On Wed, Dec 11, 2024 at 09:53:44AM +0100, Christoph Hellwig wrote:
> Provide helpers for file systems to split bios in the direct I/O and
> writeback I/O submission handlers.
>
> This Follows btrfs' lead and don't try to build bios to hardware limits
> for zone append commands, but instead build them as normal unconstrained
> bios and split them to the hardware limits in the I/O submission handler.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/iomap/Makefile | 1 +
> fs/iomap/buffered-io.c | 43 ++++++++++++++-----------
> fs/iomap/ioend.c | 73 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/iomap.h | 9 ++++++
> 4 files changed, 108 insertions(+), 18 deletions(-)
> create mode 100644 fs/iomap/ioend.c
>
...
> diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
> new file mode 100644
> index 000000000000..f3d98121c593
> --- /dev/null
> +++ b/fs/iomap/ioend.c
...
It might be useful to add a small comment here to point out this splits
from the front of the ioend (i.e. akin to bio_split()), documents the
params, and maybe mentions the ioend relationship requirements (i.e.
according to bio_split(), the split ioend bio refers to the vectors in
the original ioend bio).
Brian
> +struct iomap_ioend *iomap_split_ioend(struct iomap_ioend *ioend, bool is_append,
> + unsigned int *alloc_len)
> +{
> + struct bio *bio = &ioend->io_bio;
> + struct iomap_ioend *split_ioend;
> + struct bio *split;
> + int sector_offset;
> + unsigned int nr_segs;
> +
> + if (is_append) {
> + struct queue_limits *lim = bdev_limits(bio->bi_bdev);
> +
> + sector_offset = bio_split_rw_at(bio, lim, &nr_segs,
> + min(lim->max_zone_append_sectors << SECTOR_SHIFT,
> + *alloc_len));
> + if (!sector_offset)
> + return NULL;
> + } else {
> + if (bio->bi_iter.bi_size <= *alloc_len)
> + return NULL;
> + sector_offset = *alloc_len >> SECTOR_SHIFT;
> + }
> +
> + /* ensure the split ioend is still block size aligned */
> + sector_offset = ALIGN_DOWN(sector_offset << SECTOR_SHIFT,
> + i_blocksize(ioend->io_inode)) >> SECTOR_SHIFT;
> +
> + split = bio_split(bio, sector_offset, GFP_NOFS, &iomap_ioend_bioset);
> + if (!split)
> + return NULL;
> + split->bi_private = bio->bi_private;
> + split->bi_end_io = bio->bi_end_io;
> +
> + split_ioend = iomap_init_ioend(ioend->io_inode, split, ioend->io_offset,
> + ioend->io_flags);
> + split_ioend->io_parent = ioend;
> +
> + atomic_inc(&ioend->io_remaining);
> + ioend->io_offset += split_ioend->io_size;
> + ioend->io_size -= split_ioend->io_size;
> +
> + split_ioend->io_sector = ioend->io_sector;
> + if (!is_append)
> + ioend->io_sector += (split_ioend->io_size >> SECTOR_SHIFT);
> +
> + *alloc_len -= split->bi_iter.bi_size;
> + return split_ioend;
> +}
> +EXPORT_SYMBOL_GPL(iomap_split_ioend);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 173d490c20ba..eaa8cb9083eb 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -354,6 +354,9 @@ struct iomap_ioend {
> struct list_head io_list; /* next ioend in chain */
> u16 io_flags; /* IOMAP_IOEND_* */
> struct inode *io_inode; /* file being written to */
> + atomic_t io_remaining; /* completetion defer count */
> + int io_error; /* stashed away status */
> + struct iomap_ioend *io_parent; /* parent for completions */
> size_t io_size; /* size of the extent */
> loff_t io_offset; /* offset in the file */
> sector_t io_sector; /* start sector of ioend */
> @@ -404,6 +407,10 @@ struct iomap_writepage_ctx {
> u32 nr_folios; /* folios added to the ioend */
> };
>
> +struct iomap_ioend *iomap_init_ioend(struct inode *inode, struct bio *bio,
> + loff_t file_offset, u16 flags);
> +struct iomap_ioend *iomap_split_ioend(struct iomap_ioend *ioend, bool is_append,
> + unsigned int *alloc_len);
> void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
> void iomap_ioend_try_merge(struct iomap_ioend *ioend,
> struct list_head *more_ioends);
> @@ -475,4 +482,6 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
> # define iomap_swapfile_activate(sis, swapfile, pagespan, ops) (-EIO)
> #endif /* CONFIG_SWAP */
>
> +extern struct bio_set iomap_ioend_bioset;
> +
> #endif /* LINUX_IOMAP_H */
> --
> 2.45.2
>
>
