io_uring_setup_buf_ring(3)

NAME
io_uring_setup_buf_ring - setup and register buffer ring for provided buffers

SYNOPSIS
#include <liburing.h>

struct io_uring_buf_ring *io_uring_setup_buf_ring(struct io_uring *ring,
                                                  unsigned int nentries,
                                                  int bgid,
                                                  unsigned int flags,
                                                  int *err);

DESCRIPTION

The io_uring_setup_buf_ring(3) function registers a shared buffer ring to be used with provided buffers. For the request types that support it, provided buffers are given to the ring and one is selected by a request if it has IOSQE_BUFFER_SELECT set in the SQE flags, when the request is ready to receive data. This allows both clear ownership of the buffer lifetime, and a way to have more read/receive type of operations in flight than buffers available.

The ring argument must be a pointer to the ring for which the provided buffer ring is being registered, nentries is the number of entries requested in the buffer ring. This argument must be a power-of 2 in size, and can be up to 32768 in size. bgid is the chosen buffer group ID, flags are modifier flags for the operation, and *err is a pointer to an integer for the error value if any part of the ring allocation and registration fails.

The flags argument can be set to one of the following values:

IOU_PBUF_RING_INC
    The buffers in this ring can be incrementally consumed. With partial consumption, each completion of a given buffer ID will continue where the previous one left off, or from the start if no completions have been seen yet. When more completions should be expected for a given buffer ID, the CQE will have IORING_CQE_F_BUF_MORE set in the flags member. Available since 6.12.

Under the covers, this function uses io_uring_register_buf_ring(3) to register the ring, and handles the allocation of the ring rather than letting the application open code it.

To unregister and free a buffer group ID setup with this function, the application must call io_uring_free_buf_ring(3).

Available since 5.19.

RETURN VALUE
On success io_uring_setup_buf_ring(3) returns a pointer to the buffer ring. On failure it returns NULL and sets *err to -errno.

NOTES
Note that even if the kernel supports this feature, registering a provided buffer ring may still fail with -EINVAL if the host is a 32-bit architecture and the memory being passed in resides in high memory.

SEE ALSO
io_uring_register_buf_ring(3), io_uring_buf_ring_init(3), io_uring_buf_ring_add(3), io_uring_buf_ring_advance(3), io_uring_buf_ring_cq_advance(3)