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Stefan Hajnoczi authored
If a block driver has no file descriptors to monitor but there are still active requests, it can return 1 from .io_flush(). This is used to spin during synchronous I/O. Stop relying on .io_flush() and instead check QLIST_EMPTY(&bs->tracked_requests) to decide whether there are active requests. This is the first step in removing .io_flush() so that event loops no longer need to have the concept of synchronous I/O. Eventually we may be able to kill synchronous I/O completely by running everything in a coroutine, but that is future work. Note this patch moves bs->throttled_reqs initialization to bdrv_new() so that bdrv_requests_pending(bs) can safely access it. In practice bs is g_malloc0() so the memory is already zeroed but it's safer to initialize the queue properly. We also need to fix up block/stream.c:close_unused_images() to prevent traversing a dangling pointer while it rearranges the backing file chain. This is necessary since the new bdrv_drain_all() traverses the backing file chain. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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