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Subject: Re: [f2fs-dev] Multidevice f2fs mount after disk rearrangement
To:     Oleksandr Natalenko <oleksandr@natalenko.name>,
        <linux-f2fs-devel@lists.sourceforge.net>
CC:     Jaegeuk Kim <jaegeuk@kernel.org>, <linux-kernel@vger.kernel.org>
References: <4c6cf8418236145f7124ac61eb2908ad@natalenko.name>
 <2c4cafd35d1595a62134203669d7c244@natalenko.name>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <e773d576-9458-48d7-bad4-dd4f8c61ebd3@huawei.com>
Date:   Mon, 6 Jan 2020 11:41:04 +0800
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Hello,

Thanks for the report. :)

On 2020/1/5 5:52, Oleksandr Natalenko via Linux-f2fs-devel wrote:
> Hi.
> 
> On 04.01.2020 17:29, Oleksandr Natalenko wrote:
>> I was brave enough to create f2fs filesystem spanning through 2
>> physical device using this command:
>>
>> # mkfs.f2fs -t 0 /dev/sdc -c /dev/sdd
>>
>> It worked fine until I removed /dev/sdb from my system, so f2fs devices 
>> became:
>>
>> /dev/sdc -> /dev/sdb
>> /dev/sdd -> /dev/sdc
>>
>> Now, when I try to mount it, I get the following:
>>
>> # mount -t f2fs /dev/sdb /mnt/fs
>> mount: /mnt/fs: mount(2) system call failed: No such file or directory.
>>
>> In dmesg:
>>
>> [Jan 4 17:25] F2FS-fs (sdb): Mount Device [ 0]:             /dev/sdc,
>>   59063,        0 -  1cd6fff
>> [  +0,000024] F2FS-fs (sdb): Failed to find devices
>>
>> fsck also fails with the following assertion:
>>
>> [ASSERT] (init_sb_info: 908) !strcmp((char *)sb->devs[i].path, (char
>> *)c.devices[i].path)
>>
>> Am I doing something obviously stupid, and the device path can be
>> (somehow) changed so that the mount succeeds, or this is unfixable,
>> and f2fs relies on persistent device naming?
>>
>> Please suggest.
>>
>> Thank you.
> 
> Erm, fine. I studied f2fs-tools code a little bit and discovered that 
> superblock indeed had /dev/sdX paths saved as strings. So I fired up 
> hexedit and just changed the superblock directly on the first device, 
> substituting sdc with sdb and sdd with sdc (I did it twice; I guess 
> there are 2 copies of superblock), and after this the mount worked.

Alright, it works if superblock checksum feature is off...

> 
> Am I really supposed to do this manually ;)?

We'd better add that ability in tune.f2fs. And I guess we need to let
kernel/fsck to notice that case, and give hint to run tune.f2fs to
reconfigure primary/secondary/... device paths.

Thanks,

>