Re: [Qemu-devel] [PATCH v2] migration: update docs

[Eric Blake]

On 04/27/2018 12:34 PM, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> Update the migration docs:
> 
> Among other changes:
>   * Added a general list of advice for device authors
>   * Reordered the section on conditional state (subsections etc)
>     into the order we prefer.
>   * Add a note about firmware
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  docs/devel/migration.rst | 531 +++++++++++++++++++++++++++------------
>  1 file changed, 375 insertions(+), 156 deletions(-)

> +
> +General advice for device developers
> +------------------------------------
> +
> +- The migration state saved should reflect the device being modelled rather
> +  than the way your implementation works.   That way if you change the 
> implementation

Three spaces between sentences is unusual.


> +
> +- The migration might happen at an inconvenient point,
> +  e.g. right in the middle of the guest reprogramming the device, during
> +  guest reboot or shutdown or while the device is waiting for external IO.
> +  It's strongly preferred that migrations do not fail in this situation,
> +  since in the cloud environment migrations might happen automatically to
> +  VMs that the administrator doesn't directly control.

Not for this patch, but is there any mechanism for a device to request
that migration be delayed just long enough for the device to have a
chance to get out of that inconsistent state, rather than having to
migrate the inconvenient state?

> +When we migrate a device, we save/load the state as a series
> +of fields.  Some times, due to bugs or new functionality, we need to

Sometimes


> @@ -328,9 +329,12 @@ Sometimes members of the VMState are no longer needed:
>  
>    - removing them will break migration compatibility
>  
> -  - making them version dependent and bumping the version will break 
> backwards migration compatibility.
> +  - making them version dependent and bumping the version will break 
> backward migration compatibility.

Is it worth worrying about long lines?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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