Commit ba04291e authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring: allow use of offset == -1 to mean file position 



This behaves like preadv2/pwritev2 with offset == -1, it'll use (and
update) the current file position. This obviously comes with the caveat
that if the application has multiple read/writes in flight, then the
end result will not be as expected. This is similar to threads sharing
a file descriptor and doing IO using the current file position.

Since this feature isn't easily detectable by doing a read or write,
add a feature flags, IORING_FEAT_RW_CUR_POS, to allow applications to
detect presence of this feature.

Reported-by: default avatar李通洲 <carter.li@eoitek.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 3a6820f2

fs/io_uring.c

+10 −1
Original line number Diff line number Diff line
@@ -495,6 +495,7 @@ struct io_kiocb { 
#define REQ_F_COMP_LOCKED	32768	/* completion under lock */

#define REQ_F_HARDLINK		65536	/* doesn't sever on completion < 0 */

#define REQ_F_FORCE_ASYNC	131072	/* IOSQE_ASYNC */

#define REQ_F_CUR_POS		262144	/* read/write uses file position */

	u64			user_data;

	u32			result;

	u32			sequence;
@@ -1711,6 +1712,10 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe, 
		req->flags |= REQ_F_ISREG;



	kiocb->ki_pos = READ_ONCE(sqe->off);

	if (kiocb->ki_pos == -1 && !(req->file->f_mode & FMODE_STREAM)) {

		req->flags |= REQ_F_CUR_POS;

		kiocb->ki_pos = req->file->f_pos;

	}

	kiocb->ki_flags = iocb_flags(kiocb->ki_filp);

	kiocb->ki_hint = ki_hint_validate(file_write_hint(kiocb->ki_filp));
@@ -1782,6 +1787,10 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret) 
static void kiocb_done(struct kiocb *kiocb, ssize_t ret, struct io_kiocb **nxt,

		       bool in_async)

{

	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);



	if (req->flags & REQ_F_CUR_POS)

		req->file->f_pos = kiocb->ki_pos;

	if (in_async && ret >= 0 && kiocb->ki_complete == io_complete_rw)

		*nxt = __io_complete_rw(kiocb, ret);

	else
@@ -6154,7 +6163,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p) 
		goto err;



	p->features = IORING_FEAT_SINGLE_MMAP | IORING_FEAT_NODROP |

			IORING_FEAT_SUBMIT_STABLE;

			IORING_FEAT_SUBMIT_STABLE | IORING_FEAT_RW_CUR_POS;

	trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);

	return ret;

err:

include/uapi/linux/io_uring.h

+1 −0
Original line number Diff line number Diff line
@@ -174,6 +174,7 @@ struct io_uring_params { 
#define IORING_FEAT_SINGLE_MMAP		(1U << 0)

#define IORING_FEAT_NODROP		(1U << 1)

#define IORING_FEAT_SUBMIT_STABLE	(1U << 2)

#define IORING_FEAT_RW_CUR_POS		(1U << 3)



/*

 * io_uring_register(2) opcodes and arguments

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