[PATCH 15/15] io_uring: add io_uring_event cache hit information

[Jens Axboe]

Add hint on whether a read was served out of the page cache, or if it
hit media. This is useful for buffered async IO, O_DIRECT reads would
never have this set (for obvious reasons).

If the read hit page cache, cqe->flags will have IOCQE_FLAG_CACHEHIT
set.

Signed-off-by: Jens Axboe <ax...@kernel.dk>
---
 fs/io_uring.c                 | 7 ++++++-
 include/uapi/linux/io_uring.h | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6c62329b00ec..f2a603c447ba 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -511,11 +511,16 @@ static void io_fill_cq_error(struct io_ring_ctx *ctx, 
struct sqe_submit *s,
 static void io_complete_scqring_rw(struct kiocb *kiocb, long res, long res2)
 {
        struct io_kiocb *iocb = container_of(kiocb, struct io_kiocb, rw);
+       unsigned ev_flags = 0;
 
        kiocb_end_write(kiocb);
 
        fput(kiocb->ki_filp);
-       io_cqring_fill_event(iocb->ki_ctx, iocb->ki_index, res, 0);
+
+       if (res > 0 && test_bit(KIOCB_F_FORCE_NONBLOCK, &iocb->ki_flags))
+               ev_flags = IOCQE_FLAG_CACHEHIT;
+
+       io_cqring_fill_event(iocb->ki_ctx, iocb->ki_index, res, ev_flags);
        io_free_kiocb(iocb);
 }
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 9321eb97479d..20e4c22e040d 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -55,6 +55,11 @@ struct io_uring_cqe {
        __u32   flags;
 };
 
+/*
+ * io_uring_event->flags
+ */
+#define IOCQE_FLAG_CACHEHIT    (1 << 0)        /* IO did not hit media */
+
 /*
  * Magic offsets for the application to mmap the data it needs
  */
-- 
2.17.1