On 22.04.2014 17:19, Eric Blake wrote:
On 04/17/2014 03:59 PM, Max Reitz wrote:
After the top image has been committed into an image in its backing
chain, all images above that base image should be emptied to restore the
old qemu-img commit behavior.
Signed-off-by: Max Reitz <mre...@redhat.com>
---
qemu-img.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 84 insertions(+), 3 deletions(-)
Does emptying an image take significant time? If so, does that need to
be reflected in the progress meter?
For a 16 GB image I have here (should be nearly full) it took 1:22 min.
Copying it took six minutes, so I guess committing it would take even
more. I think the ratio is small enough not to include it in the
progress meter.
Furthermore, I don't see a reasonable implementation for a make_empty
progress output: As a general implementation for all image formats
implementing discard will not work (the qcow2 implementation clearly
states that discarded sectors should read back as zero), we would need
some way of returning the progress in every format-specific make_empty
implementation. This would probably require callbacks which I don't see
feasible.
An in my opinion more reasonable approach would be to speed up the
implementation of make_empty for qcow2 - as qcow does it, we could just
create a new empty image (that is, rewrite the L1 and refcount table and
truncate the image appropriately) instead of discarding every cluster in
the existing file. This would be much faster, but the implementation
would not be as nice and easy, so I chose not to implement it. I guess
I'll have a second look, then. ;-)
Max
