linux-ext4 - Re: [PATCH 1/2] fuse2fs: mount norecovery if main block device is readonly

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Message-ID: <20251017233057.GK6170@frogsfrogsfrogs>
Date: Fri, 17 Oct 2025 16:30:57 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Dave Dykstra <dwd@...n.ch>
Cc: tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] fuse2fs: mount norecovery if main block device is
 readonly

On Fri, Oct 17, 2025 at 03:20:00PM -0500, Dave Dykstra wrote:
> On Fri, Oct 17, 2025 at 12:38:41PM -0700, Darrick J. Wong wrote:
> > On Thu, Oct 16, 2025 at 02:34:18PM -0500, Dave Dykstra wrote:
> ...
> > > > +		err_printf(ff, "%s.\n",
> > > > +			   _("read-only device, trying to mount norecovery"));
> > > > +		flags &= ~EXT2_FLAG_RW;
> > > > +		ff->ro = 1;
> > > > +		ff->norecovery = 1;
> > > 
> > > I don't think it's good to switch to read-only+norecovery even when a
> > > read-write mode was requested.  That goes too far.
> > 
> > The block device cannot be opened for write, so the mount cannot allow
> > user programs to write to files, and the fs driver cannot recover the
> > journal and it cannot write to the disk.  The only other choice would
> > be to fail the mount.
> 
> Yes, I think it's better to fail the mount if recovery is needed and it
> can't be done.
> 
> > norecovery is wrong though.  The kernel fails the mount if the journal
> > needs recovery, the block device is ro, and the user didn't specify
> > norecovery.
> 
> That makes more sense.
> 
> > > It also doesn't catch when recovery is needed.
> > 
> > What specifically do you mean "catch when recovery is needed"?  68 lines
> > down from the ext2fs_open2 call is a check for the needsrecovery state,
> > followed by recovering the journal.
> 
> I meant that it should fail in that case because it can't recover.
> 
> > > My proposed patch only reopens read-only
> > > when ro was requested and then later checks to see if recovery is needed
> > > and if so, errors out.
> > 
> > Your patch also didn't re-check the feature support after reopening the
> > block device, which you dismissed even though that can lead to
> > catastrophic behavior.
> 
> In this version of the patch there is no reopening, there is only a
> switch to open without RW if the RW open fails.  So all feature checks
> happen after it.

Well I'm struggling to reshuffle my patch deck to keep up with you.

I already _had_ patches to fix every thing you've mentioned, but since
you pre-declared you wouldn't make time even to go look at my patch
stack why the hell am I even bothering?

I no longer have patience for these interactions.

--D

> Dave
>