On 2021/8/21 2:11, Eric Biggers wrote:
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?
Oops, maybe a separate option is more appropriate.
- Eric
