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Date:   Fri, 28 Aug 2020 09:47:28 +0200
From:   Klaus Jensen <its@irrelevant.dk>
To:     Damien Le Moal <Damien.LeMoal@wdc.com>
Cc:     Niklas Cassel <Niklas.Cassel@wdc.com>,
        Jens Axboe <axboe@kernel.dk>,
        Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] null_blk: add support for max open/active zone limit
 for zoned devices
Message-ID: <20200828074728.GA1343822@apples.localdomain>
References: <20200827135018.63644-1-niklas.cassel@wdc.com>
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On Aug 28 07:36, Damien Le Moal wrote:
> On 2020/08/28 16:23, Klaus Jensen wrote:
> > On Aug 28 07:06, Damien Le Moal wrote:
> >> On 2020/08/27 22:50, Niklas Cassel wrote:
> >>> +static blk_status_t null_finish_zone(struct nullb_device *dev, struc=
t blk_zone *zone)
> >>> +{
> >>> +	if (zone->type =3D=3D BLK_ZONE_TYPE_CONVENTIONAL)
> >>> +		return BLK_STS_IOERR;
> >>> +
> >>> +	switch (zone->cond) {
> >>> +	case BLK_ZONE_COND_FULL:
> >>> +		/* finish operation on full is not an error */
> >>> +		return BLK_STS_OK;
> >>> +	case BLK_ZONE_COND_EMPTY:
> >>> +		if (!null_manage_zone_resources(dev, zone))
> >>
> >> OK. So you are hitting a fuzzy case here that is not actually well des=
cribed in
> >> the standards. That is, does finishing an empty zone necessarilly impl=
y a
> >> temporary transition through imp open ? Which you are assuming is a ye=
s here.
> >> Personally, I would say that is not necessary, but no strong feeling e=
ither way.
> >>
> >=20
> > For ZNS, the spec is pretty clear that ZSE to ZSF is a legal direct
> > transition. So I don't think the transition should be allowed to fail
> > due to a lack of resources.
>=20
> I had a doubt and checked again ZBC & ZAC. I section 4.4.3.2.4 it says:
>=20
> The Zone Condition state machine (see 4.4.3.5) requires the specified zon=
e to
> have a Zone Condition of EXPLICITLY OPENED or IMPLICITLY OPENED before a =
finish
> zone operation is performed. If a zone with a Zone Condition of EMPTY or =
CLOSED
> is specified for a finish zone operation, prior to processing the finish =
zone
> operation, then the Zone Condition state machine requires that:
> a) a manage open zone resources operation (see 4.4.3.2.6) be performed; a=
nd
> b) the Zone Condition becomes IMPLICITLY OPENED.
>=20
> And section 5.3 describing the zone finish command points to this section.
> So this is not the same as ZNS.
>=20
> As Niklas mentioned, nullblk tends to follow more ZBC than ZNS, so the co=
de is
> correct in this respect. We could also lean toward ZNS on this one. I per=
sonally
>  have no strong opinion either way since there is not real good reasons f=
or
> finishing an empty zone that I can think of.
>=20
>=20

Alrighty then; thanks for looking it up! I won't fight for the ZNS
behavior then :)

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