.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_buf_ring_available 3 "Jan 11, 2024" "liburing-2.6" "liburing Manual"
.SH NAME
io_uring_buf_ring_available \- return number of unconsumed provided ring buffer entries
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "int io_uring_buf_ring_available(struct io_uring *" ring ",
.BI "                                struct io_uring_buf_ring *" br ",
.BI "                                unsigned short " bgid ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_buf_ring_available (3)
helper returns the number of unconsumed (by the kernel) entries in the
.IR br
provided buffer group belonging to the io_uring
.IR ring
and identified by the buffer group ID
.IR 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.

.SH NOTES
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.
.SH RETURN VALUE
Returns the number of unconsumed entries on success, which may be 0. In case
of error, may return
.BR -ENOENT
if the specified buffer group doesn't exist, or
.BR -EINVAL
if the buffer group isn't of the correct type, or if the kernel doesn't
support this feature.
.SH SEE ALSO
.BR io_uring_register_buf_ring (3),
.BR io_uring_buf_ring_add (3),
.BR io_uring_buf_ring_cq_advance (3)