Dropping intermediate could be useful both for commit and stream, and
BDS refcnt plus bdrv_swap could do most of the job nicely. It also needs
to work with op blockers.
Signed-off-by: Fam Zheng <f...@redhat.com>
---
block.c | 146 +++++++++++++++++++++++++--------------------------------
block/commit.c | 1 +
2 files changed, 66 insertions(+), 81 deletions(-)
diff --git a/block.c b/block.c
index be58d93..e51ead3 100644
--- a/block.c
+++ b/block.c
@@ -2468,115 +2468,99 @@ 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.
+ * Drops images above 'base' up to and including 'top', and sets new 'base'
+ * as backing_hd of top_overlay (the image orignally has 'top' as backing
+ * file). top_overlay may be NULL if 'top' is active, no such update needed.
+ * Requires that the top_overlay to 'top' is opened r/w.
*
- * Requires that the overlay to 'top' is opened r/w, so that the backing file
- * information in 'bs' can be properly updated.
+ * 1) This will convert the following chain:
*
- * E.g., this will convert the following chain:
- * bottom <- base <- intermediate <- top <- active
+ * ... <- base <- ... <- top <- overlay <-... <- active
*
* to
*
- * bottom <- base <- active
+ * ... <- base <- overlay <- active
*
- * It is allowed for bottom==base, in which case it converts:
+ * 2) It is allowed for bottom==base, in which case it converts:
*
- * base <- intermediate <- top <- active
+ * base <- ... <- top <- overlay <- ... <- active
*
* to
*
- * base <- active
+ * base <- overlay <- active
+ *
+ * 2) It also allows active==top, in which case it converts:
+ *
+ * ... <- base <- ... <- top (active)
+ *
+ * to
+ *
+ * ... <- base == active == top
+ *
+ * i.e. only base and lower remains: *top == *base when return.
+ *
+ * 3) If base==NULL, it will drop all the BDS below overlay and set its
+ * backing_hd to NULL. I.e.:
+ *
+ * base(NULL) <- ... <- overlay <- ... <- active
+ *
+ * to
*
- * Error conditions:
- * if active == top, that is considered an error
+ * overlay <- ... <- active
*
*/
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);
+ BlockDriverState *drop_start, *overlay;
+ int ret = -EINVAL;
- if (new_top_bs == NULL) {
- /* we could not find the image above 'top', this is an error */
+ if (!top->drv || (base && !base->drv)) {
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) {
+ if (top == 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;
+ } else if (top == active) {
+ assert(base);
+ drop_start = active->backing_hd;
+ bdrv_swap(active, base);
+ base->backing_hd = NULL;
+ bdrv_unref(drop_start);
+ ret = 0;
+ } else {
+ /* If there's an overlay, its backing_hd points to top's BDS now,
+ * the top image is dropped but this BDS structure is kept and swapped
+ * with base, this way we keep the pointers valid after dropping top */
+ overlay = bdrv_find_overlay(active, top);
+ if (!overlay) {
+ goto exit;
+ }
+ if (base) {
+ ret = bdrv_change_backing_file(overlay, base->filename,
+ base->drv->format_name);
+ } else {
+ ret = bdrv_change_backing_file(overlay, NULL, NULL);
+ }
+ if (ret) {
+ goto exit;
+ }
+ if (base) {
+ drop_start = top->backing_hd;
+ bdrv_swap(top, base);
+ /* Break the loop formed by bdrv_swap */
+ bdrv_set_backing_hd(base, NULL);
+ } else {
+ bdrv_set_backing_hd(overlay, NULL);
+ drop_start = top;
}
- intermediate = intermediate->backing_hd;
- }
- if (base_bs == NULL) {
- /* something went wrong, we did not end at the base. safely
- * unravel everything, and exit with error */
- goto exit;
- }
-
- /* success - we can delete the intermediate states, and link top->base */
- ret = bdrv_change_backing_file(new_top_bs, base_bs->filename,
- base_bs->drv ? base_bs->drv->format_name :
"");
- if (ret) {
- goto exit;
- }
- new_top_bs->backing_hd = base_bs;
-
- bdrv_refresh_limits(new_top_bs);
- QSIMPLEQ_FOREACH_SAFE(intermediate_state, &states_to_delete, entry, next) {
- /* so that bdrv_close() does not recursively close the chain */
- intermediate_state->bs->backing_hd = NULL;
- bdrv_unref(intermediate_state->bs);
+ bdrv_unref(drop_start);
}
- ret = 0;
-
exit:
- QSIMPLEQ_FOREACH_SAFE(intermediate_state, &states_to_delete, entry, next) {
- g_free(intermediate_state);
- }
return ret;
}
-
static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
size_t size)
{
diff --git a/block/commit.c b/block/commit.c
index acec4ac..b10eb79 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -142,6 +142,7 @@ wait:
if (!block_job_is_cancelled(&s->common) && sector_num == end) {
/* success */
ret = bdrv_drop_intermediate(active, top, base);
+ base = top;
}
exit_free_buf:
--
1.8.5.3
