Re: [Qemu-devel] [RFC PATCH 2/4] block: add live block commit functionality

[Jeff Cody <jcody@redhat.com>]

On 07/31/2012 01:51 PM, Eric Blake wrote:
> On 07/30/2012 11:16 PM, Jeff Cody wrote:
>> This adds the live commit coroutine.  This iteration focuses on the
>> commit only below the active layer, and not the active layer itself.
>>
>> The behaviour is similar to block streaming; the sectors are walked
>> through, and anything that exists above 'base' is committed back down
>> into base.  At the end, intermediate images are deleted, and the
>> chain stiched together.  Images are restored to their original open
> 
> s/stiched/stitched/
> 
>> +
>> +enum {
>> +    /*
>> +     * Size of data buffer for populating the image file.  This should be large
>> +     * enough to process multiple clusters in a single call, so that populating
>> +     * contiguous regions of the image is efficient.
>> +     */
>> +    COMMIT_BUFFER_SIZE = 512 * 1024, /* in bytes */
>> +};
> 
> Paolo's latest round of patches got to the point of making this
> configurable for drive-mirror; is that something you should be copying here?

Yes

> 
>> +++ b/block_int.h
>> @@ -342,4 +342,23 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
>>                    BlockDriverCompletionFunc *cb,
>>                    void *opaque, Error **errp);
>>  
>> +/**
>> + * commit_start:
>> + * @bs: Top Block device
>> + * @base: Block device that will be written into, and become the new top
>> + * @speed: The maximum speed, in bytes per second, or 0 for unlimited.
>> + * @on_error: The action to take upon error.
> 
> Do we need to distinguish between rerror and werror?

Good question - I don't think that would change the error handling, but
it may be useful information to get the user.  If you prefer rerror and
werror distinction, I'll add that in.

> 
>> + * @cb: Completion function for the job.
>> + * @opaque: Opaque pointer value passed to @cb.
>> + * @orig_base_flags: The original open flags for the base image
>> + * @orig_top_flags: The original open flags for the top image
>> + * @errp: Error object.
>> + *
>> + */
>> +void commit_start(BlockDriverState *bs, BlockDriverState *base,
>> +                 BlockDriverState *top, int64_t speed,
>> +                 BlockdevOnError on_error, BlockDriverCompletionFunc *cb,
>> +                 void *opaque, int orig_base_flags, int orig_top_flags,
>> +                 Error **errp);
>> +
>>  #endif /* BLOCK_INT_H */
>