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([2a0d:3344:2712:7e10:4d59:d956:544f:d65c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4562e7f4294sm152558615e9.3.2025.07.21.01.45.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jul 2025 01:45:57 -0700 (PDT) Message-ID: <28bcda3f-52a9-43b9-86be-69e66b1f4ec2@redhat.com> Date: Mon, 21 Jul 2025 10:45:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v3 03/13] virtio: introduce extended features type To: Akihiko Odaki , qemu-devel@nongnu.org Cc: Paolo Bonzini , Dmitry Fleytman , Jason Wang , Sriram Yagnaraman , "Michael S. Tsirkin" , Stefano Garzarella , Cornelia Huck , Luigi Rizzo , Giuseppe Lettieri , Vincenzo Maffione , Eric Blake , Markus Armbruster References: <18dd4847-769f-4c5d-8559-8647822d362a@rsg.ci.i.u-tokyo.ac.jp> Content-Language: en-US From: Paolo Abeni In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pabeni@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.088, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=-1, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 7/21/25 9:49 AM, Akihiko Odaki wrote: > On 2025/07/21 16:33, Paolo Abeni wrote: >> On 7/20/25 12:41 PM, Akihiko Odaki wrote: >>> On 2025/07/18 17:52, Paolo Abeni wrote: >>>> diff --git a/include/hw/virtio/virtio-features.h b/include/hw/virtio/virtio-features.h >>>> new file mode 100644 >>>> index 0000000000..68e326e3e8 >>>> --- /dev/null >>>> +++ b/include/hw/virtio/virtio-features.h >>>> @@ -0,0 +1,123 @@ >>>> +/* >>>> + * Virtio features helpers >>>> + * >>>> + * Copyright 2025 Red Hat, Inc. >>>> + * >>>> + * SPDX-License-Identifier: GPL-2.0-or-later >>>> + */ >>>> + >>>> +#ifndef QEMU_VIRTIO_FEATURES_H >>>> +#define QEMU_VIRTIO_FEATURES_H >>>> + >>>> +#include "qemu/bitops.h" >>>> + >>>> +#define VIRTIO_FEATURES_FMT "%016"PRIx64"%016"PRIx64 >>>> +#define VIRTIO_FEATURES_PR(f) (f)[1], (f)[0] >>>> + >>>> +#define VIRTIO_FEATURES_MAX 128 >>>> +#define VIRTIO_BIT(b) BIT_ULL((b) % 64) >>>> +#define VIRTIO_DWORD(b) ((b) >> 6) >>>> +#define VIRTIO_FEATURES_WORDS (VIRTIO_FEATURES_MAX >> 5) >>>> +#define VIRTIO_FEATURES_DWORDS (VIRTIO_FEATURES_WORDS >> 1) >>> >>> These shifts are better to be replaced with division for clarity; >>> BIT_WORD() is a good example. >>> >>> "WORD" and "DWORD" should be avoided due to contradicting definitions >>> common in QEMU as described at: >>> https://lore.kernel.org/qemu-devel/aab8c434-364e-4305-9d8b-943eb0c98406@rsg.ci.i.u-tokyo.ac.jp/ >>> >>> BITS_TO_U32S() is a good example this regard. >> >> Ok, I'll rename: >> VIRTIO_FEATURES_DWORDS -> VIRTIO_U64_PER_FEATURES >> VIRTIO_FEATURES_WORDS -> VIRTIO_U32_PER_FEATURES > > U64 and U32 should be plural (i.e., rename them into > VIRTIO_U64S_PER_FEATURES and VIRTIO_U32S_PER_FEATURES) > > "PER_FEATURES" also sounds a bit awkward; BITS_PER_BYTE and > BITS_PER_LONG had singular after "per" so the unit was clear, but it is > not in this case. > > I could think of several options: > - VIRTIO_U64S_PER_FEATURES (what you proposed + plural U64S) > - VIRTIO_FEATURES_U64S (closer to the previous version) > - VIRTIO_FEATURES_NU64S (like CPU_TEMP_BUF_NLONGS) > - VIRTIO_U64S_PER_FEATURE_BITMASK > > They have downsides and upsides, and I don't have an idea what's the best. Indeed an optimal name here could be impossible to fit. IMHO VIRTIO_FEATURES_NU64S is the best option among the above and I like it. I'll use that one. Thanks, Paolo