On Wed, 24 May 2023 at 08:38, Christoph Hellwig <hch@xxxxxx> wrote:
>
> Add a helper dealing with handling the syncing of a buffered write fallback
> for direct I/O.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> 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
