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AHgh+RpWwZvjmmasCJknncEkqfZgJEjBldTX+bWl7F26Pe6vyUBzeJn5KcsjFP8OR0qUimOsQBQ0vzp/buo39DA=@vger.kernel.org X-Gm-Message-State: AOJu0YwzM+VNNTI1Y4rBSgsPBX/v9R9wfk+hb9LqVoE72NbUvBKcLAff j2Iy/oa8okrGsP/GnCX9sU0TDYMOkGWHg7MA/8UFXXPuZKdOM5JpQUhT9uF1qJ4aS5uNSAC45s/ v8QbhtBfHo4iEJUtjrxD8ZhmidSRxmdGRprWncVE= X-Gm-Gg: AfdE7ckvVyXiKLjycMn9D1tkfpjtsA17HtjFN4uoWNNF996HIoJo7+2tZTnbDfbLgiz OHlN9u2Rw39s1mLN3vj1y50JyGfRk7NRI4Q2gbCBLcRmCbDC3MvS41pF/Q4iSusFTgNHIG9sKRN wMNBK51G7xLNIf8nf0YNPEDER58SGXyHrnwHUTvDi/pGFjJwU8sB0XD7wgwM4kDFxv2zGzTkiu6 ne1j6cPSKBR0TvnPKVzKZCtmpKRICg6NTplcdxQD4C/ofx2tkgCJgbpxzSQInucpmzEDAU= X-Received: by 2002:a17:903:4b0c:b0:2bd:6dad:7ccd with SMTP id d9443c01a7336-2c99855966emr229385ad.25.1782489060232; Fri, 26 Jun 2026 08:51:00 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20260625202412.2986772-1-briandaniels@google.com> In-Reply-To: From: Brian Daniels Date: Fri, 26 Jun 2026 11:50:47 -0400 X-Gm-Features: AVVi8CcaG32oQ98-BwXSiQ-X6hlARwE9_bW6g1z1koV_pEWAyvNHcVBb8psrX4I Message-ID: Subject: Re: [PATCH v4 1/8] media: virtio: Add protocol To: "Bryan O'Donoghue" Cc: Mauro Carvalho Chehab , acourbot@google.com, adelva@google.com, aesteve@redhat.com, changyeon@google.com, daniel.almeida@collabora.com, eperezma@redhat.com, gnurou@gmail.com, gurchetansingh@google.com, hverkuil@xs4all.nl, jasowang@redhat.com, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, mst@redhat.com, nicolas.dufresne@collabora.com, virtualization@lists.linux.dev, xuanzhuo@linux.alibaba.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Jun 25, 2026 at 8:51=E2=80=AFPM Bryan O'Donoghue w= rote: > > On 25/06/2026 21:24, Brian Daniels wrote: > > I'm not an expert here, but taking a look at those files, the vast majo= rity of > > those reserved fields appear to be padding to ensure the struct has 64-= bit > > alignment, which matches the use here in virtio-media as well. > > > > virtio_pci appears to be the only device that explicitly states the > > reserved bytes are for future extensions. Unless there's a good a reaso= n to > > expect a future use case where more space is needed, I would prefer to = not add > > more at this time. > > I'm querying why just the one though ? Why not say four ? > > Perhaps something you could address in your commit log. > Sure I can add a note in v5. But yeah the reason is the total struct needs to be 64-bit aligned. So it can't be an arbitrary number. And all the current reserved fields add the minimum number of bits to ensure the existing structs are 64-bit aligned. Adding more means extra bytes are transferred every exchange without adding any value, which is inefficient.