Re: [PATCH net-next] selftests: tls: size splice_short pipe by page size

[Nirmoy Das <nirmoyd@nvidia.com>]

On 24.06.26 15:51, Simon Horman wrote:
> On Mon, Jun 22, 2026 at 01:28:47PM -0700, Nirmoy Das wrote:
>> splice_short grows its pipe with (MAX_FRAGS + 1) * 0x1000 so it can
>> queue one short vmsplice() buffer for each fragment before draining the
>> pipe. That assumes 4K pipe buffers.
>>
>> On 64K-page kernels the request is rounded to 262144 bytes, which
>> provides only four pipe buffers. The fifth one-byte vmsplice() blocks in
>> pipe_wait_writable and the test times out before it reaches the TLS path.
>>
>> Request enough bytes for the same number of pipe buffers using the
>> runtime page size, and assert that the kernel granted at least that much.
>> If an unprivileged run cannot raise the pipe above the system
>> pipe-max-size limit, skip the test because it cannot exercise the
>> intended path.
>>
>> Fixes: 3667e9b442b9 ("selftests: tls: add test for short splice due to full skmsg")
>> Assisted-by: Codex:gpt-5
>> Signed-off-by: Nirmoy Das <nirmoyd@nvidia.com>
> The nit below not withstanding, this looks good to me.
>
> Reviewed-by: Simon Horman <horms@kernel.org>
>
>> ---
>>   tools/testing/selftests/net/tls.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/net/tls.c b/tools/testing/selftests/net/tls.c
>> index 30a236b8e9f73..e3bf4ade0f770 100644
>> --- a/tools/testing/selftests/net/tls.c
>> +++ b/tools/testing/selftests/net/tls.c
>> @@ -997,6 +997,8 @@ TEST_F(tls, splice_short)
>>   	char sendbuf[0x100];
>>   	char sendchar = 'S';
>>   	int pipefds[2];
>> +	int pipe_sz;
>> +	int ret;
>>   	int i;
>>   
>>   	sendchar_iov.iov_base = &sendchar;
>> @@ -1005,7 +1007,12 @@ TEST_F(tls, splice_short)
>>   	memset(sendbuf, 's', sizeof(sendbuf));
>>   
>>   	ASSERT_GE(pipe2(pipefds, O_NONBLOCK), 0);
>> -	ASSERT_GE(fcntl(pipefds[0], F_SETPIPE_SZ, (MAX_FRAGS + 1) * 0x1000), 0);
>> +	pipe_sz = (MAX_FRAGS + 1) * getpagesize();
>> +	ret = fcntl(pipefds[0], F_SETPIPE_SZ, pipe_sz);
>> +	if (ret < 0 && errno == EPERM)
>> +		SKIP(return, "insufficient pipe capacity");
>> +	ASSERT_GE(ret, 0);
> nit: the line above seems redundant to me given the line below.


Thanks Simon. Sent v2 with the nit addressed.


>
>> +	ASSERT_GE(ret, pipe_sz);
>>   
>>   	for (i = 0; i < MAX_FRAGS; i++)
>>   		ASSERT_GE(vmsplice(pipefds[1], &sendchar_iov, 1, 0), 0);
>> -- 
>> 2.43.0
>>