Re: [PATCH 09/11] fs: factor out a direct_write_fallback helper

[Miklos Szeredi <miklos@szeredi.hu>]

On Wed, 24 May 2023 at 08:38, Christoph Hellwig <hch@lst.de> wrote:
>
> Add a helper dealing with handling the syncing of a buffered write fallback
> for direct I/O.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/libfs.c         | 36 +++++++++++++++++++++++++
>  include/linux/fs.h |  2 ++
>  mm/filemap.c       | 66 +++++++++++-----------------------------------
>  3 files changed, 53 insertions(+), 51 deletions(-)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 89cf614a327158..ad37a49e2ecfb7 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -1613,3 +1613,39 @@ u64 inode_query_iversion(struct inode *inode)
>         return cur >> I_VERSION_QUERIED_SHIFT;
>  }
>  EXPORT_SYMBOL(inode_query_iversion);
> +
> +ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
> +               ssize_t direct_written, ssize_t buffered_written)
> +{
> +       struct address_space *mapping = iocb->ki_filp->f_mapping;
> +       loff_t pos = iocb->ki_pos - buffered_written;
> +       loff_t end = iocb->ki_pos - 1;
> +       int err;
> +
> +       /*
> +        * If the buffered write fallback returned an error, we want to return
> +        * the number of bytes which were written by direct I/O, or the error
> +        * code if that was zero.
> +        *
> +        * Note that this differs from normal direct-io semantics, which will
> +        * return -EFOO even if some bytes were written.
> +        */
> +       if (unlikely(buffered_written < 0))
> +               return buffered_written;

Comment/code mismatch.   The comment says:

if (buffered_written < 0)
        return direct_written ?: buffered_written;

> +
> +       /*
> +        * We need to ensure that the page cache pages are written to disk and
> +        * invalidated to preserve the expected O_DIRECT semantics.
> +        */
> +       err = filemap_write_and_wait_range(mapping, pos, end);
> +       if (err < 0) {
> +               /*
> +                * We don't know how much we wrote, so just return the number of
> +                * bytes which were direct-written
> +                */
> +               return err;

Again comment/code mismatch.

Thanks,
Miklos