linux-kernel - Re: Multidevice f2fs mount after disk rearrangement

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Date:   Sat, 04 Jan 2020 22:52:48 +0100
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     linux-f2fs-devel@...ts.sourceforge.net
Cc:     linux-kernel@...r.kernel.org, Jaegeuk Kim <jaegeuk@...nel.org>,
        Chao Yu <chao@...nel.org>
Subject: Re: Multidevice f2fs mount after disk rearrangement

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.

Am I really supposed to do this manually ;)?

-- 
   Oleksandr Natalenko (post-factum)