Am 20.11.2019 um 15:47 hat Vladimir Sementsov-Ogievskiy geschrieben: > 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. > > + */ > > Should we mention that, still, we don't care if user for some reason will > change > backing file in future?
This should be obvious, but I can add something. > > + 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); > > two over-80 lines Will fix. > > + if (ret < 0) { > > + goto out; > > + } > > + } > > + } > > should we improve "off" mode specification in qapi? I don't think we're changing the semantics of "off". We're merely fixing a bug that happens not to exist with preallocation. > > + > > ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS); > > if (ret < 0) { > > error_setg_errno(errp, -ret, "Could not refresh total sector > > count"); > > > > Hmm. is it correct to call write_zeroes before refresh_total_sectors? > Note that qcow2_co_pwrite_zeroes rely on bs->total_sectors... Hm... I placed the code where I did because I didn't want to make the new area valid before it isn't zeroed. But you're probably right that we shouldn't run requests with inconsistent bs->total_sectors, so I'll switch the order. Kevin