[Qemu-devel] [PATCH v4 20/21] block: Minimize raw use of bds->total_sectors

[Eric Blake <eblake@redhat.com>]

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 <jsnow@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Manos Pitsidianakis <el13635@mail.ntua.gr>
Reviewed-by: Jeff Cody <jcody@redhat.com>

---
v3-v4: no change
v2: new patch
---
 block/io.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/io.c b/block/io.c
index cb40069..fb8d1c7 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1952,6 +1952,7 @@ 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,
@@ -1969,13 +1970,14 @@ 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;
         }

-- 
2.9.4