[PATCH liburing 2/2] setup: default to IORING_SETUP_NO_SQARRAY

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

We have never exposed sq_array to users, so we can safely add
IORING_SETUP_NO_SQARRAY to all rings. If the kernel is too old and it
fails, we'll retry creating a ring without it.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 src/setup.c           | 28 +++++++++++++++++++++++-----
 test/accept-reuse.c   |  2 +-
 test/helpers.h        | 13 +++++++++++++
 test/io_uring_enter.c |  7 +++++--
 4 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/src/setup.c b/src/setup.c
index a0e8296..6b3f538 100644
--- a/src/setup.c
+++ b/src/setup.c
@@ -287,9 +287,9 @@ static int io_uring_alloc_huge(unsigned entries, struct io_uring_params *p,
 	return (int) mem_used;
 }
 
-static int __io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
-					struct io_uring_params *p, void *buf,
-					size_t buf_size)
+int __io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
+				 struct io_uring_params *p, void *buf,
+				 size_t buf_size)
 {
 	int fd, ret = 0;
 	unsigned *sq_array;
@@ -357,6 +357,24 @@ static int __io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
 	return ret;
 }
 
+static int io_uring_queue_init_try_nosqarr(unsigned entries, struct io_uring *ring,
+					   struct io_uring_params *p, void *buf,
+					   size_t buf_size)
+{
+	unsigned flags = p->flags;
+	int ret;
+
+	p->flags |= IORING_SETUP_NO_SQARRAY;
+	ret = __io_uring_queue_init_params(entries, ring, p, buf, buf_size);
+
+	/* don't fallback if explicitly asked for NOSQARRAY */
+	if (ret != -EINVAL || (flags & IORING_SETUP_NO_SQARRAY))
+		return ret;
+
+	p->flags = flags;
+	return __io_uring_queue_init_params(entries, ring, p, buf, buf_size);
+}
+
 /*
  * Like io_uring_queue_init_params(), except it allows the application to pass
  * in a pre-allocated memory range that is used for the shared data between
@@ -375,7 +393,7 @@ int io_uring_queue_init_mem(unsigned entries, struct io_uring *ring,
 {
 	/* should already be set... */
 	p->flags |= IORING_SETUP_NO_MMAP;
-	return __io_uring_queue_init_params(entries, ring, p, buf, buf_size);
+	return io_uring_queue_init_try_nosqarr(entries, ring, p, buf, buf_size);
 }
 
 int io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
@@ -383,7 +401,7 @@ int io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
 {
 	int ret;
 
-	ret = __io_uring_queue_init_params(entries, ring, p, NULL, 0);
+	ret = io_uring_queue_init_try_nosqarr(entries, ring, p, NULL, 0);
 	return ret >= 0 ? 0 : ret;
 }
 
diff --git a/test/accept-reuse.c b/test/accept-reuse.c
index 1f10b45..716f201 100644
--- a/test/accept-reuse.c
+++ b/test/accept-reuse.c
@@ -45,7 +45,7 @@ int main(int argc, char **argv)
 		return T_EXIT_SKIP;
 
 	memset(&params, 0, sizeof(params));
-	ret = io_uring_queue_init_params(4, &io_uring, &params);
+	ret = t_io_uring_init_sqarray(4, &io_uring, &params);
 	if (ret) {
 		fprintf(stderr, "io_uring_init_failed: %d\n", ret);
 		return T_EXIT_FAIL;
diff --git a/test/helpers.h b/test/helpers.h
index 5307324..d91c1dc 100644
--- a/test/helpers.h
+++ b/test/helpers.h
@@ -87,6 +87,19 @@ bool t_probe_defer_taskrun(void);
 
 unsigned __io_uring_flush_sq(struct io_uring *ring);
 
+int __io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
+				 struct io_uring_params *p, void *buf,
+				 size_t buf_size);
+
+static inline int t_io_uring_init_sqarray(unsigned entries, struct io_uring *ring,
+					struct io_uring_params *p)
+{
+	int ret;
+
+	ret = __io_uring_queue_init_params(entries, ring, p, NULL, 0);
+	return ret >= 0 ? 0 : ret;
+}
+
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 
 void t_error(int status, int errnum, const char *format, ...);
diff --git a/test/io_uring_enter.c b/test/io_uring_enter.c
index ecd54ff..2a6b6be 100644
--- a/test/io_uring_enter.c
+++ b/test/io_uring_enter.c
@@ -183,13 +183,16 @@ int main(int argc, char **argv)
 	unsigned ktail, mask, index;
 	unsigned sq_entries;
 	unsigned completed, dropped;
+	struct io_uring_params p;
 
 	if (argc > 1)
 		return T_EXIT_SKIP;
 
-	ret = io_uring_queue_init(IORING_MAX_ENTRIES, &ring, 0);
+	memset(&p, 0, sizeof(p));
+	ret = t_io_uring_init_sqarray(IORING_MAX_ENTRIES, &ring, &p);
 	if (ret == -ENOMEM)
-		ret = io_uring_queue_init(IORING_MAX_ENTRIES_FALLBACK, &ring, 0);
+		ret = t_io_uring_init_sqarray(IORING_MAX_ENTRIES_FALLBACK,
+					      &ring, &p);
 	if (ret < 0) {
 		perror("io_uring_queue_init");
 		exit(T_EXIT_FAIL);
-- 
2.41.0