memblock tests: Add TODO and README files

Add description of the project, its structure and how to run it.
List what is left to implement and what the known issues are.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/d5e39b9f7dcef177ebc14282727447bc21e3b38f.1646055639.git.karolinadrobnik@gmail.com

Author: drobnik

tools/testing/memblock/README

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+==================
+Memblock simulator
+==================
+
+Introduction
+============
+
+Memblock is a boot time memory allocator[1] that manages memory regions before
+the actual memory management is initialized. Its APIs allow to register physical
+memory regions, mark them as available or reserved, allocate a block of memory
+within the requested range and/or in specific NUMA node, and many more.
+
+Because it is used so early in the booting process, testing and debugging it is
+difficult. This test suite, usually referred as memblock simulator, is
+an attempt at testing the memblock mechanism. It runs one monolithic test that
+consist of a series of checks that exercise both the basic operations and
+allocation functionalities of memblock. The main data structure of the boot time
+memory allocator is initialized at the build time, so the checks here reuse its
+instance throughout the duration of the test. To ensure that tests don't affect
+each other, region arrays are reset in between.
+
+As this project uses the actual memblock code and has to run in user space,
+some of the kernel definitions were stubbed by the initial commit that
+introduced memblock simulator (commit 16802e55dea9 ("memblock tests: Add
+skeleton of the memblock simulator")) and a few preparation commits just
+before it. Most of them don't match the kernel implementation, so one should
+consult them first before making any significant changes to the project.
+
+Usage
+=====
+
+To run the tests, build the main target and run it:
+
+$ make && ./main
+
+A successful run produces no output. It is also possible to override different
+configuration parameters. For example, to simulate enabled NUMA, use:
+
+$ make NUMA=1
+
+For the full list of options, see `make help`.
+
+Project structure
+=================
+
+The project has one target, main, which calls a group of checks for basic and
+allocation functions. Tests for each group are defined in dedicated files, as it
+can be seen here:
+
+memblock
+|-- asm       ------------------,
+|-- lib                         |-- implement function and struct stubs
+|-- linux     ------------------'
+|-- scripts
+|    |-- Makefile.include        -- handles `make` parameters
+|-- tests
+|    |-- alloc_api.(c|h)         -- memblock_alloc tests
+|    |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests
+|    |-- alloc_nid_api.(c|h)     -- memblock_alloc_try_nid tests
+|    |-- basic_api.(c|h)         -- memblock_add/memblock_reserve/... tests
+|    |-- common.(c|h)            -- helper functions for resetting memblock;
+|-- main.c        --------------.   dummy physical memory definition
+|-- Makefile                     `- test runner
+|-- README
+|-- TODO
+|-- .gitignore
+
+Simulating physical memory
+==========================
+
+Some allocation functions clear the memory in the process, so it is required for
+memblock to track valid memory ranges. To achieve this, the test suite registers
+with memblock memory stored by test_memory struct. It is a small wrapper that
+points to a block of memory allocated via malloc. For each group of allocation
+tests, dummy physical memory is allocated, added to memblock, and then released
+at the end of the test run. The structure of a test runner checking allocation
+functions is as follows:
+
+int memblock_alloc_foo_checks(void)
+{
+	reset_memblock_attributes();     /* data structure reset */
+	dummy_physical_memory_init();    /* allocate and register memory */
+
+	(...allocation checks...)
+
+	dummy_physical_memory_cleanup(); /* free the memory */
+}
+
+There's no need to explicitly free the dummy memory from memblock via
+memblock_free() call. The entry will be erased by reset_memblock_regions(),
+called at the beginning of each test.
+
+Known issues
+============
+
+1. Requesting a specific NUMA node via memblock_alloc_node() does not work as
+   intended. Once the fix is in place, tests for this function can be added.
+
+2. Tests for memblock_alloc_low() can't be easily implemented. The function uses
+   ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low
+   memory of the memory_block.
+
+References
+==========
+
+1. Boot time memory management documentation page:
+   https://www.kernel.org/doc/html/latest/core-api/boot-time-mm.html

tools/testing/memblock/TODO

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+TODO
+=====
+
+1. Add verbose output (e.g., what is being tested and how many tests cases are
+   passing)
+
+2. Add flags to Makefile:
+   + verbosity level
+   + enable memblock_dbg() messages (i.e. pass "-D CONFIG_DEBUG_MEMORY_INIT"
+     flag)
+
+3. Add tests trying to memblock_add() or memblock_reserve() 129th region.
+   This will trigger memblock_double_array(), make sure it succeeds.
+   *Important:* These tests require valid memory ranges, use dummy physical
+                memory block from common.c to implement them. It is also very
+                likely that the current MEM_SIZE won't be enough for these
+                test cases. Use realloc to adjust the size accordingly.
+
+4. Add test cases using this functions (implement them for both directions):
+   + memblock_alloc_raw()
+   + memblock_alloc_exact_nid_raw()
+   + memblock_alloc_try_nid_raw()
+
+5. Add tests for memblock_alloc_node() to check if the correct NUMA node is set
+   for the new region
+
+6. Update comments in tests/basic_api.c to match the style used in
+   tests/alloc_*.c