diff --git a/block/io.c b/block/io.c index 54f0968aee..a718d50ca2 100644 --- a/block/io.c +++ b/block/io.c @@ -2350,34 +2350,74 @@ bdrv_co_common_block_status_above(BlockDriverState *bs, int64_t *map, BlockDriverState **file) { + int ret; BlockDriverState *p; - int ret = 0; - bool first = true; + int64_t eof = 0; assert(bs != base); - for (p = bs; p != base; p = bdrv_filter_or_cow_bs(p)) { + + ret = bdrv_co_block_status(bs, want_zero, offset, bytes, pnum, map, file); + if (ret < 0 || *pnum == 0 || ret & BDRV_BLOCK_ALLOCATED) { + return ret; + } + + if (ret & BDRV_BLOCK_EOF) { + eof = offset + *pnum; + } + + assert(*pnum <= bytes); + bytes = *pnum; + + for (p = bdrv_filter_or_cow_bs(bs); p != base; + p = bdrv_filter_or_cow_bs(p)) + { ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map, file); if (ret < 0) { - break; + return ret; } - if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first) { + if (*pnum == 0) { /* - * Reading beyond the end of the file continues to read - * zeroes, but we can only widen the result to the - * unallocated length we learned from an earlier - * iteration. + * The top layer deferred to this layer, and because this layer is + * short, any zeroes that we synthesize beyond EOF behave as if they + * were allocated at this layer. + * + * We don't include BDRV_BLOCK_EOF into ret, as upper layer may be + * larger. We'll add BDRV_BLOCK_EOF if needed at function end, see + * below. */ + assert(ret & BDRV_BLOCK_EOF); *pnum = bytes; - } - if (ret & (BDRV_BLOCK_ZERO | BDRV_BLOCK_DATA)) { + if (file) { + *file = p; + } + ret = BDRV_BLOCK_ZERO | BDRV_BLOCK_ALLOCATED; break; } - /* [offset, pnum] unallocated on this layer, which could be only - * the first part of [offset, bytes]. */ - bytes = MIN(bytes, *pnum); - first = false; + if (ret & BDRV_BLOCK_ALLOCATED) { + /* + * We've found the node and the status, we must break. + * + * Drop BDRV_BLOCK_EOF, as it's not for upper layer, which may be + * larger. We'll add BDRV_BLOCK_EOF if needed at function end, see + * below. + */ + ret &= ~BDRV_BLOCK_EOF; + break; + } + + /* + * OK, [offset, offset + *pnum) region is unallocated on this layer, + * let's continue the diving. + */ + assert(*pnum <= bytes); + bytes = *pnum; } + + if (offset + *pnum == eof) { + ret |= BDRV_BLOCK_EOF; + } + return ret; } diff --git a/block/qcow2.c b/block/qcow2.c index b05512718c..b6cb4db8bb 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -3860,8 +3860,20 @@ static bool is_zero(BlockDriverState *bs, int64_t offset, int64_t bytes) if (!bytes) { return true; } - res = bdrv_block_status_above(bs, NULL, offset, bytes, &nr, NULL, NULL); - return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == bytes; + + /* + * bdrv_block_status_above doesn't merge different types of zeros, for + * example, zeros which come from the region which is unallocated in + * the whole backing chain, and zeros which come because of a short + * backing file. So, we need a loop. + */ + do { + res = bdrv_block_status_above(bs, NULL, offset, bytes, &nr, NULL, NULL); + offset += nr; + bytes -= nr; + } while (res >= 0 && (res & BDRV_BLOCK_ZERO) && nr && bytes); + + return res >= 0 && (res & BDRV_BLOCK_ZERO) && bytes == 0; } static coroutine_fn int qcow2_co_pwrite_zeroes(BlockDriverState *bs,