[v2,19/20] block: Minimize raw use of bds->total_sectors

Commit Message

Eric Blake May 11, 2017, 2:20 a.m. UTC

bdrv_is_allocated_above() was relying on intermediate->total_sectors,
which is a field that can have stale contents depending on the value
of intermediate->has_variable_length.  An audit shows that we are safe
(we were first calling through bdrv_co_get_block_status() which in
turn calls bdrv_nb_sectors() and therefore just refreshed the current
length), but it's nicer to favor our accessor functions to avoid having
to repeat such an audit, even if it means refresh_total_sectors() is
called more frequently.

Suggested-by: John Snow <[e-mail]>
Signed-off-by: Eric Blake <[e-mail]>

---
v2: new patch
---
 block/io.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

Patch

diff --git a/block/io.c b/block/io.c
index 9ab89cb..20d3ebd 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1939,6 +1939,7 @@  int bdrv_is_allocated_above(BlockDriverState *top,
     intermediate = top;
     while (intermediate && intermediate != base) {
         int64_t pnum_inter;
+        int64_t size_inter;
         int psectors_inter;

         ret = bdrv_is_allocated(intermediate, sector_num * BDRV_SECTOR_SIZE,
@@ -1956,13 +1957,14 @@  int bdrv_is_allocated_above(BlockDriverState *top,

         /*
          * [sector_num, nb_sectors] is unallocated on top but intermediate
-         * might have
-         *
-         * [sector_num+x, nr_sectors] allocated.
+         * might have [sector_num+x, nb_sectors-x] allocated.
          */
+        size_inter = bdrv_nb_sectors(intermediate);
+        if (size_inter < 0) {
+            return size_inter;
+        }
         if (n > psectors_inter &&
-            (intermediate == top ||
-             sector_num + psectors_inter < intermediate->total_sectors)) {
+            (intermediate == top || sector_num + psectors_inter < size_inter)) {
             n = psectors_inter;
         }