On Thu, Dec 19, 2024 at 05:39:08PM +0000, Christoph Hellwig wrote:
> Add a IOMAP_F_ANON_WRITE flag that indicates that the write I/O does not
> have a target block assigned to it yet at iomap time and the file system
> will do that in the bio submission handler, splitting the I/O as needed.
>
> This is used to implement Zone Append based I/O for zoned XFS, where
> splitting writes to the hardware limits and assigning a zone to them
> happens just before sending the I/O off to the block layer, but could
> also be useful for other things like compressed I/O.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> Documentation/filesystems/iomap/design.rst | 4 ++++
> fs/iomap/buffered-io.c | 13 +++++++++----
> fs/iomap/direct-io.c | 6 ++++--
> include/linux/iomap.h | 7 +++++++
> 4 files changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/filesystems/iomap/design.rst b/Documentation/filesystems/iomap/design.rst
> index b0d0188a095e..28ab3758c474 100644
> --- a/Documentation/filesystems/iomap/design.rst
> +++ b/Documentation/filesystems/iomap/design.rst
> @@ -246,6 +246,10 @@ The fields are as follows:
> * **IOMAP_F_PRIVATE**: Starting with this value, the upper bits can
> be set by the filesystem for its own purposes.
>
> + * **IOMAP_F_ANON_WRITE**: Indicates that (write) I/O does not have a target
> + block assigned to it yet and the file system will do that in the bio
> + submission handler, splitting the I/O as needed.
> +
> These flags can be set by iomap itself during file operations.
> The filesystem should supply an ``->iomap_end`` function if it needs
> to observe these flags:
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 3176dc996fb7..8c18fb2a82e0 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1691,10 +1691,14 @@ static int iomap_submit_ioend(struct iomap_writepage_ctx *wpc, int error)
> * failure happened so that the file system end I/O handler gets called
> * to clean up.
> */
> - if (wpc->ops->submit_ioend)
> + if (wpc->ops->submit_ioend) {
> error = wpc->ops->submit_ioend(wpc, error);
> - else if (!error)
> - submit_bio(&wpc->ioend->io_bio);
> + } else {
> + if (WARN_ON_ONCE(wpc->iomap.flags & IOMAP_F_ANON_WRITE))
> + error = -EIO;
> + if (!error)
> + submit_bio(&wpc->ioend->io_bio);
> + }
>
> if (error) {
> wpc->ioend->io_bio.bi_status = errno_to_blk_status(error);
> @@ -1744,7 +1748,8 @@ static bool iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t pos,
> return false;
> if (pos != wpc->ioend->io_offset + wpc->ioend->io_size)
> return false;
> - if (iomap_sector(&wpc->iomap, pos) !=
> + if (!(wpc->iomap.flags & IOMAP_F_ANON_WRITE) &&
> + iomap_sector(&wpc->iomap, pos) !=
> bio_end_sector(&wpc->ioend->io_bio))
> return false;
> /*
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index b521eb15759e..641649a04614 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -81,10 +81,12 @@ static void iomap_dio_submit_bio(const struct iomap_iter *iter,
> WRITE_ONCE(iocb->private, bio);
> }
>
> - if (dio->dops && dio->dops->submit_io)
> + if (dio->dops && dio->dops->submit_io) {
> dio->dops->submit_io(iter, bio, pos);
> - else
> + } else {
> + WARN_ON_ONCE(iter->iomap.flags & IOMAP_F_ANON_WRITE);
> submit_bio(bio);
Do we need to error the bio instead of submitting it if
IOMAP_F_ANON_WRITE is set here? Or are we relying on the block
layer/device will reject an IO to U64_MAX and produce the EIO for us?
If yes, then that's acceptagble to me
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
--D
> + }
> }
>
> ssize_t iomap_dio_complete(struct iomap_dio *dio)
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 31857d4750a9..36a7298b6cea 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -56,6 +56,10 @@ struct vm_fault;
> *
> * IOMAP_F_BOUNDARY indicates that I/O and I/O completions for this iomap must
> * never be merged with the mapping before it.
> + *
> + * IOMAP_F_ANON_WRITE indicates that (write) I/O does not have a target block
> + * assigned to it yet and the file system will do that in the bio submission
> + * handler, splitting the I/O as needed.
> */
> #define IOMAP_F_NEW (1U << 0)
> #define IOMAP_F_DIRTY (1U << 1)
> @@ -68,6 +72,7 @@ struct vm_fault;
> #endif /* CONFIG_BUFFER_HEAD */
> #define IOMAP_F_XATTR (1U << 5)
> #define IOMAP_F_BOUNDARY (1U << 6)
> +#define IOMAP_F_ANON_WRITE (1U << 7)
>
> /*
> * Flags set by the core iomap code during operations:
> @@ -111,6 +116,8 @@ struct iomap {
>
> static inline sector_t iomap_sector(const struct iomap *iomap, loff_t pos)
> {
> + if (iomap->flags & IOMAP_F_ANON_WRITE)
> + return U64_MAX; /* invalid */
> return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
> }
>
> --
> 2.45.2
>
>
