io_uring_buf_ring_available(3) liburing Manual io_uring_buf_ring_available(3)

io_uring_buf_ring_available - return number of unconsumed provided ring buffer entries

#include <liburing.h>
int io_uring_buf_ring_available(struct io_uring *ring,
                                struct io_uring_buf_ring *br,
                                unsigned short bgid);

The io_uring_buf_ring_available(3) helper returns the number of unconsumed (by the kernel) entries in the br provided buffer group belonging to the io_uring ring and identified by the buffer group ID bgid.

Since the head of the provided buffer ring is only visible to the kernel, it's impossible to otherwise know how many unconsumed entries exist in the given provided buffer ring. This function query the kernel to return that number.

The returned number of entries reflect the amount of unconsumed entries at the time that it was queried. If inflight IO exists that may consume provided buffers from this buffer group, then the returned value is inherently racy.

Returns the number of unconsumed entries on success, which may be 0. In case of error, may return -ENOENT if the specified buffer group doesn't exist, or -EINVAL if the buffer group isn't of the correct type, or if the kernel doesn't support this feature.

io_uring_register_buf_ring(3), io_uring_buf_ring_add(3), io_uring_buf_ring_cq_advance(3)

January 11, 2024 liburing-2.6