[Qemu-devel] mirror questions

[Vladimir Sementsov-Ogievskiy]

Hi!

A question about s->cow_bitmap, introduced in far b812f6719c
     "mirror: perform COW if the cluster size is bigger than the granularity"

cow_bitmap is just a bitmap which tracks, what clusters of target are 
allocated, to
prevent COW in target, if target backing is not ready yet. And it is done by 
just
aligning request to be larget and cover unaligned border clusters.

so, questions:

1. Is it correct that we align only on COPY operation in mirror_co_read? 
Misaligned
write_zero can also lead to COW, I think? Discard seems safe in this way, is it?

2. I don't see, how is it handled, if we align operation so that offset is 
decreases,
then it may intersect with previous mirror operation request, which may be not 
yet finished?

-- 
Best regards,
Vladimir