Am 05.07.2012 18:37, schrieb Corey Bryant: >>>>> There is one case I'm aware of where we need to be careful: Before >>>>> opening an image, qemu may probe the format. In this case, the image >>>>> gets opened twice, and the first close comes before the second open. >>>>> I'm >>>>> not entirely sure how hard it would be to get rid of that behaviour. >>>>> >>>>> If we can't get rid of it, we have a small window that the refcount >>>>> doesn't really cover, and if we weren't careful it would become racy. >>>>> This is why I mentioned earlier that maybe we need to defer the >>>>> refcount >>>>> decrease a bit. However, I can't see how the in-use flag would make a >>>>> difference there. If the refcount can't cover it, the in-use flag can't >>>>> either. >>>> >>>> Yeah this is a problem. Could we introduce another flag to cover this? >>> >>> Adding more refcounts or flags is not a problem, but it doesn't solve it >>> either. The hard question is when to set that flag. >>> >>> I believe it may be easier to just change the block layer so that it >>> opens files only once during bdrv_open(). > > Can this fix be delivered after the fd passing patch series?
Sure, we can't fix everything at once. Kevin
