Re: [PATCH v3 01/17] virtio_pci: struct virtio_pci_common_cfg add queue_notify_data

On Tue, Feb 8, 2022 at 11:29 AM Xuan Zhuo [off-list ref] wrote:

On Tue, 8 Feb 2022 11:24:13 +0800, Jason Wang [off-list ref] wrote:

quoted

On Tue, Feb 8, 2022 at 11:20 AM Xuan Zhuo [off-list ref] wrote:

quoted

On Tue, 8 Feb 2022 11:03:17 +0800, Jason Wang [off-list ref] wrote:

quoted

On Tue, Feb 8, 2022 at 10:17 AM Xuan Zhuo [off-list ref] wrote:

quoted

On Mon, 7 Feb 2022 16:06:15 +0800, Jason Wang [off-list ref] wrote:

quoted

On Mon, Feb 7, 2022 at 2:07 PM Xuan Zhuo [off-list ref] wrote:

quoted

On Mon, 7 Feb 2022 11:41:06 +0800, Jason Wang [off-list ref] wrote:

quoted

在 2022/1/26 下午3:35, Xuan Zhuo 写道:

quoted

Add queue_notify_data in struct virtio_pci_common_cfg, which comes from
here https://github.com/oasis-tcs/virtio-spec/issues/89

Since I want to add queue_reset after it, I submitted this patch first.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
  include/uapi/linux/virtio_pci.h | 1 +
  1 file changed, 1 insertion(+)

diff --git a/include/uapi/linux/virtio_pci.h b/include/uapi/linux/virtio_pci.h
index 3a86f36d7e3d..492c89f56c6a 100644
--- a/include/uapi/linux/virtio_pci.h
+++ b/include/uapi/linux/virtio_pci.h

@@ -164,6 +164,7 @@ struct virtio_pci_common_cfg {
    __le32 queue_avail_hi;          /* read-write */
    __le32 queue_used_lo;           /* read-write */
    __le32 queue_used_hi;           /* read-write */
+   __le16 queue_notify_data;       /* read-write */
  };

So I had the same concern as previous version.

This breaks uABI where program may try to use sizeof(struct
virtio_pci_common_cfg).

We probably need a container structure here.

I see, I plan to add a struct like this, do you think it's appropriate?

struct virtio_pci_common_cfg_v1 {
        struct virtio_pci_common_cfg cfg;
        __le16 queue_notify_data;       /* read-write */
}

Something like this but we probably need a better name.

how about this?

        /* Ext Fields in VIRTIO_PCI_CAP_COMMON_CFG: */
        struct virtio_pci_common_cfg_ext {
                struct virtio_pci_common_cfg cfg;

                __le16 queue_notify_data;       /* read-write */

                __le16 reserved0;
                __le16 reserved1;
                __le16 reserved2;
                __le16 reserved3;
                __le16 reserved4;
                __le16 reserved5;
                __le16 reserved6;
                __le16 reserved7;
                __le16 reserved8;
                __le16 reserved9;
                __le16 reserved10;
                __le16 reserved11;
                __le16 reserved12;
                __le16 reserved13;
                __le16 reserved14;
        };

I still think the container without padding is better. Otherwise
userspace needs to use offset_of() trick instead of sizeof().

In this case, as virtio_pci_common_cfg_ext adds new members in the future, we
will add more container structures.

In that case, I think virtio_pci_common_cfg_v1 is a good name instead.

Something like "virtio_pci_common_cfg_notify" might be a little bit better.

Although there is only one notify_data in this patch, I plan to look like this
after my patch set:

        struct virtio_pci_common_cfg_v1 {
                struct virtio_pci_common_cfg cfg;

                __le16 queue_notify_data;       /* read-write */
                __le16 queue_reset;       /* read-write */
        }

If we use virtio_pci_common_cfg_notify, then we will get two structures after
this patch set:

        struct virtio_pci_common_cfg_notify {
                struct virtio_pci_common_cfg cfg;

                __le16 queue_notify_data;       /* read-write */
        }

        struct virtio_pci_common_cfg_reset {
                struct virtio_pci_common_cfg_notify cfg;

                __le16 queue_reset;       /* read-write */
        }

Right, this is sub-optimal, and we need padding in cfg_notify
probably. But I couldn't think of a better idea currently, maybe we
can listen from others opinion

But we use something like this for vnet_header extension

struct virtio_net_hdr_v1{
};

struct virtio_net_hdr_v1_hash{
struct virtio_net_hdr_v1;
__le32 XXX;
...
__le16 padding;
};

And it's not hard to imagine there would be another container for
struct virtio_net_hdr_v1_hash in the future if we want to extend vnet
header.

Thanks

Thanks.

quoted

Thanks

quoted

Thanks.

quoted

Thanks

quoted

Thanks

quoted

Thanks

quoted

Thanks.

quoted

THanks

quoted

  /* Fields in VIRTIO_PCI_CAP_PCI_CFG: */