aio-posix: signal-proof fdmon-io_uring

The io_uring_enter(2) syscall returns with errno=EINTR when interrupted
by a signal.  Retry the syscall in this case.

It's essential to do this in the io_uring_submit_and_wait() case.  My
interpretation of the Linux v5.5 io_uring_enter(2) code is that it
shouldn't affect the io_uring_submit() case, but there is no guarantee
this will always be the case.  Let's check for -EINTR around both APIs.

Note that the liburing APIs have -errno return values.

Signed-off-by: Stefan Hajnoczi <[email protected]>
Reviewed-by: Stefano Garzarella <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: [email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>

Author: stefanhaRH

util/fdmon-io_uring.c

@@ -88,7 +88,10 @@ static struct io_uring_sqe *get_sqe(AioContext *ctx)
     }
 
     /* No free sqes left, submit pending sqes first */
-    ret = io_uring_submit(ring);
+    do {
+        ret = io_uring_submit(ring);
+    } while (ret == -EINTR);
+
     assert(ret > 1);
     sqe = io_uring_get_sqe(ring);
     assert(sqe);
@@ -282,7 +285,10 @@ static int fdmon_io_uring_wait(AioContext *ctx, AioHandlerList *ready_list,
 
     fill_sq_ring(ctx);
 
-    ret = io_uring_submit_and_wait(&ctx->fdmon_io_uring, wait_nr);
+    do {
+        ret = io_uring_submit_and_wait(&ctx->fdmon_io_uring, wait_nr);
+    } while (ret == -EINTR);
+
     assert(ret >= 0);
 
     return process_cq_ring(ctx, ready_list);