linux-kernel - Re: [PATCH v2 2/2] selftests/nolibc: add testcase for pipe

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Date:   Mon, 31 Jul 2023 20:28:44 +0200
From:   Thomas Weißschuh <thomas@...ch.de>
To:     Yuan Tan <tanyuan@...ylab.org>
Cc:     w@....eu, falcon@...ylab.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/2] selftests/nolibc: add testcase for pipe

On 2023-08-01 02:01:36+0800, Yuan Tan wrote:
> Hi Thomas,
> On Mon, 2023-07-31 at 17:41 +0200, Thomas Weißschuh wrote:
> > On 2023-07-31 20:35:28+0800, Yuan Tan wrote:
> > > On Mon, 2023-07-31 at 08:10 +0200, Thomas Weißschuh wrote:
> > > > On 2023-07-31 13:51:00+0800, Yuan Tan wrote:
> > > > > Add a testcase of pipe that child process sends message to
> > > > > parent
> > > > > process.
> > > > 
> > > > Thinking about it some more:
> > > > 
> > > > What's the advantage of going via a child process?
> > > > The pipe should work the same within the same process.
> > > > 
> > > 
> > > The pipe is commonly used for process communication, and I think as
> > > a
> > > test case it is supposed to cover the most common scenarios.
> > 
> > The testcase is supposed to cover the code of nolibc.
> > It should be the *minimal* amount of code to be reasonable sure that
> > the
> > code in nolibc does the correct thing.
> > If pipe() returns a value that behaves like a pipe I see no reason to
> > doubt it will also survive fork().
> > 
> > Validating that would mean testing the kernel and not nolibc.
> > For the kernel there are different testsuites.
> > 
> > Less code means less work for everyone involved, now and in the
> > future.
> > 
> 
> It's a good point and I never thought about this aspect.
> 
> I wonder whether the code below is enough?
> 
> static int test_pipe(void)
> {
> 	int pipefd[2];
> 
> 	if (pipe(pipefd) == -1)
> 		return 1;
> 
> 	close(pipefd[0]);
> 	close(pipefd[1]);
> 
> 	return 0;
> }

That is very barebones.

If accidentally a wrong syscall number was used and the used syscall
would not take any arguments this test would still succeed.

Keeping the write-read-cycle from the previous revision would test that
nicely. Essentially the same code as before but without the fork().

> 
> And I forgot to add this line:
> 
> 	CASE_TEST(pipe); EXPECT_SYSZR(1, test_pipe()); break;
> 
> I will add it in next patch.
>