Re: [PATCH v2] virtio_blk: add VIRTIO_BLK_F_LIFETIME feature support

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Dec 04, 2022 at 02:00:25PM +0200, Alvaro Karsz wrote:
> > I don't see the connection. virtio would often pass through lifetime
> > info from the host. If other devices gain more info then it will make
> > sense to add that to virtio, too.
> 
> > Depends. If we expect more types, then I think we
> > can solve this by passing an array of values.
> 
> 
> Good idea!
> 
> We could pass something like virtio_blk_lifetime_ioctl struct to userspace:
> 
> enum blk_lifetime_type {
>          VIRTIO_BLK_LIFETIME_PRE_EOL_TYPE_A_B = 1,
> };
> 
> struct virtio_blk_lifetime_element {
>         void *data;
>         enum blk_lifetime_type;
> };
> 
> struct virtio_blk_lifetime_ioctl {
>         struct virtio_blk_lifetime_element elements[];
>         u32 elements_num;
> };
> 
> If just VIRTIO_BLK_F_LIFETIME is negotiated, the array size is 1, and
> the element type is VIRTIO_BLK_LIFETIME_PRE_EOL_TYPE_A_B, so the user
> will know that this is a virtio_blk_lifetime struct.
> This seems general enough to handle future additions and to handle out
> of order types (if for example VIRTIO_BLK_LIFETIME is not negotiated
> and VIRTIO_BLK_LIFETIME_FUTURE is).
> 
> The only downside I can think of is if we add new fields to the struct
> virtio_blk_lifetime struct, instead of creating a new, dedicated
> struct in the spec.
> For example:
> 
> struct virtio_blk_lifetime {
>   le16 pre_eol_info;
>   le16 device_lifetime_est_typ_a;
>   le16 device_lifetime_est_typ_b;
>   le16 device_lifetime_est_typ_c;  //only if
> VIRTIO_BLK_LIFETIME_FUTURE is negotiated
> };
> 
> In this case, we may need to split it into 2 different structs, and
> pass it as 2 elements to userspace.
> 
> What do you think?
> Should I go ahead and create a new version?
> 
> 
> Alvaro

And now is this generic enough to disconnect from virtio and
make it a generic blk thing?

-- 
MST

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