On Wed, 07/24 19:16, Jeff Cody wrote:
> On Wed, Jul 17, 2013 at 05:42:13PM +0800, Fam Zheng wrote:
> > bdrv_drop_intermediate used a local list to iterate through backing
> > chain and delete each BDS. It is simplified while adopting to refcount
> > mechanism.
> >
>
> Hi Fam,
>
> The reason for the local list is to keep the BDS deletion
> transactional, so it can be rolled back in case of error (see below)
>
> > Signed-off-by: Fam Zheng <f...@redhat.com>
> > ---
> > block.c | 71
> > ++++++++++-------------------------------------------------------
> > 1 file changed, 11 insertions(+), 60 deletions(-)
> >
> > diff --git a/block.c b/block.c
> > index 57a3876..499de22 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -2027,12 +2027,6 @@ BlockDriverState *bdrv_find_overlay(BlockDriverState
> > *active,
> > return overlay;
> > }
> >
> > -typedef struct BlkIntermediateStates {
> > - BlockDriverState *bs;
> > - QSIMPLEQ_ENTRY(BlkIntermediateStates) entry;
> > -} BlkIntermediateStates;
> > -
> > -
> > /*
> > * Drops images above 'base' up to and including 'top', and sets the image
> > * above 'top' to have base as its backing file.
> > @@ -2062,15 +2056,9 @@ typedef struct BlkIntermediateStates {
> > 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;
> > }
> > @@ -2082,58 +2070,21 @@ int bdrv_drop_intermediate(BlockDriverState
> > *active, BlockDriverState *top,
> > 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 = top;
> > -
> > - /* now we will go down through the list, and add each BDS we find
> > - * into our deletion queue, until we hit the 'base'
> > - */
> > - while (intermediate) {
> > - intermediate_state = g_malloc0(sizeof(BlkIntermediateStates));
> > - intermediate_state->bs = intermediate;
> > - QSIMPLEQ_INSERT_TAIL(&states_to_delete, intermediate_state, entry);
> > -
> > - if (intermediate->backing_hd == base) {
> > - base_bs = intermediate->backing_hd;
> > - break;
> > + while (new_top_bs->backing_hd && new_top_bs->backing_hd != base) {
> > + BlockDriverState *backing = new_top_bs->backing_hd;
> > + if (backing == NULL) {
> > + goto exit;
>
> If you simplify it until just a while loop that unrefs/deletes the BDS
> inside the loop as you navigate the chain, then any error exit leaves
> you in a bad state, with a potentially invalid chain. This is one
> such error potential.
>
Yes, I'll fix this.
--
Fam
