[Qemu-devel] [RFC 2/5] aio: Add io_read_poll() callback

[Max Reitz]

Similar to how qemu_set_fd_handler2() allows defining a function which
checks whether the recipient is ready to read, add aio_set_fd_handler2()
with a parameter for defining such a callback.

Signed-off-by: Max Reitz <address@hidden>
---
 aio-posix.c              | 26 ++++++++++++++++++++------
 include/block/aio.h      | 12 ++++++++++++
 include/qemu/main-loop.h |  1 -
 3 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/aio-posix.c b/aio-posix.c
index f921d4f..267df35 100644
--- a/aio-posix.c
+++ b/aio-posix.c
@@ -21,6 +21,7 @@
 struct AioHandler
 {
     GPollFD pfd;
+    IOCanReadHandler *io_read_poll;
     IOHandler *io_read;
     IOHandler *io_write;
     int deleted;
@@ -42,11 +43,12 @@ static AioHandler *find_aio_handler(AioContext *ctx, int fd)
     return NULL;
 }
 
-void aio_set_fd_handler(AioContext *ctx,
-                        int fd,
-                        IOHandler *io_read,
-                        IOHandler *io_write,
-                        void *opaque)
+void aio_set_fd_handler2(AioContext *ctx,
+                         int fd,
+                         IOCanReadHandler *io_read_poll,
+                         IOHandler *io_read,
+                         IOHandler *io_write,
+                         void *opaque)
 {
     AioHandler *node;
 
@@ -80,6 +82,7 @@ void aio_set_fd_handler(AioContext *ctx,
             g_source_add_poll(&ctx->source, &node->pfd);
         }
         /* Update handler with latest information */
+        node->io_read_poll = io_read_poll;
         node->io_read = io_read;
         node->io_write = io_write;
         node->opaque = opaque;
@@ -92,6 +95,15 @@ void aio_set_fd_handler(AioContext *ctx,
     aio_notify(ctx);
 }
 
+void aio_set_fd_handler(AioContext *ctx,
+                        int fd,
+                        IOHandler *io_read,
+                        IOHandler *io_write,
+                        void *opaque)
+{
+    aio_set_fd_handler2(ctx, fd, NULL, io_read, io_write, opaque);
+}
+
 void aio_set_event_notifier(AioContext *ctx,
                             EventNotifier *notifier,
                             EventNotifierHandler *io_read)
@@ -108,7 +120,9 @@ bool aio_pending(AioContext *ctx)
         int revents;
 
         revents = node->pfd.revents & node->pfd.events;
-        if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
+        if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read &&
+            (!node->io_read_poll || node->io_read_poll(node->opaque)))
+        {
             return true;
         }
         if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
diff --git a/include/block/aio.h b/include/block/aio.h
index a92511b..0a0ca14 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -44,6 +44,7 @@ void qemu_aio_release(void *p);
 typedef struct AioHandler AioHandler;
 typedef void QEMUBHFunc(void *opaque);
 typedef void IOHandler(void *opaque);
+typedef int IOCanReadHandler(void *opaque);
 
 struct AioContext {
     GSource source;
@@ -230,6 +231,17 @@ void aio_set_fd_handler(AioContext *ctx,
                         IOHandler *io_read,
                         IOHandler *io_write,
                         void *opaque);
+
+/* Similar to aio_set_fd_handler(), only that this form additionally allows
+ * registering an IOCanReadHandler which can be used for temporarily inhibiting
+ * io_read() from being called.
+ */
+void aio_set_fd_handler2(AioContext *ctx,
+                         int fd,
+                         IOCanReadHandler *io_read_poll,
+                         IOHandler *io_read,
+                         IOHandler *io_write,
+                         void *opaque);
 #endif
 
 /* Register an event notifier and associated callbacks.  Behaves very similarly
diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
index 6f0200a..01273f6 100644
--- a/include/qemu/main-loop.h
+++ b/include/qemu/main-loop.h
@@ -169,7 +169,6 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc 
*func, void *opaque);
 /* async I/O support */
 
 typedef void IOReadHandler(void *opaque, const uint8_t *buf, int size);
-typedef int IOCanReadHandler(void *opaque);
 
 /**
  * qemu_set_fd_handler2: Register a file descriptor with the main loop
-- 
1.9.3