From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:35225 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725823AbhAMNST (ORCPT ); Wed, 13 Jan 2021 08:18:19 -0500 Subject: Re: [kvm-unit-tests PATCH v4 9/9] s390x: sclp: Add CPU entry offset comment References: <20210112132054.49756-1-frankja@linux.ibm.com> <20210112132054.49756-10-frankja@linux.ibm.com> <6f93c964-9606-246c-7266-85044803e49b@redhat.com> From: Thomas Huth Message-ID: Date: Wed, 13 Jan 2021 14:16:42 +0100 MIME-Version: 1.0 In-Reply-To: <6f93c964-9606-246c-7266-85044803e49b@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit List-ID: To: David Hildenbrand , Janosch Frank , kvm@vger.kernel.org Cc: borntraeger@de.ibm.com, imbrenda@linux.ibm.com, cohuck@redhat.com, linux-s390@vger.kernel.org On 13/01/2021 11.25, David Hildenbrand wrote: > On 12.01.21 14:20, Janosch Frank wrote: >> Let's make it clear that there is something at the end of the >> struct. The exact offset is reported by the cpu_offset member. >> >> Signed-off-by: Janosch Frank >> --- >> lib/s390x/sclp.h | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/lib/s390x/sclp.h b/lib/s390x/sclp.h >> index dccbaa8..395895f 100644 >> --- a/lib/s390x/sclp.h >> +++ b/lib/s390x/sclp.h >> @@ -134,7 +134,10 @@ typedef struct ReadInfo { >> uint8_t reserved7[134 - 128]; >> uint8_t byte_134_diag318 : 1; >> uint8_t : 7; >> - struct CPUEntry entries[0]; >> + /* >> + * The cpu entries follow, they start at the offset specified >> + * in offset_cpu. >> + */ > > I mean, that's just best practice. At least when I spot "[0];" and the > end of a struct, I know what's happening. > > No strong opinion about the comment, I wouldn't need it to understand it. The problem is that the "CPUEntry" entries either might be at this location, or later, so the entries[0] can be misleading. You always have to go via the offset_cpu field to find the right location. Thomas