On 8/29/23 15:27, Sam Li wrote:
> Damien Le Moal <dlem...@kernel.org> 于2023年8月29日周二 14:06写道：
>>
>> On 8/28/23 20:55, Sam Li wrote:
>>>>> + /* close one implicitly open zones to make it available */
>>>>> + for (int i = s->zoned_header.zone_nr_conv;
>>>>> + i < bs->bl.nr_zones; ++i) {
>>>>> + uint64_t *wp = &s->wps->wp[i];
>>>>> + if (qcow2_get_zs(*wp) == BLK_ZS_IOPEN) {
>>>>> + ret = qcow2_write_wp_at(bs, wp, i, BLK_ZS_CLOSED);
>>>>
>>>> I'm wondering if it's correct to store the zone state persistently in
>>>> the qcow2 file. If the guest or QEMU crashes, then zones will be left in
>>>> states like EOPEN. Since the guest software will have forgotten about
>>>> explicitly opened zones, the guest would need to recover zone states.
>>>> I'm not sure if existing software is designed to do that.
>>>>
>>>> Damien: Should the zone state be persistent?
>>
>> Yes and no. Yes you need to preserve/maintain zone states but not as is.
>> With a real drive, if you power cycle the device, you get the following
>> states
>> changes:
>>
>> Before | After power cycle
>> ----------------+-------------------
>> EMPTY | EMPTY
>> FULL | FULL
>> IMP. OPEN | CLOSED
>> EXP. OPEN | CLOSED
>> CLOSED | CLOSED
>> READ=ONLY | READ-ONLY
>> OFFLINE | OFFLINE
>>
>> So any open (implicit or explicit) zone will show up as closed after power
>> cycle. That is, the number of "active" zones does not change.
>> For the qcow2 emulation, as long as you do not also emulate read-only and
>> offline zones, you actually do not need to save the zone state in the zone
>> metadata. On startup, you can infer the state from the zone write pointer:
>>
>> zone wp == zone start -> EMPTY
>> zone wp >= zone capacity -> FULL
>> zone wp > zone start -> CLOSED
>>
>> And make sure that all closed zones are counted as the initial number of
>> active
>> zones. The initial number of open zones will always be 0.
>>
>> So it is easy :)
>
> Thanks for the explanations!
>
> Read-only and offline are device internal events. Does qcow2 emulation
> need to emulate that?
>
> Current NVMe ZNS emulation in QEMU has a nvme_offline_zone() function.
> Does it suggest keeping the offline state persistent?
> https://github.com/qemu/qemu/blob/master/hw/nvme/ctrl.c#L3740
The offline state is useful for testing only. If a zone goes offline, it
generally means that the device is dying...
At least for now, I do not think it is needed for qcow2. That can always be
added later.
>
> Sam
--
Damien Le Moal
Western Digital Research
