Re: [libvirt] [Qemu-devel] [PATCH v4 0/7] file descriptor passing using pass-fd

>>>> 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?