ioq: Check for io_uring_register_iowq_max_workers() before using it

This allows us to build against liburing as old as version 2.0, which is
apparently shipped by the latest Amazon Linux distribution.

Fixes: https://github.com/tavianator/bfs/issues/147

3 files changed, 15 insertions, 0 deletions

diff --git a/build/has/io-uring-max-workers.c b/build/has/io-uring-max-workers.c
new file mode 100644
index 0000000..34ab5b7
--- /dev/null
+++ b/build/has/io-uring-max-workers.c
@@ -0,0 +1,11 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+#include <liburing.h>
+
+int main(void) {
+	struct io_uring ring;
+	io_uring_queue_init(1, &ring, 0);
+	unsigned int values[] = {0, 0};
+	return io_uring_register_iowq_max_workers(&ring, values);
+}
diff --git a/build/header.mk b/build/header.mk
index e9f1abc..f940e52 100644
--- a/build/header.mk
+++ b/build/header.mk
@@ -33,6 +33,7 @@ HEADERS := \
     gen/has/getmntinfo.h \
     gen/has/getprogname-gnu.h \
     gen/has/getprogname.h \
+    gen/has/io-uring-max-workers.h \
     gen/has/pipe2.h \
     gen/has/posix-getdents.h \
     gen/has/posix-spawn-addfchdir-np.h \
diff --git a/src/ioq.c b/src/ioq.c
index f936ff8..be5b758 100644
--- a/src/ioq.c
+++ b/src/ioq.c
@@ -878,6 +878,7 @@ static int ioq_ring_init(struct ioq *ioq, struct ioq_thread *thread) {
 		return -1;
 	}
 
+#if BFS_HAS_IO_URING_MAX_WORKERS
 	// Limit the number of io_uring workers
 	unsigned int values[] = {
 		ioq->nthreads, // [IO_WQ_BOUND]
@@ -886,6 +887,8 @@ static int ioq_ring_init(struct ioq *ioq, struct ioq_thread *thread) {
 	io_uring_register_iowq_max_workers(&thread->ring, values);
 #endif
 
+#endif // BFS_WITH_LIBURING
+
 	return 0;
 }