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README.md

Motivation for metadata exctraction

Exporting documentation

This will allow us to build browseable documentation for the testcases, e.g. a catalogue of test information that would be searchable etc. At this point there is a single page generated from the extracted data that tries to outline the intent.

Propagating test requirements

Some subtests require differnt hardware resources/software versions/etc. the test execution framework needs to consume these so that it can locate proper hardware, install proper software, etc.

Some examples of requriments are:

  • Test needs at least 1GB of RAM.

  • Test needs a block device at least 512MB in size

  • Test needs a NUMA machine with two memory nodes and at least 300 free pages on each node

  • Test needs i2c eeprom connected on a i2c bus

  • Test needs two serial ports connected via null-modem cable

With this information extracted from the tests the testrunner can then map the requiremnts on the available machines in a lab and select a proper machine for the particular (sub)set of testcases as well as supply a particular test with additional information needed for the test, such as address of the i2c device, paths to the serial devices, etc. In the case of virtual machines the test could also dynamically prepare the correct environment for the test on demand.

Parallel test execution

An LTP testrun on a modern hardware wastes most of the machine resources because the testcases are running sequentially. However in order to execute tests in parallel we need to know which system resources are utilized by a given test, as obviously we cannot run two tests that monopolize the same resource.

Examples of such tests are:

  • Tests that mess with global system state

    • system time (e.g. settimeofday() test and leap second test)
    • SysV SHM
    • ...
  • Tests that use block device

  • Tests that work with a particular hardware resource

    • i2c eeprom test
    • serial port tests
    • ...

Exporting test runtime/timeout to the testrunner

Currently most of the testrunners usually do not know for how long is the test supposed to run, this means that we have to guess some upper limit on how long a test is supposed to run. The value is usually twice of the maximal runtime for all testcases or whole suite or even larger. This means that we are wasting time in the case that the test ends up stuck and we could have failed it much sooner in most of the cases. This becomes quite important for a kernel regression tests that do crash the host, if the information that the test is supposed to crash a kernel under a minute is exported to the testrunner we can reboot the machine much faster in an event of a crash.

Getting rid of runtest files

This would also allow us to get rid of the unflexible and hard to maintain runtest files. Once this system is in place we will have a list of all tests along with their respective metadata - which means that we will be able to generate subsets of the test easily on the fly.

In order to achieve this we need two things:

Each test will describe which syscall/functionality it tests in the metadata. Then we could define groups of tests based on that. I.e. instead of having syscall runtest file we would ask the testrunner to run all test that have a defined which syscall they test, or whose filename matches a particular syscall name.

Secondly we will have to store the test variants in the test metadata instead of putting them in a file that is unrelated to the test.

For example:

  • To run CVE related test we would select testcases with CVE tag

  • To run IPC test we will define a list of IPC syscalls and run all syscall test that are in the list

  • And many more...

Implementation

The docparser is implemented as a minimal C tokenizer that can parse and extract code comments and C structures. The docparser then runs over all C sources in the testcases directory and if tst_test structure is present in the source it's parsed and the result is included in the resulting metadata.

During parsing the metadata is stored in a simple key/value storage that more or less follows C structure layout, i.e. can include hash, array, and string. Once the parsing is finished the result is filtered so that only interesting fields of the tst_test structure are included and then converted into JSON output.

This process produces one big JSON file with metadata for all tests, that is then installed along with the testcases. This would then be used by the testrunner.

The test requirements are stored in the tst_test structure either as bitflags, integers or arrays of strings:

struct tst_test test = {
	...
	/* tests needs to run with UID=1 */
	.needs_root = 1,

	/*
	 * Tests needs a block device at least 1024MB in size and also
	 * mkfs.ext4 installed.
	 */
	.needs_device = 1,
	.dev_min_size = 1024,
	.dev_fs_type = ext4,

	/* Indicates that the test is messing with system wall clock */
	.restore_wallclock = 1,

	/* Tests needs uinput either compiled in or loaded as a module */
	.needs_drivers = (const char *[]) {
		"uinput",
		NULL
	},

	/* Tests needs enabled kernel config flags */
	.needs_kconfigs = (const char *[]) {
		"CONFIG_X86_INTEL_UMIP=y",
		NULL
	},

	/* Additional array of key value pairs */
	.tags = (const struct tst_tag[]) {
                {"linux-git", "43a6684519ab"},
                {"CVE", "2017-2671"},
                {NULL, NULL}
        }
};

The test documentation is stored in a special comment such as:

/*\
 * Test description
 *
 * This is a test description.
 * Consisting of several lines.
\*/

Which will yield following json output:

 "testcaseXY.c": {
  "needs_root": "1",
  "needs_device": "1",
  "dev_min_size": "1024",
  "dev_fs_type": "ext4",
  "restore_wallclock": "1",
  "needs_drivers": [
    "uinput",
    "NULL"
  ],
  "needs_kconfigs": [
    "CONFIG_X86_INTEL_UMIP=y",
    "NULL"
  ],
  "tags": [
    [
     "linux-git",
     "43a6684519ab"
    ],
    [
     "CVE",
     "2017-2671"
    ],
    [
     "NULL",
     "NULL"
    ]
   ],
  "doc": [
    " Test description",
    "",
    " This is a test description.",
    " Consisting of several lines."
  ],
  "fname": "testcases/kernel/syscalls/foo/testcaseXY.c"
 },

The final JSON file is an array of test descriptions such as this one.

Open Points

There are stil some loose ends. Mostly it's not well defined where to put things and how to format them.

  • Some of the hardware requirements are already listed in the tst_test. Should we put all of them there?

  • What would be the format for test documentation and how to store things such as test variants there?

So far this proof of concept generates a metadata file. I guess that we need actual consumers which will help to settle things down, I will try to look into making use of this in the runltp-ng at least as a reference implementation.

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