io_uring_buf_ring_cq_advance(3) liburing Manual io_uring_buf_ring_cq_advance(3)

io_uring_buf_ring_cq_advance - advance index of provided buffer and CQ ring

#include <liburing.h>
void io_uring_buf_ring_cq_advance(struct io_uring *ring,
                                  struct io_uring_buf_ring *br,
                                  int count);
void __io_uring_buf_ring_cq_advance(struct io_uring *ring,
                                    struct io_uring_buf_ring *br,
                                    int cq_count,
                                    int buf_count);

The io_uring_buf_ring_cq_advance(3) commits count previously added buffers to the shared buffer ring br, making them visible to the kernel and hence consumable. This passes ownership of the buffer to the ring. At the same time, it advances the CQ ring of ring by count amount. This effectively bundles both a io_uring_buf_ring_advance(3) call and a io_uring_cq_advance(3) into one operation. Since updating either ring index entails a store memory barrier, doing both at once is more efficient.

The __io_uring_buf_ring_cq_advance(3) function performs the same operation, except it splits the counts into two separate values. It advances the CQ ring by cq_count entries, and the buffer ring by buf_count entries rather than increment both by the same value.


io_uring_register_buf_ring(3), io_uring_buf_ring_add(3), io_uring_buf_ring_advance(3)

May 18, 2022 liburing-2.2