[libvirt] storage volume download/upload

[Michal Privoznik]

On 05.05.2015 15:18, Vasiliy Tolstov wrote:
> As i see in some cases, for example in case of lvm storage pool
> libvirt spawns libvirt_iohelper to upload or download data to volume.
> But in case of big data contains zeroes this is wast bw of network.
> May be we can use gzip or lz4 for compression stream?
> How the best do this not breaking exiting software?
> May be add new parameter to libvirt_iohelper with compression method
> and compression level? In my cases of 20-160 Gb data and used only 4-5
> Gb this provide major benefit....
> Thanks!
> 

The main benefit of using iohelper is that we have aligned reads from
disks and thus can use O_DIRECT flag. So if anything, any compression
must be put in between iohelper and the daemon which then resends data
to clients.
Unfortunately, we don't have a field in the API signature that can be
used to select desired algorithm. We have @flags which could be used to
enable compression. Which algorithm to use can be set in a config file
(libvirtd.conf seems most suitable).

Michal