Am 25.09.2012 18:29, schrieb Jeff Cody:
> Add bdrv_find_overlay(), and bdrv_drop_intermediate().
>
> bdrv_find_overlay(): given 'bs' and the active (topmost) BDS of an image
> chain,
> find the image that is the immediate top of 'bs'
>
> bdrv_drop_intermediate():
> Given 3 BDS (active, top, base), drop images above
> base up to and including top, and set base to be the
> backing file of top's overlay node.
>
> E.g., this converts:
>
> bottom <- base <- intermediate <- top <- active
>
> to
>
> bottom <- base <- active
>
> Signed-off-by: Jeff Cody <jc...@redhat.com>
> +/*
> + * Drops images above 'base' up to and including 'top', and sets the image
> + * above 'top' to have base as its backing file.
> + *
> + * Requires that the overlay to 'top' is opened r/w, so that the backing file
> + * information in 'bs' can be properly updated.
> + *
> + * E.g., this will convert the following chain:
> + * bottom <- base <- intermediate <- top <- active
> + *
> + * to
> + *
> + * bottom <- base <- active
> + *
> + * It is allowed for bottom==base, in which case it converts:
> + *
> + * base <- intermediate <- top <- active
> + *
> + * to
> + *
> + * base <- active
Compared to RFC v2 you deleted this part of the comment:
+ *
+ * It is also allowed for top==active, except in that case active is not
+ * deleted:
You describe the condition now as an error (which I think is what our
conclusion on IRC was), but now I think the following example must be
removed as well:
> + *
> + * base <- intermediate <- top
> + *
> + * becomes
> + *
> + * base <- top
> + *
> + * Error conditions:
> + * if active == top, that is considered an error
> + *
> + */
> +int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
> + BlockDriverState *base)
> +{
> + BlockDriverState *intermediate;
> + BlockDriverState *base_bs = NULL;
> + BlockDriverState *new_top_bs = NULL;
> + BlkIntermediateStates *intermediate_state, *next;
> + int ret = -EIO;
> +
> + QSIMPLEQ_HEAD(states_to_delete, BlkIntermediateStates) states_to_delete;
> + QSIMPLEQ_INIT(&states_to_delete);
> +
> + if (!top->drv || !base->drv) {
> + goto exit;
> + }
> +
> + new_top_bs = bdrv_find_overlay(active, top);
> +
> + if (new_top_bs == NULL) {
> + /* we could not find the image above 'top', this is an error */
> + goto exit;
> + }
> +
> + /* special case of new_top_bs->backing_hd already pointing to base -
> nothing
> + * to do, no intermediate images */
> + if (new_top_bs->backing_hd == base) {
> + ret = 0;
> + goto exit;
> + }
> +
> + intermediate = new_top_bs->backing_hd; /* this should be the same
> + as 'top' */
Should? Is it the same or not? If yes, you can write it as an assert();
it no, the comment is only confusing.
(In fact it's obvious enough that I'd just go with intermediate = top;
without any comment)
Kevin
