linux-kernel - Re: WARNING: filesystem loop0 was created with 512 inodes, the real maximum is 511, mounting anyway

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Message-ID: <CAK+_RLmGVr=ngG+Tqum==sDLEeEEz11su92EnoQVG6Zgm2gxzg@mail.gmail.com>
Date:   Mon, 28 Sep 2020 09:23:40 +0100
From:   Tigran Aivazian <aivazian.tigran@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+54b10a5da9e59f1ed979@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING: filesystem loop0 was created with 512 inodes, the real
 maximum is 511, mounting anyway

Hello Dmitry,

On Mon, 28 Sep 2020 at 08:51, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Mon, Sep 28, 2020 at 9:48 AM syzbot
> <syzbot+54b10a5da9e59f1ed979@...kaller.appspotmail.com> wrote:
> > BFS-fs: bfs_fill_super(): WARNING: filesystem loop0 was created with 512 inodes, the real maximum is 511, mounting anyway
>
> This looks like a BFS issue. +BFS maintainers.

No, this is not an issue. In the latest change to BFS I added the
following comment to the header fs/bfs/bfs.h, which explains it:

/* In theory BFS supports up to 512 inodes, numbered from 2 (for /) up
to 513 inclusive.
   In actual fact, attempting to create the 512th inode (i.e. inode
No. 513 or file No. 511)
   will fail with ENOSPC in bfs_add_entry(): the root directory cannot
contain so many entries, counting '..'.
   So, mkfs.bfs(8) should really limit its -N option to 511 and not
512. For now, we just print a warning
   if a filesystem is mounted with such "impossible to fill up" number
of inodes */

Kind regards,
Tigran