Hi,
I've been playing with some code to implement an HTTP block device in
QEMU. I'll post when I've got something working. As I am building this
though, I thought of something that would be nice to have for qcow v2.
What I'd like is essentially a copy-on-read flag. If this flag is set,
and there is a base image, then whenever a read occurs to an unallocated
sector, the sector is copied from the base (similar to a write) and the
sector is allocated.
The idea is that copy-on-read is useful when read is really slow (for
instance, with an HTTP block device). This way, you could essentially
always use qcow + HTTP so that your block device was locally cached. It
seems a bit more elegant than trying to implement a caching mechanism in
the HTTP block device.
Regards,
Anthony Liguori
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