On Thu, Jan 21, 2021 at 09:59:05AM +0100, Christoph Hellwig wrote:
> Add a flag to signal an only pure overwrites are allowed.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
Agreed that the explicit flag name is much more clear:
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> fs/iomap/direct-io.c | 7 +++++++
> include/linux/iomap.h | 8 ++++++++
> 2 files changed, 15 insertions(+)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 947343730e2c93..65d32364345d22 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -485,6 +485,13 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> iomap_flags |= IOMAP_NOWAIT;
> }
>
> + if (dio_flags & IOMAP_DIO_OVERWRITE_ONLY) {
> + ret = -EAGAIN;
> + if (pos >= dio->i_size || pos + count > dio->i_size)
> + goto out_free_dio;
> + iomap_flags |= IOMAP_OVERWRITE_ONLY;
> + }
> +
> ret = filemap_write_and_wait_range(mapping, pos, end);
> if (ret)
> goto out_free_dio;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index be4e1e1e01e801..cfa20afd7d5b87 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -122,6 +122,7 @@ struct iomap_page_ops {
> #define IOMAP_FAULT (1 << 3) /* mapping for page fault */
> #define IOMAP_DIRECT (1 << 4) /* direct I/O */
> #define IOMAP_NOWAIT (1 << 5) /* do not block */
> +#define IOMAP_OVERWRITE_ONLY (1 << 6) /* purely overwrites allowed */
>
> struct iomap_ops {
> /*
> @@ -262,6 +263,13 @@ struct iomap_dio_ops {
> */
> #define IOMAP_DIO_FORCE_WAIT (1 << 0)
>
> +/*
> + * Do not allocate blocks or zero partial blocks, but instead fall back to
> + * the caller by returning -EAGAIN. Used to optimize direct I/O writes that
> + * are not aligned to the file system block size.
> + */
> +#define IOMAP_DIO_OVERWRITE_ONLY (1 << 1)
> +
> ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
> unsigned int dio_flags);
> --
> 2.29.2
>
