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The test harness forks() a child to run each test. Both the parent and the child print to stdout using libc functions. That can lead to duplicated (or more) output if the libc buffers are not flushed before forking. It's generally not seen when running programs directly, because stdout will usually be line buffered when it's pointing to a terminal. This was noticed when running the seccomp_bpf test, eg: $ ./seccomp_bpf | tee test.log $ grep -c "TAP version 13" test.log 2 But we only expect the TAP header to appear once. It can be exacerbated using stdbuf to increase the buffer size: $ stdbuf -o 1MB ./seccomp_bpf > test.log $ grep -c "TAP version 13" test.log 13 The fix is simple, we just flush stdout & stderr before fork. Usually stderr is unbuffered, but that can be changed, so flush it as well just to be safe. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Tested-by: Max Filippov <jcmvbkbc@gmail.com> Acked-by: Shuah Khan <skhan@linuxfoundation.org> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.