On 24/10/2019 12:34, Max Reitz wrote: > On 22.10.19 15:53, Andrey Shinkevich wrote: > > [...] > >> If the support of COW for compressed writes is found feasible, will it >> make a sense to implement? Then this series will follow. > > Hm, what exactly do you mean by support of COW for compressed writes? >
I spoke in terms of the commit message with the following ID: b0b6862e5e1a1394e0ab3d5da94ba8b0da8664e2 "qcow2: Fail write_compressed when overwriting data" "...qcow2_write_compressed() doesn't perform COW as it would have to do..." So, I suggest that we implement writing compressed data to the allocated clusters rather than qcow2_alloc_compressed_cluster_offset() returns the error. Particularly, when it comes to NBD server connection failure for writhing a compressed cluster, it may not be rewritten after the connection is restored. Are there any issues with that implementation idea? Andrey >> A comment for the option would warn a user that guest writing will work >> slower for if compress selected. > > I’m not sure whether that’s necessary. As a user, I would assume that > enabling compression will always make something slower. > > Max >