From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-btrfs-owner@vger.kernel.org>
Received: from mail-it0-f47.google.com ([209.85.214.47]:37810 "EHLO
	mail-it0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751171AbcGFSE6 (ORCPT
	<rfc822;linux-btrfs@vger.kernel.org>); Wed, 6 Jul 2016 14:04:58 -0400
Received: by mail-it0-f47.google.com with SMTP id f6so1979875ith.0
        for <linux-btrfs@vger.kernel.org>; Wed, 06 Jul 2016 11:04:57 -0700 (PDT)
Subject: Re: 64-btrfs.rules and degraded boot
To: Chris Murphy <lists@colorremedies.com>,
        Andrei Borzenkov <arvidjaar@gmail.com>
References: <CAJCQCtRQBGNeCyENzTPT=yiqs3Tcc=aD8v6usKNtTnvyOd0uqw@mail.gmail.com>
 <20160705212706.719397fc@jupiter.sol.kaishome.de>
 <CAJCQCtRyvC6J=KJSVYRd1sOWPoVm69tA--3U8kAVdDynkziwNA@mail.gmail.com>
 <CAJCQCtS7OgKKzstJDz52Sd6+SJygDzoVzMhvwHqGxFmihr6Aqg@mail.gmail.com>
 <CAA91j0VbaRpt46tYf_oqd7fRuRn_ev-=Zxf_Bwiwd=TUHR+2Ow@mail.gmail.com>
 <CAJCQCtSZ=7v5PgD4mYKhayg03UfVqCV0ADBSjTsFDHiVcdxAjw@mail.gmail.com>
Cc: Kai Krakow <hurikhan77@gmail.com>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
From: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
Message-ID: <44c18e92-69b4-1409-1bf3-b1d08f6f84db@gmail.com>
Date: Wed, 6 Jul 2016 14:04:50 -0400
MIME-Version: 1.0
In-Reply-To: <CAJCQCtSZ=7v5PgD4mYKhayg03UfVqCV0ADBSjTsFDHiVcdxAjw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Sender: linux-btrfs-owner@vger.kernel.org
List-ID: <linux-btrfs.vger.kernel.org>

On 2016-07-06 13:19, Chris Murphy wrote:
> On Wed, Jul 6, 2016 at 3:51 AM, Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>> 3) can we query btrfs whether it is mountable in degraded mode?
>> according to documentation, "btrfs device ready" (which udev builtin
>> follows) checks "if it has ALL of it’s devices in cache for mounting".
>> This is required for proper systemd ordering of services.
>
> Where does udev builtin use btrfs itself? I see "btrfs ready $device"
> which is not a valid btrfs user space command.
>
> I never get any errors from "btrfs device ready" even when too many
> devices are missing. I don't know what it even does or if it's broken.
>
> This is a three device raid1 where I removed 2 devices and "btrfs
> device ready" does not complain, it always returns silent for me no
> matter what. It's been this way for years as far as I know.
>
> [root@f24s ~]# lvs
>   LV         VG Attr       LSize  Pool       Origin Data%  Meta%  Move
> Log Cpy%Sync Convert
>   1          VG Vwi-a-tz-- 50.00g thintastic        2.55
>   2          VG Vwi-a-tz-- 50.00g thintastic        4.00
>   3          VG Vwi-a-tz-- 50.00g thintastic        2.54
>   thintastic VG twi-aotz-- 90.00g                   5.05   2.92
> [root@f24s ~]# btrfs fi show
> Label: none  uuid: 96240fd9-ea76-47e7-8cf4-05d3570ccfd7
>     Total devices 3 FS bytes used 2.26GiB
>     devid    1 size 50.00GiB used 3.00GiB path /dev/mapper/VG-1
>     devid    2 size 50.00GiB used 2.01GiB path /dev/mapper/VG-2
>     devid    3 size 50.00GiB used 3.01GiB path /dev/mapper/VG-3
>
> [root@f24s ~]# btrfs device ready /dev/mapper/VG-1
> [root@f24s ~]#
> [root@f24s ~]# lvchange -an VG/1
> [root@f24s ~]# lvchange -an VG/2
> [root@f24s ~]# btrfs dev scan
> Scanning for Btrfs filesystems
> [root@f24s ~]# lvs
>   LV         VG Attr       LSize  Pool       Origin Data%  Meta%  Move
> Log Cpy%Sync Convert
>   1          VG Vwi---tz-- 50.00g thintastic
>   2          VG Vwi---tz-- 50.00g thintastic
>   3          VG Vwi-a-tz-- 50.00g thintastic        2.54
>   thintastic VG twi-aotz-- 90.00g                   5.05   2.92
> [root@f24s ~]# btrfs fi show
> warning, device 2 is missing
> Label: none  uuid: 96240fd9-ea76-47e7-8cf4-05d3570ccfd7
>     Total devices 3 FS bytes used 2.26GiB
>     devid    3 size 50.00GiB used 3.01GiB path /dev/mapper/VG-3
>     *** Some devices missing
>
> [root@f24s ~]# btrfs device ready /dev/mapper/VG-3
> [root@f24s ~]#
You won't get any output from it regardless, you have to check the 
return code as it's intended to be a tool for scripts and such.