[PATCH] Use io_uring_register_ring_fd() to skip fd operations

[Sam Li]

Linux recently added a new io_uring(7) optimization API that QEMU
doesn't take advantage of yet. The liburing library that QEMU uses
has added a corresponding new API calling io_uring_register_ring_fd().
When this API is called after creating the ring, the io_uring_submit()
library function passes a flag to the io_uring_enter(2) syscall
allowing it to skip the ring file descriptor fdget()/fdput()
operations. This saves some CPU cycles.

Signed-off-by: Sam Li <faithilike...@gmail.com>
---
 block/io_uring.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/io_uring.c b/block/io_uring.c
index 782afdb433..2942967126 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -435,6 +435,9 @@ LuringState *luring_init(Error **errp)
     }
 
     ioq_init(&s->io_q);
+    if (io_uring_register_ring_fd(&s->ring) < 0) {
+        error_setg_errno(errp, errno, "failed to register linux
 io_uring ring file descriptor");
+    }
     return s;
 
 }
-- 
2.35.1