[PATCH v2 0/2] zone-append support in io-uring and aio

[PATCH v2 0/2] zone-append support in io-uring and aio

[Kanchan Joshi]

[Revised as per feedback from Damien, Pavel, Jens, Christoph, Matias, Wilcox]

This patchset enables zone-append using io-uring/linux-aio, on block IO path.
Purpose is to provide zone-append consumption ability to applications which are
using zoned-block-device directly.

The application may specify RWF_ZONE_APPEND flag with write when it wants to
send zone-append. RWF_* flags work with a certain subset of APIs e.g. uring,
aio, and pwritev2. An error is reported if zone-append is requested using
pwritev2. It is not in the scope of this patchset to support pwritev2 or any
other sync write API for reasons described later.

Zone-append completion result --->
With zone-append, where write took place can only be known after completion.
So apart from usual return value of write, additional mean is needed to obtain
the actual written location.

In aio, this is returned to application using res2 field of io_event -

struct io_event {
        __u64           data;           /* the data field from the iocb */
        __u64           obj;            /* what iocb this event came from */
        __s64           res;            /* result code for this event */
        __s64           res2;           /* secondary result */
};

In io-uring, cqe->flags is repurposed for zone-append result.

struct io_uring_cqe {
        __u64   user_data;      /* sqe->data submission passed back */
        __s32   res;            /* result code for this event */
        __u32   flags;
};

Since 32 bit flags is not sufficient, we choose to return zone-relative offset
in sector/512b units. This can cover zone-size represented by chunk_sectors.
Applications will have the trouble to combine this with zone start to know
disk-relative offset. But if more bits are obtained by pulling from res field
that too would compel application to interpret res field differently, and it
seems more painstaking than the former option.
To keep uniformity, even with aio, zone-relative offset is returned.

Append using io_uring fixed-buffer --->
This is flagged as not-supported at the moment. Reason being, for fixed-buffer
io-uring sends iov_iter of bvec type. But current append-infra in block-layer
does not support such iov_iter.

Block IO vs File IO --->
For now, the user zone-append interface is supported only for zoned-block-device.
Regular files/block-devices are not supported. Regular file-system (e.g. F2FS)
will not need this anyway, because zone peculiarities are abstracted within FS.
At this point, ZoneFS also likes to use append implicitly rather than explicitly.
But if/when ZoneFS starts supporting explicit/on-demand zone-append, the check
allowing-only-block-device should be changed.

Semantics --->
Zone-append, by its nature, may perform write on a different location than what
was specified. It does not fit into POSIX, and trying to fit may just undermine
its benefit. It may be better to keep semantics as close to zone-append as
possible i.e. specify zone-start location, and obtain the actual-write location
post completion. Towards that goal, existing async APIs seem to fit fine.
Async APIs (uring, linux aio) do not work on implicit write-pointer and demand
explicit write offset (which is what we need for append). Neither write-pointer
is taken as input, nor it is updated on completion. And there is a clear way to
get zone-append result. Zone-aware applications while using these async APIs
can be fine with, for the lack of better word, zone-append semantics itself.

Sync APIs work with implicit write-pointer (at least few of those), and there is
no way to obtain zone-append result, making it hard for user-space zone-append.

Tests --->
Using new interface in fio (uring and libaio engine) by extending zbd tests
for zone-append: https://github.com/axboe/fio/pull/1026

Changes since v1:
- No new opcodes in uring or aio. Use RWF_ZONE_APPEND flag instead.
- linux-aio changes vanish because of no new opcode
- Fixed the overflow and other issues mentioned by Damien
- Simplified uring support code, fixed the issues mentioned by Pavel
- Added error checks

Kanchan Joshi (1):
  fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path

Selvakumar S (1):
  io_uring: add support for zone-append

 fs/block_dev.c          | 28 ++++++++++++++++++++++++----
 fs/io_uring.c           | 32 ++++++++++++++++++++++++++++++--
 include/linux/fs.h      |  9 +++++++++
 include/uapi/linux/fs.h |  5 ++++-
 4 files changed, 67 insertions(+), 7 deletions(-)

-- 
2.7.4

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

[Kanchan Joshi]

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@samsung.com>
Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
---
 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;
+
 	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 */
+	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;
+
+				if (iocb->ki_flags & IOCB_ZONE_APPEND)
+					res2 = blkdev_bio_end_io_append(bio);
 			} else {
 				ret = blk_status_to_errno(dio->bio.bi_status);
 			}
 
-			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);
 
 		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 */
-- 
2.7.4

[PATCH v2 2/2] io_uring: add support for zone-append

[Kanchan Joshi]

From: Selvakumar S <selvakuma.s1@samsung.com>

For zone-append, block-layer will return zone-relative offset via ret2
of ki_complete interface. Make changes to collect it, and send to
user-space using ceq->flags.
Detect and report early error if zone-append is requested with
fixed-buffers.

Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
---
 fs/io_uring.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 155f3d8..31a9da58 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -402,6 +402,8 @@ struct io_rw {
 	struct kiocb			kiocb;
 	u64				addr;
 	u64				len;
+	/* zone-relative offset for append, in sectors */
+	u32			append_offset;
 };
 
 struct io_connect {
@@ -541,6 +543,7 @@ enum {
 	REQ_F_NO_FILE_TABLE_BIT,
 	REQ_F_QUEUE_TIMEOUT_BIT,
 	REQ_F_WORK_INITIALIZED_BIT,
+	REQ_F_ZONE_APPEND_BIT,
 
 	/* not a real bit, just to check we're not overflowing the space */
 	__REQ_F_LAST_BIT,
@@ -598,6 +601,8 @@ enum {
 	REQ_F_QUEUE_TIMEOUT	= BIT(REQ_F_QUEUE_TIMEOUT_BIT),
 	/* io_wq_work is initialized */
 	REQ_F_WORK_INITIALIZED	= BIT(REQ_F_WORK_INITIALIZED_BIT),
+	/* to return zone relative offset for zone append*/
+	REQ_F_ZONE_APPEND	= BIT(REQ_F_ZONE_APPEND_BIT),
 };
 
 struct async_poll {
@@ -1745,6 +1750,8 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 
 		if (req->flags & REQ_F_BUFFER_SELECTED)
 			cflags = io_put_kbuf(req);
+		if (req->flags & REQ_F_ZONE_APPEND)
+			cflags = req->rw.append_offset;
 
 		__io_cqring_fill_event(req, req->result, cflags);
 		(*nr_events)++;
@@ -1943,7 +1950,7 @@ static inline void req_set_fail_links(struct io_kiocb *req)
 		req->flags |= REQ_F_FAIL_LINK;
 }
 
-static void io_complete_rw_common(struct kiocb *kiocb, long res)
+static void io_complete_rw_common(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
 	int cflags = 0;
@@ -1953,8 +1960,14 @@ static void io_complete_rw_common(struct kiocb *kiocb, long res)
 
 	if (res != req->result)
 		req_set_fail_links(req);
+
 	if (req->flags & REQ_F_BUFFER_SELECTED)
 		cflags = io_put_kbuf(req);
+
+	/* use cflags to return zone append completion result */
+	if (req->flags & REQ_F_ZONE_APPEND)
+		cflags = res2;
+
 	__io_cqring_add_event(req, res, cflags);
 }
 
@@ -1962,7 +1975,7 @@ static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
 
-	io_complete_rw_common(kiocb, res);
+	io_complete_rw_common(kiocb, res, res2);
 	io_put_req(req);
 }
 
@@ -1975,6 +1988,9 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
 
 	if (res != req->result)
 		req_set_fail_links(req);
+	if (req->flags & REQ_F_ZONE_APPEND)
+		req->rw.append_offset = res2;
+
 	req->result = res;
 	if (res != -EAGAIN)
 		WRITE_ONCE(req->iopoll_completed, 1);
@@ -2127,6 +2143,9 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (kiocb->ki_flags & IOCB_NOWAIT)
 		req->flags |= REQ_F_NOWAIT;
 
+	if (kiocb->ki_flags & IOCB_ZONE_APPEND)
+		req->flags |= REQ_F_ZONE_APPEND;
+
 	if (force_nonblock)
 		kiocb->ki_flags |= IOCB_NOWAIT;
 
@@ -2409,6 +2428,14 @@ static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
 
 	opcode = req->opcode;
 	if (opcode == IORING_OP_READ_FIXED || opcode == IORING_OP_WRITE_FIXED) {
+		/*
+		 * fixed-buffers not supported for zone-append.
+		 * This check can be removed when block-layer starts
+		 * supporting append with iov_iter of bvec type
+		 */
+		if (req->flags == REQ_F_ZONE_APPEND)
+			return -EINVAL;
+
 		*iovec = NULL;
 		return io_import_fixed(req, rw, iter);
 	}
@@ -2704,6 +2731,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock)
 		req->rw.kiocb.ki_flags &= ~IOCB_NOWAIT;
 
 	req->result = 0;
+
 	io_size = ret;
 	if (req->flags & REQ_F_LINK_HEAD)
 		req->result = io_size;
-- 
2.7.4

Re: [PATCH v2 2/2] io_uring: add support for zone-append

[Pavel Begunkov]

On 25/06/2020 20:15, Kanchan Joshi wrote:
> From: Selvakumar S <selvakuma.s1@samsung.com>
> 
> For zone-append, block-layer will return zone-relative offset via ret2
> of ki_complete interface. Make changes to collect it, and send to
> user-space using ceq->flags.
> Detect and report early error if zone-append is requested with
> fixed-buffers.
> 
> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
> ---
>  fs/io_uring.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 155f3d8..31a9da58 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -402,6 +402,8 @@ struct io_rw {
>  	struct kiocb			kiocb;
>  	u64				addr;
>  	u64				len;
> +	/* zone-relative offset for append, in sectors */
> +	u32			append_offset;
>  };
>  
>  struct io_connect {
> @@ -541,6 +543,7 @@ enum {
>  	REQ_F_NO_FILE_TABLE_BIT,
>  	REQ_F_QUEUE_TIMEOUT_BIT,
>  	REQ_F_WORK_INITIALIZED_BIT,
> +	REQ_F_ZONE_APPEND_BIT,
>  
>  	/* not a real bit, just to check we're not overflowing the space */
>  	__REQ_F_LAST_BIT,
> @@ -598,6 +601,8 @@ enum {
>  	REQ_F_QUEUE_TIMEOUT	= BIT(REQ_F_QUEUE_TIMEOUT_BIT),
>  	/* io_wq_work is initialized */
>  	REQ_F_WORK_INITIALIZED	= BIT(REQ_F_WORK_INITIALIZED_BIT),
> +	/* to return zone relative offset for zone append*/
> +	REQ_F_ZONE_APPEND	= BIT(REQ_F_ZONE_APPEND_BIT),

Do we need a new flag? We can check for IOCB_ZONE_APPEND, flags are always
close by in req->rw.kiocb.ki_flags. May require to be careful about not
setting it for read, so not screwing buf select.

>  };
>  
>  struct async_poll {
> @@ -1745,6 +1750,8 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
>  
>  		if (req->flags & REQ_F_BUFFER_SELECTED)
>  			cflags = io_put_kbuf(req);
> +		if (req->flags & REQ_F_ZONE_APPEND)
> +			cflags = req->rw.append_offset;
>  
>  		__io_cqring_fill_event(req, req->result, cflags);
>  		(*nr_events)++;
> @@ -1943,7 +1950,7 @@ static inline void req_set_fail_links(struct io_kiocb *req)
>  		req->flags |= REQ_F_FAIL_LINK;
>  }
>  
> -static void io_complete_rw_common(struct kiocb *kiocb, long res)
> +static void io_complete_rw_common(struct kiocb *kiocb, long res, long res2)
>  {
>  	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
>  	int cflags = 0;
> @@ -1953,8 +1960,14 @@ static void io_complete_rw_common(struct kiocb *kiocb, long res)
>  
>  	if (res != req->result)
>  		req_set_fail_links(req);
> +
>  	if (req->flags & REQ_F_BUFFER_SELECTED)
>  		cflags = io_put_kbuf(req);
> +
> +	/* use cflags to return zone append completion result */
> +	if (req->flags & REQ_F_ZONE_APPEND)
> +		cflags = res2;
> +
>  	__io_cqring_add_event(req, res, cflags);
>  }
>  
> @@ -1962,7 +1975,7 @@ static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
>  {
>  	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
>  
> -	io_complete_rw_common(kiocb, res);
> +	io_complete_rw_common(kiocb, res, res2);
>  	io_put_req(req);
>  }
>  
> @@ -1975,6 +1988,9 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
>  
>  	if (res != req->result)
>  		req_set_fail_links(req);
> +	if (req->flags & REQ_F_ZONE_APPEND)
> +		req->rw.append_offset = res2;
> +
>  	req->result = res;
>  	if (res != -EAGAIN)
>  		WRITE_ONCE(req->iopoll_completed, 1);
> @@ -2127,6 +2143,9 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
>  	if (kiocb->ki_flags & IOCB_NOWAIT)
>  		req->flags |= REQ_F_NOWAIT;
>  
> +	if (kiocb->ki_flags & IOCB_ZONE_APPEND)
> +		req->flags |= REQ_F_ZONE_APPEND;
> +
>  	if (force_nonblock)
>  		kiocb->ki_flags |= IOCB_NOWAIT;
>  
> @@ -2409,6 +2428,14 @@ static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
>  
>  	opcode = req->opcode;
>  	if (opcode == IORING_OP_READ_FIXED || opcode == IORING_OP_WRITE_FIXED) {
> +		/*
> +		 * fixed-buffers not supported for zone-append.
> +		 * This check can be removed when block-layer starts
> +		 * supporting append with iov_iter of bvec type
> +		 */
> +		if (req->flags == REQ_F_ZONE_APPEND)

s/==/&/

> +			return -EINVAL;
> +
>  		*iovec = NULL;
>  		return io_import_fixed(req, rw, iter);
>  	}
> @@ -2704,6 +2731,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock)
>  		req->rw.kiocb.ki_flags &= ~IOCB_NOWAIT;
>  
>  	req->result = 0;
> +

Extra \n

>  	io_size = ret;
>  	if (req->flags & REQ_F_LINK_HEAD)
>  		req->result = io_size;
> 

-- 
Pavel Begunkov

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

[Damien Le Moal]

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@samsung.com>
> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
> ---
>  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

Re: [PATCH v2 0/2] zone-append support in io-uring and aio

[Damien Le Moal]

On 2020/06/26 2:18, Kanchan Joshi wrote:
> [Revised as per feedback from Damien, Pavel, Jens, Christoph, Matias, Wilcox]
> 
> This patchset enables zone-append using io-uring/linux-aio, on block IO path.
> Purpose is to provide zone-append consumption ability to applications which are
> using zoned-block-device directly.
> 
> The application may specify RWF_ZONE_APPEND flag with write when it wants to
> send zone-append. RWF_* flags work with a certain subset of APIs e.g. uring,
> aio, and pwritev2. An error is reported if zone-append is requested using
> pwritev2. It is not in the scope of this patchset to support pwritev2 or any
> other sync write API for reasons described later.
> 
> Zone-append completion result --->
> With zone-append, where write took place can only be known after completion.
> So apart from usual return value of write, additional mean is needed to obtain
> the actual written location.
> 
> In aio, this is returned to application using res2 field of io_event -
> 
> struct io_event {
>         __u64           data;           /* the data field from the iocb */
>         __u64           obj;            /* what iocb this event came from */
>         __s64           res;            /* result code for this event */
>         __s64           res2;           /* secondary result */
> };
> 
> In io-uring, cqe->flags is repurposed for zone-append result.
> 
> struct io_uring_cqe {
>         __u64   user_data;      /* sqe->data submission passed back */
>         __s32   res;            /* result code for this event */
>         __u32   flags;
> };
> 
> Since 32 bit flags is not sufficient, we choose to return zone-relative offset
> in sector/512b units. This can cover zone-size represented by chunk_sectors.
> Applications will have the trouble to combine this with zone start to know
> disk-relative offset. But if more bits are obtained by pulling from res field
> that too would compel application to interpret res field differently, and it
> seems more painstaking than the former option.
> To keep uniformity, even with aio, zone-relative offset is returned.

I am really not a fan of this, to say the least. The input is byte offset, the
output is 512B relative sector count... Arg... We really cannot do better than
that ?

At the very least, byte relative offset ? The main reason is that this is
_somewhat_ acceptable for raw block device accesses since the "sector"
abstraction has a clear meaning, but once we add iomap/zonefs async zone append
support, we really will want to have byte unit as the interface is regular
files, not block device file. We could argue that 512B sector unit is still
around even for files (e.g. block counts in file stat). Bu the different unit
for input and output of one operation is really ugly. This is not nice for the user.

> 
> Append using io_uring fixed-buffer --->
> This is flagged as not-supported at the moment. Reason being, for fixed-buffer
> io-uring sends iov_iter of bvec type. But current append-infra in block-layer
> does not support such iov_iter.
> 
> Block IO vs File IO --->
> For now, the user zone-append interface is supported only for zoned-block-device.
> Regular files/block-devices are not supported. Regular file-system (e.g. F2FS)
> will not need this anyway, because zone peculiarities are abstracted within FS.
> At this point, ZoneFS also likes to use append implicitly rather than explicitly.
> But if/when ZoneFS starts supporting explicit/on-demand zone-append, the check
> allowing-only-block-device should be changed.

Sure, but I think the interface is still a problem. I am not super happy about
the 512B sector unit. Zonefs will be the only file system that will be impacted
since other normal POSIX file system will not have zone append interface for
users. So this is a limited problem. Still, even for raw block device files
accesses, POSIX system calls use Byte unit everywhere. Let's try to use that.

For aio, it is easy since res2 is unsigned long long. For io_uring, as discussed
already, we can still 8 bits from the cqe res. All  you need is to add a small
helper function in userspace iouring.h to simplify the work of the application
to get that result.

> 
> Semantics --->
> Zone-append, by its nature, may perform write on a different location than what
> was specified. It does not fit into POSIX, and trying to fit may just undermine
> its benefit. It may be better to keep semantics as close to zone-append as
> possible i.e. specify zone-start location, and obtain the actual-write location
> post completion. Towards that goal, existing async APIs seem to fit fine.
> Async APIs (uring, linux aio) do not work on implicit write-pointer and demand
> explicit write offset (which is what we need for append). Neither write-pointer

What do you mean by "implicit write pointer" ? Are you referring to the behavior
of AIO write with a block device file open with O_APPEND ? The yes, it does not
work. But that is perfectly fine for regular files, that is for zonefs.

I would prefer that this paragraph simply state the semantic that is implemented
first. Then explain why the choice. But first, clarify how the API works, what
is allowed, what's not etc. That will also simplify reviewing the code as one
can then check the code against the goal.

> is taken as input, nor it is updated on completion. And there is a clear way to
> get zone-append result. Zone-aware applications while using these async APIs
> can be fine with, for the lack of better word, zone-append semantics itself.
> 
> Sync APIs work with implicit write-pointer (at least few of those), and there is
> no way to obtain zone-append result, making it hard for user-space zone-append.

Sync API are executed under inode lock, at least for regular files. So there is
absolutely no problem to use zone append. zonefs does it already. The problem is
the lack of locking for block device file.

> 
> Tests --->
> Using new interface in fio (uring and libaio engine) by extending zbd tests
> for zone-append: https://github.com/axboe/fio/pull/1026
> 
> Changes since v1:
> - No new opcodes in uring or aio. Use RWF_ZONE_APPEND flag instead.
> - linux-aio changes vanish because of no new opcode
> - Fixed the overflow and other issues mentioned by Damien
> - Simplified uring support code, fixed the issues mentioned by Pavel
> - Added error checks
> 
> Kanchan Joshi (1):
>   fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path
> 
> Selvakumar S (1):
>   io_uring: add support for zone-append
> 
>  fs/block_dev.c          | 28 ++++++++++++++++++++++++----
>  fs/io_uring.c           | 32 ++++++++++++++++++++++++++++++--
>  include/linux/fs.h      |  9 +++++++++
>  include/uapi/linux/fs.h |  5 ++++-
>  4 files changed, 67 insertions(+), 7 deletions(-)
> 


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH v2 0/2] zone-append support in io-uring and aio

[javier.gonz]

[-- Attachment #1: Type: text/plain, Size: 4719 bytes --]

On 26.06.2020 03:11, Damien Le Moal wrote:
>On 2020/06/26 2:18, Kanchan Joshi wrote:
>> [Revised as per feedback from Damien, Pavel, Jens, Christoph, Matias, Wilcox]
>>
>> This patchset enables zone-append using io-uring/linux-aio, on block IO path.
>> Purpose is to provide zone-append consumption ability to applications which are
>> using zoned-block-device directly.
>>
>> The application may specify RWF_ZONE_APPEND flag with write when it wants to
>> send zone-append. RWF_* flags work with a certain subset of APIs e.g. uring,
>> aio, and pwritev2. An error is reported if zone-append is requested using
>> pwritev2. It is not in the scope of this patchset to support pwritev2 or any
>> other sync write API for reasons described later.
>>
>> Zone-append completion result --->
>> With zone-append, where write took place can only be known after completion.
>> So apart from usual return value of write, additional mean is needed to obtain
>> the actual written location.
>>
>> In aio, this is returned to application using res2 field of io_event -
>>
>> struct io_event {
>>         __u64           data;           /* the data field from the iocb */
>>         __u64           obj;            /* what iocb this event came from */
>>         __s64           res;            /* result code for this event */
>>         __s64           res2;           /* secondary result */
>> };
>>
>> In io-uring, cqe->flags is repurposed for zone-append result.
>>
>> struct io_uring_cqe {
>>         __u64   user_data;      /* sqe->data submission passed back */
>>         __s32   res;            /* result code for this event */
>>         __u32   flags;
>> };
>>
>> Since 32 bit flags is not sufficient, we choose to return zone-relative offset
>> in sector/512b units. This can cover zone-size represented by chunk_sectors.
>> Applications will have the trouble to combine this with zone start to know
>> disk-relative offset. But if more bits are obtained by pulling from res field
>> that too would compel application to interpret res field differently, and it
>> seems more painstaking than the former option.
>> To keep uniformity, even with aio, zone-relative offset is returned.
>
>I am really not a fan of this, to say the least. The input is byte offset, the
>output is 512B relative sector count... Arg... We really cannot do better than
>that ?
>
>At the very least, byte relative offset ? The main reason is that this is
>_somewhat_ acceptable for raw block device accesses since the "sector"
>abstraction has a clear meaning, but once we add iomap/zonefs async zone append
>support, we really will want to have byte unit as the interface is regular
>files, not block device file. We could argue that 512B sector unit is still
>around even for files (e.g. block counts in file stat). Bu the different unit
>for input and output of one operation is really ugly. This is not nice for the user.
>

You can refer to the discussion with Jens, Pavel and Alex on the uring
interface. With the bits we have and considering the maximun zone size
supported, there is no space for a byte relative offset. We can take
some bits from cqe->res, but we were afraid this is not very
future-proof. Do you have a better idea?


>>
>> Append using io_uring fixed-buffer --->
>> This is flagged as not-supported at the moment. Reason being, for fixed-buffer
>> io-uring sends iov_iter of bvec type. But current append-infra in block-layer
>> does not support such iov_iter.
>>
>> Block IO vs File IO --->
>> For now, the user zone-append interface is supported only for zoned-block-device.
>> Regular files/block-devices are not supported. Regular file-system (e.g. F2FS)
>> will not need this anyway, because zone peculiarities are abstracted within FS.
>> At this point, ZoneFS also likes to use append implicitly rather than explicitly.
>> But if/when ZoneFS starts supporting explicit/on-demand zone-append, the check
>> allowing-only-block-device should be changed.
>
>Sure, but I think the interface is still a problem. I am not super happy about
>the 512B sector unit. Zonefs will be the only file system that will be impacted
>since other normal POSIX file system will not have zone append interface for
>users. So this is a limited problem. Still, even for raw block device files
>accesses, POSIX system calls use Byte unit everywhere. Let's try to use that.
>
>For aio, it is easy since res2 is unsigned long long. For io_uring, as discussed
>already, we can still 8 bits from the cqe res. All  you need is to add a small
>helper function in userspace iouring.h to simplify the work of the application
>to get that result.

Ok. See above. We can do this.

Jens: Do you see this as a problem in the future?

[...]

Javier

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]

Re: [PATCH v2 0/2] zone-append support in io-uring and aio

[Damien Le Moal]

On 2020/06/26 15:37, javier.gonz@samsung.com wrote:
> On 26.06.2020 03:11, Damien Le Moal wrote:
>> On 2020/06/26 2:18, Kanchan Joshi wrote:
>>> [Revised as per feedback from Damien, Pavel, Jens, Christoph, Matias, Wilcox]
>>>
>>> This patchset enables zone-append using io-uring/linux-aio, on block IO path.
>>> Purpose is to provide zone-append consumption ability to applications which are
>>> using zoned-block-device directly.
>>>
>>> The application may specify RWF_ZONE_APPEND flag with write when it wants to
>>> send zone-append. RWF_* flags work with a certain subset of APIs e.g. uring,
>>> aio, and pwritev2. An error is reported if zone-append is requested using
>>> pwritev2. It is not in the scope of this patchset to support pwritev2 or any
>>> other sync write API for reasons described later.
>>>
>>> Zone-append completion result --->
>>> With zone-append, where write took place can only be known after completion.
>>> So apart from usual return value of write, additional mean is needed to obtain
>>> the actual written location.
>>>
>>> In aio, this is returned to application using res2 field of io_event -
>>>
>>> struct io_event {
>>>         __u64           data;           /* the data field from the iocb */
>>>         __u64           obj;            /* what iocb this event came from */
>>>         __s64           res;            /* result code for this event */
>>>         __s64           res2;           /* secondary result */
>>> };
>>>
>>> In io-uring, cqe->flags is repurposed for zone-append result.
>>>
>>> struct io_uring_cqe {
>>>         __u64   user_data;      /* sqe->data submission passed back */
>>>         __s32   res;            /* result code for this event */
>>>         __u32   flags;
>>> };
>>>
>>> Since 32 bit flags is not sufficient, we choose to return zone-relative offset
>>> in sector/512b units. This can cover zone-size represented by chunk_sectors.
>>> Applications will have the trouble to combine this with zone start to know
>>> disk-relative offset. But if more bits are obtained by pulling from res field
>>> that too would compel application to interpret res field differently, and it
>>> seems more painstaking than the former option.
>>> To keep uniformity, even with aio, zone-relative offset is returned.
>>
>> I am really not a fan of this, to say the least. The input is byte offset, the
>> output is 512B relative sector count... Arg... We really cannot do better than
>> that ?
>>
>> At the very least, byte relative offset ? The main reason is that this is
>> _somewhat_ acceptable for raw block device accesses since the "sector"
>> abstraction has a clear meaning, but once we add iomap/zonefs async zone append
>> support, we really will want to have byte unit as the interface is regular
>> files, not block device file. We could argue that 512B sector unit is still
>> around even for files (e.g. block counts in file stat). Bu the different unit
>> for input and output of one operation is really ugly. This is not nice for the user.
>>
> 
> You can refer to the discussion with Jens, Pavel and Alex on the uring
> interface. With the bits we have and considering the maximun zone size
> supported, there is no space for a byte relative offset. We can take
> some bits from cqe->res, but we were afraid this is not very
> future-proof. Do you have a better idea?

If you can take 8 bits, that gives you 40 bits, enough to support byte relative
offsets for any zone size defined as a number of 512B sectors using an unsigned
int. Max zone size is 2^31 sectors in that case, so 2^40 bytes. Unless I am
already too tired and my math is failing me...

zone size is defined by chunk_sectors, which is used for raid and software raids
too. This has been an unsigned int forever. I do not see the need for changing
this to a 64bit anytime soon, if ever. A raid with a stripe size larger than 1TB
does not really make any sense. Same for zone size...

> 
> 
>>>
>>> Append using io_uring fixed-buffer --->
>>> This is flagged as not-supported at the moment. Reason being, for fixed-buffer
>>> io-uring sends iov_iter of bvec type. But current append-infra in block-layer
>>> does not support such iov_iter.
>>>
>>> Block IO vs File IO --->
>>> For now, the user zone-append interface is supported only for zoned-block-device.
>>> Regular files/block-devices are not supported. Regular file-system (e.g. F2FS)
>>> will not need this anyway, because zone peculiarities are abstracted within FS.
>>> At this point, ZoneFS also likes to use append implicitly rather than explicitly.
>>> But if/when ZoneFS starts supporting explicit/on-demand zone-append, the check
>>> allowing-only-block-device should be changed.
>>
>> Sure, but I think the interface is still a problem. I am not super happy about
>> the 512B sector unit. Zonefs will be the only file system that will be impacted
>> since other normal POSIX file system will not have zone append interface for
>> users. So this is a limited problem. Still, even for raw block device files
>> accesses, POSIX system calls use Byte unit everywhere. Let's try to use that.
>>
>> For aio, it is easy since res2 is unsigned long long. For io_uring, as discussed
>> already, we can still 8 bits from the cqe res. All  you need is to add a small
>> helper function in userspace iouring.h to simplify the work of the application
>> to get that result.
> 
> Ok. See above. We can do this.
> 
> Jens: Do you see this as a problem in the future?
> 
> [...]
> 
> Javier
> 


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH v2 0/2] zone-append support in io-uring and aio

[javier.gonz@samsung.com]

On 26.06.2020 06:56, Damien Le Moal wrote:
>On 2020/06/26 15:37, javier.gonz@samsung.com wrote:
>> On 26.06.2020 03:11, Damien Le Moal wrote:
>>> On 2020/06/26 2:18, Kanchan Joshi wrote:
>>>> [Revised as per feedback from Damien, Pavel, Jens, Christoph, Matias, Wilcox]
>>>>
>>>> This patchset enables zone-append using io-uring/linux-aio, on block IO path.
>>>> Purpose is to provide zone-append consumption ability to applications which are
>>>> using zoned-block-device directly.
>>>>
>>>> The application may specify RWF_ZONE_APPEND flag with write when it wants to
>>>> send zone-append. RWF_* flags work with a certain subset of APIs e.g. uring,
>>>> aio, and pwritev2. An error is reported if zone-append is requested using
>>>> pwritev2. It is not in the scope of this patchset to support pwritev2 or any
>>>> other sync write API for reasons described later.
>>>>
>>>> Zone-append completion result --->
>>>> With zone-append, where write took place can only be known after completion.
>>>> So apart from usual return value of write, additional mean is needed to obtain
>>>> the actual written location.
>>>>
>>>> In aio, this is returned to application using res2 field of io_event -
>>>>
>>>> struct io_event {
>>>>         __u64           data;           /* the data field from the iocb */
>>>>         __u64           obj;            /* what iocb this event came from */
>>>>         __s64           res;            /* result code for this event */
>>>>         __s64           res2;           /* secondary result */
>>>> };
>>>>
>>>> In io-uring, cqe->flags is repurposed for zone-append result.
>>>>
>>>> struct io_uring_cqe {
>>>>         __u64   user_data;      /* sqe->data submission passed back */
>>>>         __s32   res;            /* result code for this event */
>>>>         __u32   flags;
>>>> };
>>>>
>>>> Since 32 bit flags is not sufficient, we choose to return zone-relative offset
>>>> in sector/512b units. This can cover zone-size represented by chunk_sectors.
>>>> Applications will have the trouble to combine this with zone start to know
>>>> disk-relative offset. But if more bits are obtained by pulling from res field
>>>> that too would compel application to interpret res field differently, and it
>>>> seems more painstaking than the former option.
>>>> To keep uniformity, even with aio, zone-relative offset is returned.
>>>
>>> I am really not a fan of this, to say the least. The input is byte offset, the
>>> output is 512B relative sector count... Arg... We really cannot do better than
>>> that ?
>>>
>>> At the very least, byte relative offset ? The main reason is that this is
>>> _somewhat_ acceptable for raw block device accesses since the "sector"
>>> abstraction has a clear meaning, but once we add iomap/zonefs async zone append
>>> support, we really will want to have byte unit as the interface is regular
>>> files, not block device file. We could argue that 512B sector unit is still
>>> around even for files (e.g. block counts in file stat). Bu the different unit
>>> for input and output of one operation is really ugly. This is not nice for the user.
>>>
>>
>> You can refer to the discussion with Jens, Pavel and Alex on the uring
>> interface. With the bits we have and considering the maximun zone size
>> supported, there is no space for a byte relative offset. We can take
>> some bits from cqe->res, but we were afraid this is not very
>> future-proof. Do you have a better idea?
>
>If you can take 8 bits, that gives you 40 bits, enough to support byte relative
>offsets for any zone size defined as a number of 512B sectors using an unsigned
>int. Max zone size is 2^31 sectors in that case, so 2^40 bytes. Unless I am
>already too tired and my math is failing me...

Yes, the match is correct. I was thinking more of the bits being needed
for other use-case that could collide with append. We considered this
and discard it for being messy - when Pavel brought up the 512B
alignment we saw it as a good alternative.

Note too that we would be able to translate to a byte offset in
iouring.h too so the user would not need to think of this.

I do not feel strongly on this, so the one that better fits the current
and near-future for uring, that is the one we will send on V3. Will give
it until next week for others to comment too.

>
>zone size is defined by chunk_sectors, which is used for raid and software raids
>too. This has been an unsigned int forever. I do not see the need for changing
>this to a 64bit anytime soon, if ever. A raid with a stripe size larger than 1TB
>does not really make any sense. Same for zone size...

Yes. I think already max zone sizes are pretty huge. But yes, this might
change, so we will take it when it happens.

[...]

Javier

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

[Christoph Hellwig]

To restate my previous NAK:

A low-level protocol detail like RWF_ZONE_APPEND has absolutely no
business being exposed in the Linux file system interface.

And as mentioned before I think the idea of returning the actual
position written for O_APPEND writes totally makes sense, and actually
is generalizable to all files.  Together with zonefs that gives you a
perfect interface for zone append.

On Thu, Jun 25, 2020 at 10:45:48PM +0530, Kanchan Joshi wrote:
> Introduce RWF_ZONE_APPEND flag to represent zone-append.

And no one but us select few even know what zone append is, nevermind
what the detailed semantics are.  If you add a userspace API you need
to very clearly document the semantics inluding errors and corner cases.

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

[Kanchan Joshi]

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On Fri, Jun 26, 2020 at 09:58:46AM +0100, Christoph Hellwig wrote:
>To restate my previous NAK:
>
>A low-level protocol detail like RWF_ZONE_APPEND has absolutely no
>business being exposed in the Linux file system interface.
>
>And as mentioned before I think the idea of returning the actual
>position written for O_APPEND writes totally makes sense, and actually
>is generalizable to all files.  Together with zonefs that gives you a
>perfect interface for zone append.
>
>On Thu, Jun 25, 2020 at 10:45:48PM +0530, Kanchan Joshi wrote:
>> Introduce RWF_ZONE_APPEND flag to represent zone-append.
>
>And no one but us select few even know what zone append is, nevermind
>what the detailed semantics are.  If you add a userspace API you need
>to very clearly document the semantics inluding errors and corner cases.

For block IO path (which is the scope of this patchset) there is no
probelm in using RWF_APPEND for zone-append, because it does not do
anything for block device. We can use that, avoiding introduction of
RWF_ZONE_APPEND in user-space.

In kernel, will it be fine to keep IOCB_ZONE_APPEND apart from
IOCB_APPEND? Reason being, this can help to isolate the code meant only
for zone-append from the one that is already present for conventional
append.

Snippet from quick reference -

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;
+       }


As for file I/O in future, I see a potential problem with RWF_APPEND.
In io_uring, zone-append requires bit of pre/post processing, which
ideally should be done only for zone-append case. A ZoneFS file using
RWF_APPEND as a mean to invoke zone-append vs a regular file (hosted on
some other FS) requiring conventional RWF_APPEND - both will execute
that processing.
Is there a good way to differentiate ZoneFS file from another file which
only wants use conventional file-append?

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Re: [PATCH v2 0/2] zone-append support in io-uring and aio

[Kanchan Joshi]

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On Fri, Jun 26, 2020 at 03:11:55AM +0000, Damien Le Moal wrote:
>On 2020/06/26 2:18, Kanchan Joshi wrote:
>> Semantics --->
>> Zone-append, by its nature, may perform write on a different location than what
>> was specified. It does not fit into POSIX, and trying to fit may just undermine
>> its benefit. It may be better to keep semantics as close to zone-append as
>> possible i.e. specify zone-start location, and obtain the actual-write location
>> post completion. Towards that goal, existing async APIs seem to fit fine.
>> Async APIs (uring, linux aio) do not work on implicit write-pointer and demand
>> explicit write offset (which is what we need for append). Neither write-pointer
>
>What do you mean by "implicit write pointer" ? Are you referring to the behavior
>of AIO write with a block device file open with O_APPEND ? The yes, it does not
>work. But that is perfectly fine for regular files, that is for zonefs.
Sorry, I meant file pointer.
Yes, block-device opened with O_APPEND does not increase the file-pointer
to end-of-device. That said, for uring and aio, file-pointer position
plays no role, and it is application responsibility to pass the right write
location.
>I would prefer that this paragraph simply state the semantic that is implemented
>first. Then explain why the choice. But first, clarify how the API works, what
>is allowed, what's not etc. That will also simplify reviewing the code as one
>can then check the code against the goal.

In this path (block IO) there is hardly any scope/attempt to abstract away anything.
So raw zoned-storage rule/semantics apply. I expect zone-aware
applications, which are already aware of rules, to be consumer of this.

>> is taken as input, nor it is updated on completion. And there is a clear way to
>> get zone-append result. Zone-aware applications while using these async APIs
>> can be fine with, for the lack of better word, zone-append semantics itself.
>>
>> Sync APIs work with implicit write-pointer (at least few of those), and there is
>> no way to obtain zone-append result, making it hard for user-space zone-append.
>
>Sync API are executed under inode lock, at least for regular files. So there is
>absolutely no problem to use zone append. zonefs does it already. The problem is
>the lack of locking for block device file.
Yes. I was refering to the problem of returning actual write-location using
sync APIs like write, pwrite, pwritev/v2.
>>
>> Tests --->
>> Using new interface in fio (uring and libaio engine) by extending zbd tests
>> for zone-append: https://protect2.fireeye.com/url?k=e21dd5e0-bf837b7a-e21c5eaf-0cc47a336fae-c982437ed1be6cc8&q=1&u=https%3A%2F%2Fgithub.com%2Faxboe%2Ffio%2Fpull%2F1026
>>
>> Changes since v1:
>> - No new opcodes in uring or aio. Use RWF_ZONE_APPEND flag instead.
>> - linux-aio changes vanish because of no new opcode
>> - Fixed the overflow and other issues mentioned by Damien
>> - Simplified uring support code, fixed the issues mentioned by Pavel
>> - Added error checks
>>
>> Kanchan Joshi (1):
>>   fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path
>>
>> Selvakumar S (1):
>>   io_uring: add support for zone-append
>>
>>  fs/block_dev.c          | 28 ++++++++++++++++++++++++----
>>  fs/io_uring.c           | 32 ++++++++++++++++++++++++++++++--
>>  include/linux/fs.h      |  9 +++++++++
>>  include/uapi/linux/fs.h |  5 ++++-
>>  4 files changed, 67 insertions(+), 7 deletions(-)
>>
>
>
>-- 
>Damien Le Moal
>Western Digital Research
>

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

[Christoph Hellwig]

On Sat, Jun 27, 2020 at 02:45:14AM +0530, Kanchan Joshi wrote:
> For block IO path (which is the scope of this patchset) there is no
> probelm in using RWF_APPEND for zone-append, because it does not do
> anything for block device. We can use that, avoiding introduction of
> RWF_ZONE_APPEND in user-space.

No, you are not just touching the block I/O path.  This is all over the
general file code, and all RWF_* flag are about file I/O.

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

[Kanchan Joshi]

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On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
>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@samsung.com>
>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>> ---
>>  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 ?
REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
cleaner.
V3 will include the other changes you pointed out. Thanks for the review.


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

[Damien Le Moal]

On 2020/06/30 3:35, Kanchan Joshi wrote:
> On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
>> 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@samsung.com>
>>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>>> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>> ---
>>>  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 ?
> REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
> flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
> cleaner.
> V3 will include the other changes you pointed out. Thanks for the review.
> 

REQ_OP_WRITE and REQ_OP_ZONE_APPEND are different bits, so there is no
"override". A well formed BIO bi_opf is one op+flags. Specifying multiple OP
codes does not make sense.

-- 
Damien Le Moal
Western Digital Research

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

[Kanchan Joshi]

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On Tue, Jun 30, 2020 at 12:37:07AM +0000, Damien Le Moal wrote:
>On 2020/06/30 3:35, Kanchan Joshi wrote:
>> On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
>>> 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@samsung.com>
>>>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>>>> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
>>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>>> ---
>>>>  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 ?
>> REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
>> flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
>> cleaner.
>> V3 will include the other changes you pointed out. Thanks for the review.
>>
>
>REQ_OP_WRITE and REQ_OP_ZONE_APPEND are different bits, so there is no
>"override". A well formed BIO bi_opf is one op+flags. Specifying multiple OP
>codes does not make sense.

one op+flags behavior is retained here. OP is not about bits (op flags are).
Had it been, REQ_OP_WRITE (value 1) can not be differentiated from
REQ_OP_ZONE_APPEND (value 13).
We do not do "bio_op(bio) & REQ_OP_WRITE", rather we look at the
absolute value "bio_op(bio) == REQ_OP_WRITE".

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

[Damien Le Moal]

On 2020/06/30 16:43, Kanchan Joshi wrote:
> On Tue, Jun 30, 2020 at 12:37:07AM +0000, Damien Le Moal wrote:
>> On 2020/06/30 3:35, Kanchan Joshi wrote:
>>> On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
>>>> 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@samsung.com>
>>>>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>>>>> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
>>>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>>>> ---
>>>>>  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 ?
>>> REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
>>> flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
>>> cleaner.
>>> V3 will include the other changes you pointed out. Thanks for the review.
>>>
>>
>> REQ_OP_WRITE and REQ_OP_ZONE_APPEND are different bits, so there is no
>> "override". A well formed BIO bi_opf is one op+flags. Specifying multiple OP
>> codes does not make sense.
> 
> one op+flags behavior is retained here. OP is not about bits (op flags are).
> Had it been, REQ_OP_WRITE (value 1) can not be differentiated from
> REQ_OP_ZONE_APPEND (value 13).
> We do not do "bio_op(bio) & REQ_OP_WRITE", rather we look at the
> absolute value "bio_op(bio) == REQ_OP_WRITE".

Sure, the ops are not bits like the flags, but (excluding the flags) doing:

op |= REQ_OP_ZONE_APPEND;

will give you op == (REQ_OP_WRITE | REQ_OP_ZONE_APPEND). That's not what you want...



-- 
Damien Le Moal
Western Digital Research

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

[Damien Le Moal]

On 2020/06/30 16:53, Damien Le Moal wrote:
> On 2020/06/30 16:43, Kanchan Joshi wrote:
>> On Tue, Jun 30, 2020 at 12:37:07AM +0000, Damien Le Moal wrote:
>>> On 2020/06/30 3:35, Kanchan Joshi wrote:
>>>> On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
>>>>> 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@samsung.com>
>>>>>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>>>>>> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
>>>>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>>>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>>>>> ---
>>>>>>  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 ?
>>>> REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
>>>> flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
>>>> cleaner.
>>>> V3 will include the other changes you pointed out. Thanks for the review.
>>>>
>>>
>>> REQ_OP_WRITE and REQ_OP_ZONE_APPEND are different bits, so there is no
>>> "override". A well formed BIO bi_opf is one op+flags. Specifying multiple OP
>>> codes does not make sense.
>>
>> one op+flags behavior is retained here. OP is not about bits (op flags are).
>> Had it been, REQ_OP_WRITE (value 1) can not be differentiated from
>> REQ_OP_ZONE_APPEND (value 13).
>> We do not do "bio_op(bio) & REQ_OP_WRITE", rather we look at the
>> absolute value "bio_op(bio) == REQ_OP_WRITE".
> 
> Sure, the ops are not bits like the flags, but (excluding the flags) doing:
> 
> op |= REQ_OP_ZONE_APPEND;
> 
> will give you op == (REQ_OP_WRITE | REQ_OP_ZONE_APPEND). That's not what you want...

And yes, REQ_OP_WRITE | REQ_OP_ZONE_APPEND == REQ_OP_ZONE_APPEND... But still
not a reason for not setting the op correctly :)



-- 
Damien Le Moal
Western Digital Research

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

[Kanchan Joshi]

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On Tue, Jun 30, 2020 at 07:56:46AM +0000, Damien Le Moal wrote:
>On 2020/06/30 16:53, Damien Le Moal wrote:
>> On 2020/06/30 16:43, Kanchan Joshi wrote:
>>> On Tue, Jun 30, 2020 at 12:37:07AM +0000, Damien Le Moal wrote:
>>>> On 2020/06/30 3:35, Kanchan Joshi wrote:
>>>>> On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
>>>>>> 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@samsung.com>
>>>>>>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>>>>>>> Signed-off-by: Arnav Dawn <a.dawn@samsung.com>
>>>>>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>>>>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>>>>>> ---
>>>>>>>  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 ?
>>>>> REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
>>>>> flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
>>>>> cleaner.
>>>>> V3 will include the other changes you pointed out. Thanks for the review.
>>>>>
>>>>
>>>> REQ_OP_WRITE and REQ_OP_ZONE_APPEND are different bits, so there is no
>>>> "override". A well formed BIO bi_opf is one op+flags. Specifying multiple OP
>>>> codes does not make sense.
>>>
>>> one op+flags behavior is retained here. OP is not about bits (op flags are).
>>> Had it been, REQ_OP_WRITE (value 1) can not be differentiated from
>>> REQ_OP_ZONE_APPEND (value 13).
>>> We do not do "bio_op(bio) & REQ_OP_WRITE", rather we look at the
>>> absolute value "bio_op(bio) == REQ_OP_WRITE".
>>
>> Sure, the ops are not bits like the flags, but (excluding the flags) doing:
>>
>> op |= REQ_OP_ZONE_APPEND;
>>
>> will give you op == (REQ_OP_WRITE | REQ_OP_ZONE_APPEND). That's not what you want...
>
>And yes, REQ_OP_WRITE | REQ_OP_ZONE_APPEND == REQ_OP_ZONE_APPEND... But still
>not a reason for not setting the op correctly :)
Right, this is what op override was about, and intent was to minimize
the changes in the existing function. As said before, completely agree about
changing, code should not draw suspicion. 

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Re: [PATCH v2 0/2] zone-append support in io-uring and aio

[Matthew Wilcox]

On Thu, Jun 25, 2020 at 10:45:47PM +0530, Kanchan Joshi wrote:
> Zone-append completion result --->
> With zone-append, where write took place can only be known after completion.
> So apart from usual return value of write, additional mean is needed to obtain
> the actual written location.
> 
> In aio, this is returned to application using res2 field of io_event -
> 
> struct io_event {
>         __u64           data;           /* the data field from the iocb */
>         __u64           obj;            /* what iocb this event came from */
>         __s64           res;            /* result code for this event */
>         __s64           res2;           /* secondary result */
> };

Ah, now I understand.  I think you're being a little too specific by
calling this zone-append.  This is really a "write-anywhere" operation,
and the specified address is only a hint.

> In io-uring, cqe->flags is repurposed for zone-append result.
> 
> struct io_uring_cqe {
>         __u64   user_data;      /* sqe->data submission passed back */
>         __s32   res;            /* result code for this event */
>         __u32   flags;
> };
> 
> Since 32 bit flags is not sufficient, we choose to return zone-relative offset
> in sector/512b units. This can cover zone-size represented by chunk_sectors.
> Applications will have the trouble to combine this with zone start to know
> disk-relative offset. But if more bits are obtained by pulling from res field
> that too would compel application to interpret res field differently, and it
> seems more painstaking than the former option.
> To keep uniformity, even with aio, zone-relative offset is returned.

Urgh, no, that's dreadful.  I'm not familiar with the io_uring code.
Maybe the first 8 bytes of the user_data could be required to be the
result offset for this submission type?

> Block IO vs File IO --->
> For now, the user zone-append interface is supported only for zoned-block-device.
> Regular files/block-devices are not supported. Regular file-system (e.g. F2FS)
> will not need this anyway, because zone peculiarities are abstracted within FS.
> At this point, ZoneFS also likes to use append implicitly rather than explicitly.
> But if/when ZoneFS starts supporting explicit/on-demand zone-append, the check
> allowing-only-block-device should be changed.

But we also have O_APPEND files.  And maybe we'll have other kinds of file
in future for which this would make sense.

> Semantics --->
> Zone-append, by its nature, may perform write on a different location than what
> was specified. It does not fit into POSIX, and trying to fit may just undermine

... I disagree that it doesn't fit into POSIX.  As I said above, O_APPEND
is a POSIX concept, so POSIX already understands that writes may not end
up at the current write pointer.

> its benefit. It may be better to keep semantics as close to zone-append as
> possible i.e. specify zone-start location, and obtain the actual-write location
> post completion. Towards that goal, existing async APIs seem to fit fine.
> Async APIs (uring, linux aio) do not work on implicit write-pointer and demand
> explicit write offset (which is what we need for append). Neither write-pointer
> is taken as input, nor it is updated on completion. And there is a clear way to
> get zone-append result. Zone-aware applications while using these async APIs
> can be fine with, for the lack of better word, zone-append semantics itself.
> 
> Sync APIs work with implicit write-pointer (at least few of those), and there is
> no way to obtain zone-append result, making it hard for user-space zone-append.