[PATCH] qapi: deprecate drive-backup
Kashyap Chamarthy
kchamart at redhat.com
Tue Apr 27 12:16:47 UTC 2021
On Mon, Apr 26, 2021 at 01:34:17PM -0400, John Snow wrote:
> On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
> > Modern way is using blockdev-add + blockdev-backup, which provides a
> > lot more control on how target is opened.
[...]
> 1) Let's add a sphinx reference to
> https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup
>
>
> 2) Just a thought, not a request: We also may wish to update
> https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the
> new, preferred method. However, this doc is a bit old and is in need
> of an overhaul anyway (Especially to add the NBD pull workflow.) Since
> the doc is in need of an overhaul anyway, can we ask Kashyap to help
> us here, if he has time?
Yes, I should be able to make time and help here; been putting it off on
the back burner. Thanks for the reminder. :) I'd like to update both
these:
https://qemu-project.gitlab.io/qemu/interop/bitmaps.html
https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html
Both of them, as you know, refer to 'drive-backup'. They also need
other adjustments / additions. Also perhaps break the larger doc into a
couple of smaller ones.
I'll start working on it the end of this week. First I need to tinker
with some of the recent improvements to refresh my memory and get a
sense of the modifications involved. So please bear with me.
> 3) Let's add a small explanation here that outlines the differences in
> using these two commands. Here's a suggestion:
>
> This change primarily separates the creation/opening process of the
> backup target with explicit, separate steps. BlockdevBackup uses
> mostly the same arguments as DriveBackup, except the "format" and
> "mode" options are removed in favor of using explicit
> "blockdev-create" and "blockdev-add" calls.
>
> The "target" argument changes semantics. It no longer accepts
> filenames, and will now additionally accept arbitrary node names in
> addition to device names.
Yeah; this is something I had figure out by some trial-and-error when I
was playing with it in the past.
> 4) Also not a request: If we want to go above and beyond, it might be nice
> to spell out the exact steps required to transition from the old interface
> to the new one. Here's a (hasty) suggestion for how that might look:
>
> - The MODE argument is deprecated.
> - "existing" is replaced by using "blockdev-add" commands.
> - "absolute-paths" is replaced by using "blockdev-add" and
> "blockdev-create" commands.
>
> - The FORMAT argument is deprecated.
> - Format information is given to "blockdev-add"/"blockdev-create".
>
> - The TARGET argument has new semantics:
> - Filenames are no longer supported, use blockdev-add/blockdev-create
> as necessary instead.
> - Device targets remain supported.
Agreed; docs like these can be useful for management tools that rely on
the old behaviour and are not as up-to-date as libvirt in keeping track
of QEMU developments.
[...]
--
/kashyap
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