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

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Message-ID: <20200106183450.GC50058@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Mon, 6 Jan 2020 10:34:50 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <chao@...nel.org>
Subject: Re: Multidevice f2fs mount after disk rearrangement

On 01/04, Oleksandr Natalenko 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.
> 
> Am I really supposed to do this manually ;)?

Thank you for investigating this ahead of me. :) Yes, the device list is stored
in superblock, so hacking it manually should work.

Let me think about a tool to tune that.

Thanks,

> 
> -- 
>   Oleksandr Natalenko (post-factum)