diff options
| -rw-r--r-- | qemu-img.c | 42 |
1 files changed, 33 insertions, 9 deletions
diff --git a/qemu-img.c b/qemu-img.c index 8bdae66490..01cc0d35ad 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1420,6 +1420,8 @@ static int img_rebase(int argc, char **argv) */ if (!unsafe) { uint64_t num_sectors; + uint64_t old_backing_num_sectors; + uint64_t new_backing_num_sectors; uint64_t sector; int n; uint8_t * buf_old; @@ -1430,6 +1432,8 @@ static int img_rebase(int argc, char **argv) buf_new = qemu_blockalign(bs, IO_BUF_SIZE); bdrv_get_geometry(bs, &num_sectors); + bdrv_get_geometry(bs_old_backing, &old_backing_num_sectors); + bdrv_get_geometry(bs_new_backing, &new_backing_num_sectors); local_progress = (float)100 / (num_sectors / MIN(num_sectors, IO_BUF_SIZE / 512)); @@ -1448,16 +1452,36 @@ static int img_rebase(int argc, char **argv) continue; } - /* Read old and new backing file */ - ret = bdrv_read(bs_old_backing, sector, buf_old, n); - if (ret < 0) { - error_report("error while reading from old backing file"); - goto out; + /* + * Read old and new backing file and take into consideration that + * backing files may be smaller than the COW image. + */ + if (sector >= old_backing_num_sectors) { + memset(buf_old, 0, n * BDRV_SECTOR_SIZE); + } else { + if (sector + n > old_backing_num_sectors) { + n = old_backing_num_sectors - sector; + } + + ret = bdrv_read(bs_old_backing, sector, buf_old, n); + if (ret < 0) { + error_report("error while reading from old backing file"); + goto out; + } } - ret = bdrv_read(bs_new_backing, sector, buf_new, n); - if (ret < 0) { - error_report("error while reading from new backing file"); - goto out; + + if (sector >= new_backing_num_sectors) { + memset(buf_new, 0, n * BDRV_SECTOR_SIZE); + } else { + if (sector + n > new_backing_num_sectors) { + n = new_backing_num_sectors - sector; + } + + ret = bdrv_read(bs_new_backing, sector, buf_new, n); + if (ret < 0) { + error_report("error while reading from new backing file"); + goto out; + } } /* If they differ, we need to write to the COW file */ |