linux-ext4 - Re: [BUG REPORT] ext4: “errors=remount-ro” has become “errors=shutdown”?

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Message-ID: <20250103153517.GB1284777@mit.edu>
Date: Fri, 3 Jan 2025 10:35:17 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: Jan Kara <jack@...e.cz>
Cc: Baokun Li <libaokun1@...wei.com>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        Christian Brauner <brauner@...nel.org>, sunyongjian1@...wei.com,
        Yang Erkun <yangerkun@...wei.com>, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: [BUG REPORT] ext4: “errors=remount-ro” has become “errors=shutdown”?

On Fri, Jan 03, 2025 at 11:42:13AM +0100, Jan Kara wrote:
> [CCed XFS and fsdevel list in case people have opinion what would be the
> best interface to know the fs has shutdown]
>  
> > Sorry for the lack of clarity in my previous explanation. The key point
> > is not about removing EXT4_MF_FS_ABORTED, but rather we will set
> > EXT4_FLAGS_SHUTDOWN bit, which not only prevents writes but also prevents
> > reads. Therefore, saying it's not read-only actually means it's completely
> > unreadable.
> 
> Ah, I see. I didn't think about that. Is it that you really want reading to
> work from a filesystem after error? Can you share why (I'm just trying to
> understand the usecase)? Or is this mostly a theoretical usecase?

I don't see how setting the shutdown flag causes reads to fail.  That
was true in an early version of the ext4 patch which implemented
shutdown support, but one of the XFS developers (I don't remember if
it was Dave or Cristoph) objected because XFS did not cause the
read_pages function to fail.  Are you seeing this with an upstream
kernel, or with a patched kernel?  The upstream kernel does *not* have
the check in ext4_readpages() or ext4_read_folio() (post folio
conversion).

					- Ted