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