Re: [Qemu-devel] [RFC PATCH] drive-backup 'stream' mode

[Wolfgang Richter]

On Sat, Oct 12, 2013 at 1:47 AM, Fam Zheng <address@hidden> wrote:
> While mirroring write is a good idea, doing it with drive-backup is probably
> not. The function of this command is to 'backup' the image with existing data,
> instead of new data. With your 'stream' mode, this semantic is changed.

I'm not so sure.  I think that it would be better to switch between
semantics with 'modes' rather than 'commands' to reduce documentation,
duplicate code, and burden on users to remember different commands.

Thus, many of the _modes_ of 'drive-backup' might provide you with
point-in-time snapshots of a block device, but some of them might just
mirror writes for backup purposes other than a point-in-time snapshot.

> IMO this feature is best implemented as a block filter, which is currently
> being discussed and not ready yet. A second option may be doing with another
> command (e.g. block-mirror, or a new one?)

That may be true, as I haven't followed block filters very closely
yet, but it seemed simple enough with the nice drive-backup code to
easily implement.

Perhaps this 'mode' could be refactored in the future to use block filters.

-- 
Wolf