NVDIMM_SRC)/btt_devs.o
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libnvdimm-y += config_check.o
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obj-m += test/
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