On 9:42 20/02, Matthew Wilcox wrote:
> On Thu, Feb 20, 2020 at 09:23:55AM -0600, Goldwyn Rodrigues wrote:
> > In case of a block device error, written parameter in iomap_end()
> > is zero as opposed to the amount of submitted I/O.
> > Filesystems such as btrfs need to account for the I/O in ordered
> > extents, even if it resulted in an error. Having (incomplete)
> > submitted bytes in written gives the filesystem the amount of data
> > which has been submitted before the error occurred, and the
> > filesystem code can choose how to use it.
> >
> > The final returned error for iomap_dio_rw() is set by
> > iomap_dio_complete().
> >
> > Partial writes in direct I/O are considered an error. So,
> > ->iomap_end() using written == 0 as error must be changed
> > to written < length. In this case, ext4 is the only user.
>
> I really had a hard time understanding this. I think what you meant
> was:
>
> Currently, I/Os that complete with an error indicate this by passing
> written == 0 to the iomap_end function. However, btrfs needs to know how
> many bytes were written for its own accounting. Change the convention
> to pass the number of bytes which were actually written, and change the
> only user to check for a short write instead of a zero length write.
Yes, thats right. I was trying to cover base from the previous patch
and made a mess of it all. Thanks..
>
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> > ---
> > fs/ext4/inode.c | 2 +-
> > fs/iomap/direct-io.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index e60aca791d3f..e50e7414351a 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -3475,7 +3475,7 @@ static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
> > * the I/O. Any blocks that may have been allocated in preparation for
> > * the direct I/O will be reused during buffered I/O.
> > */
> > - if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written == 0)
> > + if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written < length)
> > return -ENOTBLK;
> >
> > return 0;
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index 41c1e7c20a1f..01865db1bd09 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -264,7 +264,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> > size_t n;
> > if (dio->error) {
> > iov_iter_revert(dio->submit.iter, copied);
> > - copied = ret = 0;
> > + ret = 0;
> > goto out;
> > }
> >
> > --
> > 2.25.0
> >
--
Goldwyn
