Re: [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Aug 20, 2021 at 05:35:21PM +0800, Chao Yu wrote:
> > > > > 
> > > > > Hmm, I'm still trying to deal with this as a corner case where the writes
> > > > > haven't completed due to an error. How about keeping the preallocated block
> > > > > offsets and releasing them if we get an error? Do we need to handle EIO right?
> > > > 
> > > > What about the case that CP + SPO following DIO preallocation? User will
> > > > encounter uninitialized block after recovery.
> > > 
> > > I think buffered writes as a workaround can expose the last unwritten block as
> > > well, if SPO happens right after block allocation. We may need to compromise
> > > at certain level?
> > > 
> > 
> > Freeing preallocated blocks on error would be better than nothing, although note
> > that the preallocated blocks may have filled an arbitrary sequence of holes --
> > so simply truncating past EOF would *not* be sufficient.
> > 
> > But really filesystems need to be designed to never expose uninitialized data,
> > even if I/O errors or a sudden power failure occurs.  It is unfortunate that
> > f2fs apparently wasn't designed with that goal in mind.
> > 
> > In any case, I don't think we can proceed with any other f2fs direct I/O
> > improvements until this data leakage bug can be solved one way or another.  If
> > my patch to remove support for allocating writes isn't acceptable and the
> > desired solution is going to require some more invasive f2fs surgery, are you or
> > Chao going to work on it?  I'm not sure there's much I can do here.
> 
> I may have time to take look into the implementation as I proposed above, maybe
> just enabling this in FSYNC_MODE_STRICT mode if user concerns unwritten data?
> thoughts?
> 

What does this have to do with fsync?

- Eric


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