virtio: Add ability to detach unused buffers from vrings
There's currently no way for a virtio driver to ask for unused buffers, so it has to keep a list itself to reclaim them at shutdown. This is redundant, since virtio_ring stores that information. So add a new hook to do this. Signed-off-by: Shirley Ma <xma@us.ibm.com> Signed-off-by: Amit Shah <amit.shah@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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			@ -51,6 +51,9 @@ struct virtqueue {
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 *	This re-enables callbacks; it returns "false" if there are pending
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 *	buffers in the queue, to detect a possible race between the driver
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 *	checking for more work, and enabling callbacks.
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 * @detach_unused_buf: detach first unused buffer
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 * 	vq: the struct virtqueue we're talking about.
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 * 	Returns NULL or the "data" token handed to add_buf
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 *
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 * Locking rules are straightforward: the driver is responsible for
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 * locking.  No two operations may be invoked simultaneously, with the exception
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			@ -71,6 +74,7 @@ struct virtqueue_ops {
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	void (*disable_cb)(struct virtqueue *vq);
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	bool (*enable_cb)(struct virtqueue *vq);
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	void *(*detach_unused_buf)(struct virtqueue *vq);
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};
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/**
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