aio-posix: extract ppoll(2) and epoll(7) fd monitoring

The ppoll(2) and epoll(7) file descriptor monitoring implementations are
mixed with the core util/aio-posix.c code.  Before adding another
implementation for Linux io_uring, extract out the existing
ones so there is a clear interface and the core code is simpler.

The new interface is AioContext->fdmon_ops, a pointer to a FDMonOps
struct.  See the patch for details.

Semantic changes:
1. ppoll(2) now reflects events from pollfds[] back into AioHandlers
   while we're still on the clock for adaptive polling.  This was
   already happening for epoll(7), so if it's really an issue then we'll
   need to fix both in the future.
2. epoll(7)'s fallback to ppoll(2) while external events are disabled
   was broken when the number of fds exceeded the epoll(7) upgrade
   threshold.  I guess this code path simply wasn't tested and no one
   noticed the bug.  I didn't go out of my way to fix it but the correct
   code is simpler than preserving the bug.

I also took some liberties in removing the unnecessary
AioContext->epoll_available (just check AioContext->epollfd != -1
instead) and AioContext->epoll_enabled (it's implicit if our
AioContext->fdmon_ops callbacks are being invoked) fields.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20200305170806.1313245-4-stefanha@redhat.com
Message-Id: <20200305170806.1313245-4-stefanha@redhat.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/util/aio-posix.h b/util/aio-posix.h
new file mode 100644
index 0000000000..97899d0fbc
--- /dev/null
+++ b/util/aio-posix.h
@@ -0,0 +1,61 @@
+/*
+ * AioContext POSIX event loop implementation internal APIs
+ *
+ * Copyright IBM, Corp. 2008
+ * Copyright Red Hat, Inc. 2020
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ * Contributions after 2012-01-13 are licensed under the terms of the
+ * GNU GPL, version 2 or (at your option) any later version.
+ */
+
+#ifndef AIO_POSIX_H
+#define AIO_POSIX_H
+
+#include "block/aio.h"
+
+struct AioHandler {
+    GPollFD pfd;
+    IOHandler *io_read;
+    IOHandler *io_write;
+    AioPollFn *io_poll;
+    IOHandler *io_poll_begin;
+    IOHandler *io_poll_end;
+    void *opaque;
+    bool is_external;
+    QLIST_ENTRY(AioHandler) node;
+    QLIST_ENTRY(AioHandler) node_ready; /* only used during aio_poll() */
+    QLIST_ENTRY(AioHandler) node_deleted;
+};
+
+/* Add a handler to a ready list */
+void aio_add_ready_handler(AioHandlerList *ready_list, AioHandler *node,
+                           int revents);
+
+extern const FDMonOps fdmon_poll_ops;
+
+#ifdef CONFIG_EPOLL_CREATE1
+bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd);
+void fdmon_epoll_setup(AioContext *ctx);
+void fdmon_epoll_disable(AioContext *ctx);
+#else
+static inline bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
+{
+    return false;
+}
+
+static inline void fdmon_epoll_setup(AioContext *ctx)
+{
+}
+
+static inline void fdmon_epoll_disable(AioContext *ctx)
+{
+}
+#endif /* !CONFIG_EPOLL_CREATE1 */
+
+#endif /* AIO_POSIX_H */