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, 1 insertions, 2 deletions

diff --git a/block/mirror.c b/block/mirror.c
index 153758ca9f..e76e754d26 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -390,7 +390,6 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
         int io_sectors;
         unsigned int io_bytes;
         int64_t io_bytes_acct;
-        BlockDriverState *file;
         enum MirrorMethod {
             MIRROR_METHOD_COPY,
             MIRROR_METHOD_ZERO,
@@ -401,7 +400,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
         ret = bdrv_get_block_status_above(source, NULL,
                                           offset >> BDRV_SECTOR_BITS,
                                           nb_chunks * sectors_per_chunk,
-                                          &io_sectors, &file);
+                                          &io_sectors, NULL);
         io_bytes = io_sectors * BDRV_SECTOR_SIZE;
         if (ret < 0) {
             io_bytes = MIN(nb_chunks * s->granularity, max_io_bytes);