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From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     "dsterba@suse.cz" <dsterba@suse.cz>,
        Naohiro Aota <Naohiro.Aota@wdc.com>
CC:     "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
        David Sterba <dsterba@suse.com>, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>, Qu Wenruo <wqu@suse.com>,
        Nikolay Borisov <nborisov@suse.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Hannes Reinecke <hare@suse.com>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        =?iso-8859-1?Q?Matias_Bj=F8rling?= <mb@lightnvm.io>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        Bart Van Assche <bvanassche@acm.org>
Subject: Re: [PATCH v2 00/19] btrfs zoned block device support
Thread-Topic: [PATCH v2 00/19] btrfs zoned block device support
Thread-Index: AQHVHTKAJDlGAC+HkUGU89kQ+2+L3A==
Date:   Mon, 17 Jun 2019 02:44:03 +0000
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David,=0A=
=0A=
On 2019/06/13 22:45, David Sterba wrote:=0A=
> On Thu, Jun 13, 2019 at 04:59:23AM +0000, Naohiro Aota wrote:=0A=
>> On 2019/06/13 2:50, David Sterba wrote:=0A=
>>> On Fri, Jun 07, 2019 at 10:10:06PM +0900, Naohiro Aota wrote:=0A=
>>>> btrfs zoned block device support=0A=
>>>>=0A=
>>>> This series adds zoned block device support to btrfs.=0A=
>>>=0A=
>>> The overall design sounds ok.=0A=
>>>=0A=
>>> I skimmed through the patches and the biggest task I see is how to make=
=0A=
>>> the hmzoned adjustments and branches less visible, ie. there are too=0A=
>>> many if (hmzoned) { do something } standing out. But that's merely a=0A=
>>> matter of wrappers and maybe an abstraction here and there.=0A=
>>=0A=
>> Sure. I'll add some more abstractions in the next version.=0A=
> =0A=
> Ok, I'll reply to the patches with specific things.=0A=
> =0A=
>>> How can I test the zoned devices backed by files (or regular disks)? I=
=0A=
>>> searched for some concrete example eg. for qemu or dm-zoned, but closes=
t=0A=
>>> match was a text description in libzbc README that it's possible to=0A=
>>> implement. All other howtos expect a real zoned device.=0A=
>>=0A=
>> You can use tcmu-runer [1] to create an emulated zoned device backed by =
=0A=
>> a regular file. Here is a setup how-to:=0A=
>> http://zonedstorage.io/projects/tcmu-runner/#compilation-and-installatio=
n=0A=
> =0A=
> That looks great, thanks. I wonder why there's no way to find that, all=
=0A=
> I got were dead links to linux-iscsi.org or tutorials of targetcli that=
=0A=
> were years old and not working.=0A=
=0A=
The site went online 4 days ago :) We will advertise it whenever we can. Th=
is is=0A=
intended to document all things "zoned block device" including Btrfs suppor=
t,=0A=
when we get it finished :)=0A=
=0A=
> =0A=
> Feeding the textual commands to targetcli is not exactly what I'd=0A=
> expect for scripting, but at least it seems to work.=0A=
=0A=
Yes, this is not exactly obvious, but that is how most automation with linu=
x=0A=
iscsi is done.=0A=
=0A=
> =0A=
> I tried to pass an emulated ZBC device on host to KVM guest (as a scsi=0A=
> device) but lsscsi does not recognize that it as a zonde device (just a=
=0A=
> QEMU harddisk). So this seems the emulation must be done inside the VM.=
=0A=
> =0A=
=0A=
What driver did you use for the drive ? virtio block ? I have not touch tha=
t=0A=
driver nor qemu side, so zoned block dev support is likely missing. I will =
add=0A=
it. That would be especially useful for testing with a real drive. In the c=
ase=0A=
of tcmu runner, the initiator can be started in the guest directly and the=
=0A=
target emulation done either in the guest if loopback is used, or on the ho=
st=0A=
using iscsi connection. The former is what we use all the time and so is we=
ll=0A=
tested. I have to admit that testing with iscsi is lacking... Will add that=
 to=0A=
the todo list.=0A=
=0A=
Best regards.=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=