Add FUSE integration test

This commit adds an integration test framework for FUSE support. Please
refer to the test example and test/fuse/README.md for further details.

Fixes #3098

1 files changed, 102 insertions, 0 deletions

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+# gVisor FUSE Test Suite
+
+This is an integration test suite for fuse(4) filesystem. It runs under both
+gVisor and Linux, and ensures compatibility between the two. This test suite is
+based on system calls test.
+
+This document describes the framework of fuse integration test and the
+guidelines that should be followed when adding new fuse tests.
+
+## Integration Test Framework
+
+Please refer to the figure below. `>` is entering the function, `<` is leaving
+the function, and `=` indicates sequentially entering and leaving.
+
+```
+ |  Client (Test Main Process)         |  Server (FUSE Daemon)
+ |                                     |
+ |  >TEST_F()                          |
+ |    >SetUp()                         |
+ |      =MountFuse()                   |
+ |      >SetUpFuseServer()             |
+ |        [create communication pipes] |
+ |        =fork()                      |        =fork()
+ |        >WaitCompleted()             |
+ |          [wait for MarkDone()]      |
+ |                                     |        =ConsumeFuseInit()
+ |                                     |        =MarkDone()
+ |        <WaitCompleted()             |
+ |      <SetUpFuseServer()             |
+ |    <SetUp()                         |
+ |    >SetExpected()                   |
+ |      [construct expected reaction]  |
+ |                                     |        >FuseLoop()
+ |                                     |          >ReceiveExpected()
+ |                                     |            [wait data from pipe]
+ |      [write data to pipe]           |
+ |      [wait for MarkDone()]          |
+ |                                     |            [save data to memory]
+ |                                     |            =MarkDone()
+ |    <SetExpected()                   |
+ |                                     |          <ReceiveExpected()
+ |                                     |          >read()
+ |                                     |            [wait for fs operation]
+ |    >[Do fs operation]               |
+ |      [wait for fs response]         |
+ |                                     |          <read()
+ |                                     |          =CompareRequest()
+ |                                     |          =write() [write fs response]
+ |    <[Do fs operation]               |
+ |    =[Test fs operation result]      |
+ |    =[wait for MarkDone()]           |
+ |                                     |          =MarkDone()
+ |    >TearDown()                      |
+ |      =UnmountFuse()                 |
+ |    <TearDown()                      |
+ |  <TEST_F()                          |
+```
+
+## Running the tests
+
+Based on syscall tests, fuse tests can run in different environments. To enable
+fuse testing environment, the test targets should be appended with `_fuse`.
+
+For example, to run fuse test in `stat_test.cc`:
+
+```bash
+$ bazel test //test/fuse:stat_test_runsc_ptrace_vfs2_fuse
+```
+
+Test all targets tagged with fuse:
+
+```bash
+$ bazel test --test_tag_filters=fuse //test/fuse/...
+```
+
+## Writing a new FUSE test
+
+1. Add test targets in `BUILD` and `linux/BUILD`.
+2. Inherit your test from `FuseTest` base class. It allows you to:
+  - Run a fake FUSE server in background during each test setup.
+  - Create pipes for communication and provide utility functions.
+  - Stop FUSE server after test completes.
+3. Customize your comparison function for request assessment in FUSE server.
+4. Add the mapping of the size of structs if you are working on new FUSE opcode.
+  - Please update `FuseTest::GetPayloadSize()` for each new FUSE opcode.
+5. Build the expected request-response pair of your FUSE operation.
+6. Call `SetExpected()` function to inject the expected reaction.
+7. Check the response and/or errors.
+8. Finally call `WaitCompleted()` to ensure the FUSE server acts correctly.
+
+A few customized matchers used in syscalls test are encouraged to test the
+outcome of filesystem operations. Such as:
+
+```cc
+SyscallSucceeds()
+SyscallSucceedsWithValue(...)
+SyscallFails()
+SyscallFailsWithErrno(...)
+```
+
+Please refer to [test/syscalls/README.md](../syscalls/README.md) for further
+details.