From: Brian Daniels <briandaniels@google.com>
To: "Bryan O'Donoghue" <bod@kernel.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Brian Daniels <briandaniels@google.com>,
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
Subject: Re: [PATCH v4 1/8] media: virtio: Add protocol
Date: Thu, 25 Jun 2026 16:24:03 -0400 [thread overview]
Message-ID: <20260625202412.2986772-1-briandaniels@google.com> (raw)
In-Reply-To: <4b2078a0-9422-467b-b167-9a0b5444f18d@kernel.org>
> > + u32 __reserved;
>
> Knowing ~ nothing about virtio with ~ no experience of it I'll offer up
> a question/statement anyway.
>
> Aren't your reservations here a bit conservative ? Would you not be well
> advised to reserve a bit more space per other virtio protocols ?
>
> ➜ grep reserved ./include/uapi/linux/*.h | grep virtio
> ./include/uapi/linux/virtio_balloon.h: * __u8 reserved[6];
> ./include/uapi/linux/virtio_balloon.h: * In other words, add explicit
> reserved fields to align field and
> ./include/uapi/linux/virtio_blk.h: __u8 reserved[38];
> ./include/uapi/linux/virtio_blk.h: __u8 reserved[56];
> ./include/uapi/linux/virtio_config.h: * VIRTIO_TRANSPORT_F_END are
> reserved for the transport
> ./include/uapi/linux/virtio_crypto.h: __le32 reserved;
> ./include/uapi/linux/virtio_i2c.h: * Copyright (c) 2021 Intel
> Corporation. All rights reserved.
> ./include/uapi/linux/virtio_input.h: __u8 reserved[5];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[3];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[3];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[3];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[4];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[8];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[4];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[3];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[64];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved[3];
> ./include/uapi/linux/virtio_iommu.h: __u8
> reserved2[4];
> ./include/uapi/linux/virtio_net.h: __le16 reserved[4];
> ./include/uapi/linux/virtio_net.h: __le16 reserved;
> ./include/uapi/linux/virtio_net.h: __le16 reserved[3];
> ./include/uapi/linux/virtio_net.h: __u8 reserved;
> ./include/uapi/linux/virtio_net.h: __le16 reserved1;
> ./include/uapi/linux/virtio_pcidev.h: * @VIRTIO_PCIDEV_OP_RESERVED:
> reserved to catch errors
> ./include/uapi/linux/virtio_pcidev.h: * @reserved: reserved
> ./include/uapi/linux/virtio_pcidev.h: __u16 reserved;
> ./include/uapi/linux/virtio_pci.h: * 2-65535 - reserved
> ./include/uapi/linux/virtio_pci.h: /* Unused, reserved for future
> extensions. */
> ./include/uapi/linux/virtio_pci.h: __u8 reserved1[12];
> ./include/uapi/linux/virtio_pci.h: /* Unused, reserved for future
> extensions. */
> ./include/uapi/linux/virtio_pci.h: __u8 reserved2[4];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[2];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_pci.h: __u8 reserved;
> ./include/uapi/linux/virtio_pci.h: __le32 reserved;
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_pci.h: __le32 reserved;
> ./include/uapi/linux/virtio_pci.h: __le32 reserved;
> ./include/uapi/linux/virtio_pci.h: __le32 reserved;
> ./include/uapi/linux/virtio_pci.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_rtc.h: * Copyright (c) 2024 Qualcomm
> Innovation Center, Inc. All rights reserved.
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[5];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[5];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[5];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[7];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[5];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[5];
> ./include/uapi/linux/virtio_rtc.h: __u8 reserved[6];
> ./include/uapi/linux/virtio_spi.h: * Copyright (C) 2025 Qualcomm
> Innovation Center, Inc. All rights reserved.
> ./include/uapi/linux/virtio_spi.h: * other bits are reserved as 0,
> 1-bit transfer is always supported.
> ./include/uapi/linux/virtio_spi.h: * other bits are reserved as 0,
> 1-bit transfer is always supported.
> ./include/uapi/linux/virtio_spi.h: * @reserved: for future use.
> ./include/uapi/linux/virtio_spi.h: __u8 reserved[3];+ u32
> __reserved;
I'm not an expert here, but taking a look at those files, the vast majority 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 reason to
expect a future use case where more space is needed, I would prefer to not add
more at this time.
next prev parent reply other threads:[~2026-06-25 20:24 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-22 20:43 [PATCH v4 0/8] media: add virtio-media driver Brian Daniels
2026-06-22 20:43 ` [PATCH v4 1/8] media: virtio: Add protocol Brian Daniels
2026-06-22 21:05 ` Michael S. Tsirkin
2026-06-25 19:50 ` Brian Daniels
2026-06-23 0:57 ` Bryan O'Donoghue
2026-06-25 20:24 ` Brian Daniels [this message]
2026-06-26 0:50 ` Bryan O'Donoghue
2026-06-26 15:50 ` Brian Daniels
2026-07-12 7:28 ` Mauro Carvalho Chehab
2026-06-22 20:43 ` [PATCH v4 2/8] media: virtio: Add virtio-media driver structs and function declarations Brian Daniels
2026-06-22 21:08 ` Michael S. Tsirkin
2026-07-17 19:46 ` Brian Daniels
2026-06-23 1:09 ` Bryan O'Donoghue
2026-06-25 20:25 ` Brian Daniels
2026-06-22 20:43 ` [PATCH v4 3/8] media: virtio: Add virtio-media session related structures Brian Daniels
2026-06-22 20:43 ` [PATCH v4 4/8] media: virtio: Add scatterlist_builder Brian Daniels
2026-06-22 20:43 ` [PATCH v4 5/8] media: virtio: Add virtio_media_ioctls Brian Daniels
2026-06-22 20:43 ` [PATCH v4 6/8] media: virtio: Add virtio_media_driver Brian Daniels
2026-06-22 21:21 ` Michael S. Tsirkin
2026-06-25 20:18 ` Brian Daniels
2026-07-12 6:57 ` Mauro Carvalho Chehab
2026-07-17 20:58 ` Brian Daniels
2026-06-26 13:33 ` Markus Elfring
2026-06-22 20:43 ` [PATCH v4 7/8] media: virtio: Add virtio-media to the build system Brian Daniels
2026-06-22 20:43 ` [PATCH v4 8/8] media: virtio: Add MAINTAINERS entry Brian Daniels
2026-06-22 21:23 ` Michael S. Tsirkin
2026-06-25 20:20 ` Brian Daniels
2026-06-22 21:09 ` [PATCH v4 0/8] media: add virtio-media driver Michael S. Tsirkin
2026-06-25 20:21 ` Brian Daniels
2026-07-10 20:44 ` Brian Daniels
2026-07-11 9:02 ` Michael S. Tsirkin
2026-07-12 7:10 ` Mauro Carvalho Chehab
2026-07-13 7:00 ` Albert Esteve
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