Am 05.07.2017 um 23:08 hat Eric Blake geschrieben: > 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 <js...@redhat.com> > Signed-off-by: Eric Blake <ebl...@redhat.com> > Reviewed-by: Manos Pitsidianakis <el13...@mail.ntua.gr> > Reviewed-by: Jeff Cody <jc...@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. > */
I tried to figure out what this comment wants to tell us, and neither the original version nor your changed one seemed to make a lot of sense to me. The only case that I can see that actually needs the following block is a case like this: (. = unallocated, # = allocated) top ....#### intermediate ........ Our initial request was for 8 sectors, but when going to the intermediate node, we need to reduce this to 4 sectors, otherwise we would return unallocated for sectors 5 to 8 even though they are allocated in top. That's kind of the opposite of what the comment says, though... > + 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; > } The actual code change looks good. Kevin