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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: 李通洲 <carter.li@eoitek.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2019-12-25 16:33:42 -07:00
parent 3a6820f2bb
commit ba04291eb6
2 changed files with 11 additions and 1 deletions
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11
fs/io_uring.c
View File

@ -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:

1
include/uapi/linux/io_uring.h
View File

@ -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