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Re: [Qemu-devel] [PATCH 33/47] mirror: add support for on-source-error/o

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH 33/47] mirror: add support for on-source-error/on-target-error
Date: Fri, 27 Jul 2012 09:26:57 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0

On 07/24/2012 05:04 AM, Paolo Bonzini wrote:
> Error management is important for mirroring; otherwise, an error on the
> target (even something as "innocent" as ENOSPC) requires to start again
> with a full copy.  Similar to on_read_error/on_write_error, two separate
> knobs are provided for on_source_error (reads) and on_target_error (writes).
> The default is 'report' for both.
> The 'ignore' policy will leave the sector dirty, so that it will be
> retried later.  Thus, it will not cause corruption.

How frequently will the dirty sector be retried when the policy is
'ignore'?  Are we going to be causing a denial-of-service by repeatedly
retrying the sector until the user does something about the error event?

> +++ b/qapi-schema.json
> @@ -1389,17 +1389,27 @@
>  #        (all the disk, only the sectors allocated in the topmost image, or
>  #        only new I/O).
>  #
> +# @on-source-error: #optional the action to take on an error on the source,
> +#                   default 'report'.  'stop' and 'enospc' can only be used
> +#                   if the block device supports io-status (see BlockInfo).
> +#
> +# @on-target-error: #optional the action to take on an error on the target,
> +#                   default 'report' (no limitations, since this applies to
> +#                   a different block device than @device).
> +#
>  # Returns: nothing on success
>  #          If @device is not a valid block device, DeviceNotFound
>  #          If @target can't be opened, OpenFileFailed
>  #          If @format is invalid, InvalidBlockFormat
> +#          If @on_source_error is not supported, InvalidParameter


Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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