It is common for an application using an ever-evolving interface to want
to inquire about the presence of certain functionality it plans to use.
The boilerplate to do that is about always the same: find places that
have feature bits, match that with what we need, rinse, repeat.
Therefore it makes sense to move this to a library function.
We have two places in which we can check for such features: the feature
flag returned by io_uring_init_params(), and the resulting array
returning from io_uring_probe.
I tried my best to communicate as well as possible in the function
signature the fact that this is not supposed to test the availability
of io_uring (which is straightforward enough), but rather a minimum set
of requirements for usage.
Signed-off-by: Glauber Costa <glauber@xxxxxxxxxxxx>
CC: Avi Kivity <avi@xxxxxxxxxxxx>
---
src/include/liburing.h | 13 +++++++++++++
src/liburing.map | 1 +
src/setup.c | 39 +++++++++++++++++++++++++++++++++++++++
3 files changed, 53 insertions(+)
diff --git a/src/include/liburing.h b/src/include/liburing.h
index 83d11dd..d740083 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -72,6 +72,19 @@ struct io_uring {
/*
* Library interface
*/
+
+/* Checks that io_uring is modern enough for a particular case.
+ * Check it by verifying that:
+ *
+ * - io_uring is available
+ * - the io_uring_probe call is available, so opcodes can be checked
+ * - all opcodes the application wants to use are supported
+ * - the features requested are present.
+ *
+ * return 0 if io_uring is not usable, 1 otherwise.
+ */
+extern int io_uring_check_minimum_support(const int* operations, int noperations, int features);
+
extern int io_uring_queue_init_params(unsigned entries, struct io_uring *ring,
struct io_uring_params *p);
extern int io_uring_queue_init(unsigned entries, struct io_uring *ring,
diff --git a/src/liburing.map b/src/liburing.map
index b45f373..579d4de 100644
--- a/src/liburing.map
+++ b/src/liburing.map
@@ -72,4 +72,5 @@ LIBURING_0.4 {
io_uring_register_probe;
io_uring_register_personality;
io_uring_unregister_personality;
+ io_uring_check_minimum_support;
} LIBURING_0.3;
diff --git a/src/setup.c b/src/setup.c
index c53f234..7e46219 100644
--- a/src/setup.c
+++ b/src/setup.c
@@ -4,6 +4,7 @@
#include <unistd.h>
#include <errno.h>
#include <string.h>
+#include <stdlib.h>
#include "liburing/compat.h"
#include "liburing/io_uring.h"
@@ -167,3 +168,41 @@ void io_uring_queue_exit(struct io_uring *ring)
io_uring_unmap_rings(sq, cq);
close(ring->ring_fd);
}
+
+int io_uring_check_minimum_support(const int* operations, int noperations, int features)
+{
+ struct io_uring_params p;
+ struct io_uring_probe* probe;
+ struct io_uring ring;
+ int r;
+ int i;
+ int ret = 0;
+
+ memset(&p, 0, sizeof(p));
+ r = io_uring_queue_init_params(2, &ring, &p);
+ if (r < 0)
+ return ret;
+
+ if ((p.features & features) != features)
+ goto exit;
+
+ size_t len = sizeof(*probe) + 256 * sizeof(struct io_uring_probe_op);
+ probe = malloc(len);
+ memset(probe, 0, len);
+ r = io_uring_register_probe(&ring, probe, 256);
+ if (r < 0)
+ goto exit;
+
+ for (i = 0; i < noperations; i++) {
+ int op = operations[i];
+ if (probe->last_op < op)
+ goto exit;
+
+ if (!(probe->ops[op].flags & IO_URING_OP_SUPPORTED))
+ goto exit;
+ }
+ ret = 1;
+exit:
+ io_uring_queue_exit(&ring);
+ return ret;
+}
--
2.20.1
