20.11.2019 17:03, Kevin Wolf wrote: > When extending the size of an image that has a backing file larger than > its old size, make sure that the backing file data doesn't become > visible in the guest, but the added area is properly zeroed out. > > The old behaviour made a difference in 'block_resize' (where showing the > backing file data from an old snapshot rather than zeros is > questionable) as well as in commit block jobs (both from active and > intermediate nodes) and HMP 'commit', where committing to a short > backing file would incorrectly omit writing zeroes for unallocated > blocks on the top layer after the EOF of the short backing file. > > Signed-off-by: Kevin Wolf <kw...@redhat.com> > --- > block/io.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/block/io.c b/block/io.c > index 003f4ea38c..8683f7a4bd 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -3382,6 +3382,31 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, > int64_t offset, bool exact, > goto out; > } > > + /* > + * If the image has a backing file that is large enough that it would > + * provide data for the new area, we cannot leave it unallocated because > + * then the backing file content would become visible. Instead, zero-fill > + * the area where backing file and new area overlap. > + */ > + if (new_bytes && bs->backing && prealloc == PREALLOC_MODE_OFF) { > + int64_t backing_len; > + > + backing_len = bdrv_getlength(backing_bs(bs)); > + if (backing_len < 0) { > + ret = backing_len; > + goto out; > + } > + > + if (backing_len > old_size) { > + ret = bdrv_co_do_pwrite_zeroes(bs, old_size, > + MIN(new_bytes, backing_len - > old_size), > + BDRV_REQ_ZERO_WRITE | > BDRV_REQ_MAY_UNMAP); > + if (ret < 0) { > + goto out; > + } > + } > + } > + > ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS); > if (ret < 0) { > error_setg_errno(errp, -ret, "Could not refresh total sector > count"); >
Hmmmm. I'm think that for commit, we also should zero truncated area if !bdrv_has_zero_init_truncate(bs). But we should not do it here, as it should not be done if we just resizing disk.. What formats are that bad? -- Best regards, Vladimir