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.

Though zone capacity is per-zone attribute, it remains same for all
zones in most cases. Referring to the NVMe ZNS spec, zone capacity
changes associate to RESET_ZONE op when the variable zone capacity bit
is '1'. It hasn't specifically tell what it is changed to. Current ZNS
emulation doesn't change zone capacity as well.

If the Variable Zone Capacity bit is cleared to ‘0’ in the Zone
Operation Characteristics field in the Zoned
Namespace Command Set specific Identify Namespace data structure, then
this field does not change without a change to the format of the zoned
namespace.

If the Variable Zone Capacity bit is set to ‘1’ in the Zone Operation
Characteristics field in the Zoned
Namespace Command Set specific Identify Namespace data structure, then
the zone capacity may
change upon successful completion of a Zone Management Send command
specifying the Zone Send
Action of Reset Zone.

>
> > +    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)?

It can be dropped. I added this for reducing duplication. Thanks!