ssh: support I/O from any AioContext

The coroutine may run in a different AioContext, causing the
fd handler to busy wait.  Fix this by resetting the handler
in restart_coroutine, before the coroutine is restarted.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20170629132749.997-12-pbonzini@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>

block/ssh.c

@@ -888,13 +888,22 @@ static int ssh_has_zero_init(BlockDriverState *bs)
     return has_zero_init;
 }
 
+typedef struct BDRVSSHRestart {
+    BlockDriverState *bs;
+    Coroutine *co;
+} BDRVSSHRestart;
+
 static void restart_coroutine(void *opaque)
 {
-    Coroutine *co = opaque;
+    BDRVSSHRestart *restart = opaque;
+    BlockDriverState *bs = restart->bs;
+    BDRVSSHState *s = bs->opaque;
+    AioContext *ctx = bdrv_get_aio_context(bs);
 
-    DPRINTF("co=%p", co);
+    DPRINTF("co=%p", restart->co);
+    aio_set_fd_handler(ctx, s->sock, false, NULL, NULL, NULL, NULL);
 
-    aio_co_wake(co);
+    aio_co_wake(restart->co);
 }
 
 /* A non-blocking call returned EAGAIN, so yield, ensuring the
@@ -905,7 +914,10 @@ static coroutine_fn void co_yield(BDRVSSHState *s, BlockDriverState *bs)
 {
     int r;
     IOHandler *rd_handler = NULL, *wr_handler = NULL;
-    Coroutine *co = qemu_coroutine_self();
+    BDRVSSHRestart restart = {
+        .bs = bs,
+        .co = qemu_coroutine_self()
+    };
 
     r = libssh2_session_block_directions(s->session);
 
@@ -920,11 +932,9 @@ static coroutine_fn void co_yield(BDRVSSHState *s, BlockDriverState *bs)
             rd_handler, wr_handler);
 
     aio_set_fd_handler(bdrv_get_aio_context(bs), s->sock,
-                       false, rd_handler, wr_handler, NULL, co);
+                       false, rd_handler, wr_handler, NULL, &restart);
     qemu_coroutine_yield();
     DPRINTF("s->sock=%d - back", s->sock);
-    aio_set_fd_handler(bdrv_get_aio_context(bs), s->sock, false,
-                       NULL, NULL, NULL, NULL);
 }
 
 /* SFTP has a function `libssh2_sftp_seek64' which seeks to a position