[libc] implement pipe2

[michaelrj-google]

The pipe2 is defined on linux here: https://man7.org/linux/man-pages/man2/pipe.2.html

This is a simple syscall wrapper, so implementation should be straightforward.

Build System

In entrypoints.txt

• Add the new function to the list of entrypoints for unistd.h (you need to do this before it will build)

In unistd/CMakeLists.txt

• Add new entrypoint objects to the list
• Also add it to the list for unistd/linux/CMakeLists.txt

In linux.td

• Add the functions to the list of functions for unistd.h (this can be confusing, ask for help if you're stuck).

Code

Create unistd/pipe2.h

• look at dup.h for an example of how this should be laid out (copying the whole file and modifying it is fine).

Create unistd/linux/pipe2.cpp

• Again, look at look at linux/dup.cpp for an example.

Testing

Create test/src/unistd/pipe2_test.cpp

• This needs to test the function succeeding and failing
• This is only testing the code you wrote, so don't worry too much about testing parts of the interface that the kernel handles.

Add your tests to test/src/unistd/CMakeLists.txt

• Hopefully self-explanatory

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. In the comments of the issue, request for it to be assigned to you.
2. Fix the issue locally.
3. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
4. Create a Git commit.
5. Run git clang-format HEAD~1 to format your changes.
6. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Michael Jones (michaelrj-google)

The pipe2 is defined on linux here: https://man7.org/linux/man-pages/man2/pipe.2.html

This is a simple syscall wrapper, so implementation should be straightforward.

Build System

In entrypoints.txt

• Add the new function to the list of entrypoints for unistd.h (you need to do this before it will build)

In unistd/CMakeLists.txt

• Add new entrypoint objects to the list
• Also add it to the list for unistd/linux/CMakeLists.txt

In linux.td

• Add the functions to the list of functions for unistd.h (this can be confusing, ask for help if you're stuck).

Code

Create unistd/pipe2.h

• look at dup.h for an example of how this should be laid out (copying the whole file and modifying it is fine).

Create unistd/linux/pipe2.cpp

• Again, look at look at linux/dup.cpp for an example.

Testing

Create test/src/unistd/pipe2_test.cpp

• This needs to test the function succeeding and failing
• This is only testing the code you wrote, so don't worry too much about testing parts of the interface that the kernel handles.

Add your tests to test/src/unistd/CMakeLists.txt

• Hopefully self-explanatory

[llvmbot]

@llvm/issue-subscribers-libc

Author: Michael Jones (michaelrj-google)

The pipe2 is defined on linux here: https://man7.org/linux/man-pages/man2/pipe.2.html

This is a simple syscall wrapper, so implementation should be straightforward.

Build System

In entrypoints.txt

• Add the new function to the list of entrypoints for unistd.h (you need to do this before it will build)

In unistd/CMakeLists.txt

• Add new entrypoint objects to the list
• Also add it to the list for unistd/linux/CMakeLists.txt

In linux.td

• Add the functions to the list of functions for unistd.h (this can be confusing, ask for help if you're stuck).

Code

Create unistd/pipe2.h

• look at dup.h for an example of how this should be laid out (copying the whole file and modifying it is fine).

Create unistd/linux/pipe2.cpp

• Again, look at look at linux/dup.cpp for an example.

Testing

Create test/src/unistd/pipe2_test.cpp

• This needs to test the function succeeding and failing
• This is only testing the code you wrote, so don't worry too much about testing parts of the interface that the kernel handles.

Add your tests to test/src/unistd/CMakeLists.txt

• Hopefully self-explanatory

[muffpy]

Interested

[muffpy]

@michaelrj-google Under build system, did you mean add the function spec for pipe2 to posix.td? I don't see a header spec for unistd.h in linux.td.

[michaelrj-google]

I did mean to put it in linux.td since it's specifically a linux function and not in posix. If there isn't a unistd.h HeaderSpec in linux.td yet then you'll have to create a new one and add it to the list of headers at the bottom.

[muffpy]

@michaelrj-google Should this HeaderSpec in linux.td contain FunctionSpecs for every syscall in libc/src/unistd/ or just for pipe2?

[michaelrj-google]

just pipe2 is fine for the moment

[muffpy]

@michaelrj-google I am unable to generate the test file for pipe2_test.cpp. I have tried:

$ cmake ../llvm -G Ninja -DLLVM_ENABLE_PROJECTS="libc"  -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
$ ninja libc_unistd_unittests

but the output does not show a test for pipe2.

Please take a look at my patch 85514.

[duncpro]

If @muffpy isn't working on this anymore I'd like to give it a go.

[nickdesaulniers]

All yours @duncpro . Reassigning.