Re: [PATCH v2 1/2] fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path

From: Damien Le Moal
Date: Thu Jun 25 2020 - 22:50:38 EST

On 2020/06/26 2:18, Kanchan Joshi wrote:
> Introduce RWF_ZONE_APPEND flag to represent zone-append. User-space
> sends this with write. Add IOCB_ZONE_APPEND which is set in
> kiocb->ki_flags on receiving RWF_ZONE_APPEND.
> Make direct IO submission path use IOCB_ZONE_APPEND to send bio with
> append op. Direct IO completion returns zone-relative offset, in sector
> unit, to upper layer using kiocb->ki_complete interface.
> Report error if zone-append is requested on regular file or on sync
> kiocb (i.e. one without ki_complete).
>
> Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
> Signed-off-by: SelvaKumar S <selvakuma.s1@xxxxxxxxxxx>
> Signed-off-by: Arnav Dawn <a.dawn@xxxxxxxxxxx>
> Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> Signed-off-by: Javier Gonzalez <javier.gonz@xxxxxxxxxxx>
> ---
> fs/block_dev.c | 28 ++++++++++++++++++++++++----
> include/linux/fs.h | 9 +++++++++
> include/uapi/linux/fs.h | 5 ++++-
> 3 files changed, 37 insertions(+), 5 deletions(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 47860e5..5180268 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -185,6 +185,10 @@ static unsigned int dio_bio_write_op(struct kiocb *iocb)
> /* avoid the need for a I/O completion work item */
> if (iocb->ki_flags & IOCB_DSYNC)
> op |= REQ_FUA;
> +
> + if (iocb->ki_flags & IOCB_ZONE_APPEND)
> + op |= REQ_OP_ZONE_APPEND;

This is wrong. REQ_OP_WRITE is already set in the declaration of "op". How can
this work ?

> +
> return op;
> }
>
> @@ -295,6 +299,14 @@ static int blkdev_iopoll(struct kiocb *kiocb, bool wait)
> return blk_poll(q, READ_ONCE(kiocb->ki_cookie), wait);
> }
>
> +static inline long blkdev_bio_end_io_append(struct bio *bio)
> +{
> + sector_t zone_sectors = blk_queue_zone_sectors(bio->bi_disk->queue);
> +
> + /* calculate zone relative offset for zone append */

The name of the function may be better spelling out zone_append instead of just
append. But see next comment.

> + return bio->bi_iter.bi_sector & (zone_sectors - 1);
> +}
> +
> static void blkdev_bio_end_io(struct bio *bio)
> {
> struct blkdev_dio *dio = bio->bi_private;
> @@ -307,15 +319,19 @@ static void blkdev_bio_end_io(struct bio *bio)
> if (!dio->is_sync) {
> struct kiocb *iocb = dio->iocb;
> ssize_t ret;
> + long res2 = 0;
>
> if (likely(!dio->bio.bi_status)) {
> ret = dio->size;
> iocb->ki_pos += ret;
> +

Blank line not needed.

> + if (iocb->ki_flags & IOCB_ZONE_APPEND)> + res2 = blkdev_bio_end_io_append(bio);

The name blkdev_bio_end_io_append() implies a bio end_io callback function,
which is not the case. What about naming this blkdev_bio_res2() and move the if
inside it ?

> } else {
> ret = blk_status_to_errno(dio->bio.bi_status);

add "res2 = 0;" here and drop the declaration initialization. That will avoid
doing the assignment twice for zone append case.

> }
>
> - dio->iocb->ki_complete(iocb, ret, 0);
> + dio->iocb->ki_complete(iocb, ret, res2);
> if (dio->multi_bio)
> bio_put(&dio->bio);
> } else {
> @@ -382,6 +398,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
> bio->bi_private = dio;
> bio->bi_end_io = blkdev_bio_end_io;
> bio->bi_ioprio = iocb->ki_ioprio;
> + bio->bi_opf = is_read ? REQ_OP_READ : dio_bio_write_op(iocb);

Personally, I would prefer a plain "if () else". Or even better: change
dio_bio_write_op() into dio_bio_op() and just have:

bio->bi_opf = dio_bio_op(iocb);

>
> ret = bio_iov_iter_get_pages(bio, iter);
> if (unlikely(ret)) {
> @@ -391,11 +408,9 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
> }
>
> if (is_read) {
> - bio->bi_opf = REQ_OP_READ;
> if (dio->should_dirty)
> bio_set_pages_dirty(bio);
> } else {
> - bio->bi_opf = dio_bio_write_op(iocb);
> task_io_account_write(bio->bi_iter.bi_size);
> }
>
> @@ -465,12 +480,17 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
> static ssize_t
> blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> {
> + bool is_sync = is_sync_kiocb(iocb);
> int nr_pages;
>
> + /* zone-append is supported only on async-kiocb */
> + if (is_sync && iocb->ki_flags & IOCB_ZONE_APPEND)
> + return -EINVAL;
> +
> nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES + 1);
> if (!nr_pages)
> return 0;
> - if (is_sync_kiocb(iocb) && nr_pages <= BIO_MAX_PAGES)
> + if (is_sync && nr_pages <= BIO_MAX_PAGES)
> return __blkdev_direct_IO_simple(iocb, iter, nr_pages);
>
> return __blkdev_direct_IO(iocb, iter, min(nr_pages, BIO_MAX_PAGES));
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 6c4ab4d..3202d9a 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -315,6 +315,7 @@ enum rw_hint {
> #define IOCB_SYNC (1 << 5)
> #define IOCB_WRITE (1 << 6)
> #define IOCB_NOWAIT (1 << 7)
> +#define IOCB_ZONE_APPEND (1 << 8)
>
> struct kiocb {
> struct file *ki_filp;
> @@ -3456,6 +3457,14 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
> ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
> if (flags & RWF_APPEND)
> ki->ki_flags |= IOCB_APPEND;
> + if (flags & RWF_ZONE_APPEND) {
> + /* currently support block device only */
> + umode_t mode = file_inode(ki->ki_filp)->i_mode;
> +
> + if (!(S_ISBLK(mode)))
> + return -EOPNOTSUPP;
> + ki->ki_flags |= IOCB_ZONE_APPEND;
> + }
> return 0;
> }
>
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 379a612..1ce06e9 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -299,8 +299,11 @@ typedef int __bitwise __kernel_rwf_t;
> /* per-IO O_APPEND */
> #define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
>
> +/* per-IO O_APPEND */
> +#define RWF_ZONE_APPEND ((__force __kernel_rwf_t)0x00000020)
> +
> /* mask of flags supported by the kernel */
> #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
> - RWF_APPEND)
> + RWF_APPEND | RWF_ZONE_APPEND)
>
> #endif /* _UAPI_LINUX_FS_H */
>


--
Damien Le Moal
Western Digital Research