Add support for ring resizing

io_uring_resize_rings() support resizing the SQ and CQ rings, where
the most useful case here is resizing the CQ ring. This can be useful
for cases where users of a ring don't have a good idea of how busy it
will be. Rather than start with a big ring, they can start small for
the most common use cases, and enlarge it if needed if/when overflows
are seen.

Usage:

struct io_uring_params p = { };

p.sq_entries = new_sq_entries;
p.cq_entries = new_cq_entries;

io_uring_resize_rings(ring, &p);

where 'new_sq_entries' is the new value for the size of the SQ ring,
and 'new_cq_entries' is the new value for the size of the CQ ring.

Signed-off-by: Jens Axboe <[email protected]>

src/include/liburing.h

@@ -197,6 +197,7 @@ int io_uring_submit_and_wait_min_timeout(struct io_uring *ring,
 					 unsigned min_wait,
 					 sigset_t *sigmask);
 
+int io_uring_resize_rings(struct io_uring *ring, struct io_uring_params *p);
 int io_uring_clone_buffers(struct io_uring *dst, struct io_uring *src);
 int io_uring_register_buffers(struct io_uring *ring, const struct iovec *iovecs,
 			      unsigned nr_iovecs);

src/include/liburing/io_uring.h

@@ -612,6 +612,8 @@ enum io_uring_register_op {
 	/* clone registered buffers from source ring to current ring */
 	IORING_REGISTER_CLONE_BUFFERS		= 30,
 
+	IORING_REGISTER_RESIZE_RINGS		= 33,
+
 	/* this goes last */
 	IORING_REGISTER_LAST,
 

src/liburing-ffi.map

@@ -214,4 +214,5 @@ LIBURING_2.8 {
 		io_uring_prep_cmd_discard;
 		io_uring_prep_open;
 		io_uring_prep_open_direct;
+		io_uring_resize_rings;
 } LIBURING_2.7;

src/liburing.map

@@ -102,4 +102,5 @@ LIBURING_2.8 {
 		io_uring_submit_and_wait_min_timeout;
 		io_uring_wait_cqes_min_timeout;
 		io_uring_clone_buffers;
+		io_uring_resize_rings;
 } LIBURING_2.7;

src/register.c

@@ -4,6 +4,7 @@
 #include "lib.h"
 #include "syscall.h"
 #include "liburing.h"
+#include "setup.h"
 #include "int_flags.h"
 #include "liburing/compat.h"
 #include "liburing/io_uring.h"
@@ -408,3 +409,38 @@ int io_uring_clone_buffers(struct io_uring *dst, struct io_uring *src)
 
 	return do_register(dst, IORING_REGISTER_CLONE_BUFFERS, &buf, 1);
 }
+
+int io_uring_resize_rings(struct io_uring *ring, struct io_uring_params *p)
+{
+	unsigned sq_entries;
+	int ret;
+
+	ret = do_register(ring, IORING_REGISTER_RESIZE_RINGS, p, 1);
+	if (ret < 0)
+		return ret;
+
+	io_uring_unmap_rings(&ring->sq, &ring->cq);
+	if (!(p->flags & IORING_SETUP_NO_MMAP)) {
+		ret = io_uring_mmap(ring->ring_fd, p, &ring->sq, &ring->cq);
+		if (ret)
+			return ret;
+	} else {
+		io_uring_setup_ring_pointers(p, &ring->sq, &ring->cq);
+	}
+
+	/*
+	 * Directly map SQ slots to SQEs
+	 */
+	sq_entries = ring->sq.ring_entries;
+
+	if (!(p->flags & IORING_SETUP_NO_SQARRAY)) {
+		unsigned *sq_array;
+		unsigned index;
+
+		sq_array = ring->sq.array;
+		for (index = 0; index < sq_entries; index++)
+			sq_array[index] = index;
+	}
+
+	return 0;
+}

src/setup.c

@@ -59,17 +59,17 @@ static int get_sq_cq_entries(unsigned entries, struct io_uring_params *p,
 	return 0;
 }
 
-static void io_uring_unmap_rings(struct io_uring_sq *sq, struct io_uring_cq *cq)
+void io_uring_unmap_rings(struct io_uring_sq *sq, struct io_uring_cq *cq)
 {
 	if (sq->ring_sz)
 		__sys_munmap(sq->ring_ptr, sq->ring_sz);
 	if (cq->ring_ptr && cq->ring_sz && cq->ring_ptr != sq->ring_ptr)
 		__sys_munmap(cq->ring_ptr, cq->ring_sz);
 }
 
-static void io_uring_setup_ring_pointers(struct io_uring_params *p,
-					 struct io_uring_sq *sq,
-					 struct io_uring_cq *cq)
+void io_uring_setup_ring_pointers(struct io_uring_params *p,
+				  struct io_uring_sq *sq,
+				  struct io_uring_cq *cq)
 {
 	sq->khead = sq->ring_ptr + p->sq_off.head;
 	sq->ktail = sq->ring_ptr + p->sq_off.tail;
@@ -95,8 +95,8 @@ static void io_uring_setup_ring_pointers(struct io_uring_params *p,
 	cq->ring_entries = *cq->kring_entries;
 }
 
-static int io_uring_mmap(int fd, struct io_uring_params *p,
-			 struct io_uring_sq *sq, struct io_uring_cq *cq)
+int io_uring_mmap(int fd, struct io_uring_params *p, struct io_uring_sq *sq,
+		  struct io_uring_cq *cq)
 {
 	size_t size;
 	int ret;

src/setup.h

@@ -5,5 +5,11 @@
 int __io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
 				 struct io_uring_params *p, void *buf,
 				 size_t buf_size);
+void io_uring_unmap_rings(struct io_uring_sq *sq, struct io_uring_cq *cq);
+int io_uring_mmap(int fd, struct io_uring_params *p, struct io_uring_sq *sq,
+		  struct io_uring_cq *cq);
+void io_uring_setup_ring_pointers(struct io_uring_params *p,
+				  struct io_uring_sq *sq,
+				  struct io_uring_cq *cq);
 
 #endif