block: Allow NULL file for bdrv_get_block_status()

Not all callers care about which BDS owns the mapping for a given
range of the file.  This patch merely simplifies the callers by
consolidating the logic in the common call point, while guaranteeing
a non-NULL file to all the driver callbacks, for no semantic change.
The only caller that does not care about pnum is bdrv_is_allocated,
as invoked by vvfat; we can likewise add assertions that the rest
of the stack does not have to worry about a NULL pnum.

Furthermore, this will also set the stage for a future cleanup: when
a caller does not care about which BDS owns an offset, it would be
nice to allow the driver to optimize things to not have to return
BDRV_BLOCK_OFFSET_VALID in the first place.  In the case of fragmented
allocation (for example, it's fairly easy to create a qcow2 image
where consecutive guest addresses are not at consecutive host
addresses), the current contract requires bdrv_get_block_status()
to clamp *pnum to the limit where host addresses are no longer
consecutive, but allowing a NULL file means that *pnum could be
set to the full length of known-allocated data.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 6 deletions

diff --git a/qemu-img.c b/qemu-img.c
index d6007b2a6d..e9c7b30c91 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1375,7 +1375,6 @@ static int img_compare(int argc, char **argv)
 
     for (;;) {
         int64_t status1, status2;
-        BlockDriverState *file;
 
         nb_sectors = sectors_to_process(total_sectors, sector_num);
         if (nb_sectors <= 0) {
@@ -1383,7 +1382,7 @@ static int img_compare(int argc, char **argv)
         }
         status1 = bdrv_get_block_status_above(bs1, NULL, sector_num,
                                               total_sectors1 - sector_num,
-                                              &pnum1, &file);
+                                              &pnum1, NULL);
         if (status1 < 0) {
             ret = 3;
             error_report("Sector allocation test failed for %s", filename1);
@@ -1393,7 +1392,7 @@ static int img_compare(int argc, char **argv)
 
         status2 = bdrv_get_block_status_above(bs2, NULL, sector_num,
                                               total_sectors2 - sector_num,
-                                              &pnum2, &file);
+                                              &pnum2, NULL);
         if (status2 < 0) {
             ret = 3;
             error_report("Sector allocation test failed for %s", filename2);
@@ -1599,15 +1598,14 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
     n = MIN(s->total_sectors - sector_num, BDRV_REQUEST_MAX_SECTORS);
 
     if (s->sector_next_status <= sector_num) {
-        BlockDriverState *file;
         if (s->target_has_backing) {
             ret = bdrv_get_block_status(blk_bs(s->src[src_cur]),
                                         sector_num - src_cur_offset,
-                                        n, &n, &file);
+                                        n, &n, NULL);
         } else {
             ret = bdrv_get_block_status_above(blk_bs(s->src[src_cur]), NULL,
                                               sector_num - src_cur_offset,
-                                              n, &n, &file);
+                                              n, &n, NULL);
         }
         if (ret < 0) {
             return ret;