Re: [PATCH v2 2/4] qcow2: add configurations for zoned format extension

[Sam Li]

Stefan Hajnoczi <stefanha@redhat.com> 于2023年8月21日周一 21:31写道：
>
> On Mon, Aug 14, 2023 at 04:58:00PM +0800, Sam Li wrote:
> > diff --git a/block/qcow2.h b/block/qcow2.h
> > index f789ce3ae0..3694c8d217 100644
> > --- a/block/qcow2.h
> > +++ b/block/qcow2.h
> > @@ -236,6 +236,20 @@ typedef struct Qcow2CryptoHeaderExtension {
> >      uint64_t length;
> >  } QEMU_PACKED Qcow2CryptoHeaderExtension;
> >
> > +typedef struct Qcow2ZonedHeaderExtension {
> > +    /* Zoned device attributes */
> > +    uint8_t zoned_profile;
> > +    uint8_t zoned;
> > +    uint16_t reserved16;
> > +    uint32_t zone_size;
> > +    uint32_t zone_capacity;
>
> Should zone capacity be stored individually for each zone (alongside the
> write pointer and other per zone metadata) instead of as a global value
> for all zones? My understanding is that NVMe ZNS does not have a global
> value and each zone could have a different zone capacity value.
>
> > +    uint32_t nr_zones;
>
> Is this field necessary since it can be derived from other image
> options: nr_zones = DIV_ROUND_UP(total_length, zone_capacity)?

Yes. The bs->total_sectors in refresh_limits is zero. Keeping a
persistent nr_zones helps assigning right value instead of zero.

The process is roughly like this:
*_qcow2_create: calculate nr_zones and write it to zoned_header
->  *_qcow2_update_header: update nr_zones
    ->  *_qcow2_read_extensions: read nr_zones in zoned_header to
Qcow2State and check if right (valid total size here)
      -> *_refresh_limits(): set bl.nr_zones to zoned_header.nr_zones

Sam