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>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 407ba33..5286620 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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:

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 7fdf994..1f96136 100644 (file)
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -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