On Wed, 2019-07-24 at 19:12 +0200, Max Reitz wrote: > No .bdrv_has_zero_init() implementation returns 1 if growing the file > would add non-zero areas (at least with PREALLOC_MODE_OFF), so using it > in lieu of this new function was always safe. > > But on the other hand, it is possible that growing an image that is not > zero-initialized would still add a zero-initialized area, like when > using nonpreallocating truncation on a preallocated image. For callers > that care only about truncation, not about creation with potential > preallocation, this new function is useful. > > Alternatively, we could have added a PreallocMode parameter to > bdrv_has_zero_init(). But the only user would have been qemu-img > convert, which does not have a plain PreallocMode value right now -- it > would have to parse the creation option to obtain it. Therefore, the > simpler solution is to let bdrv_has_zero_init() inquire the > preallocation status and add the new bdrv_has_zero_init_truncate() that > presupposes PREALLOC_MODE_OFF. > > Signed-off-by: Max Reitz <mre...@redhat.com> > --- > include/block/block.h | 1 + > include/block/block_int.h | 7 +++++++ > block.c | 21 +++++++++++++++++++++ > 3 files changed, 29 insertions(+) > > diff --git a/include/block/block.h b/include/block/block.h > index 50a07c1c33..5321d8afdf 100644 > --- a/include/block/block.h > +++ b/include/block/block.h > @@ -438,6 +438,7 @@ int bdrv_pdiscard(BdrvChild *child, int64_t offset, > int64_t bytes); > int bdrv_co_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes); > int bdrv_has_zero_init_1(BlockDriverState *bs); > int bdrv_has_zero_init(BlockDriverState *bs); > +int bdrv_has_zero_init_truncate(BlockDriverState *bs); > bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs); > bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs); > int bdrv_block_status(BlockDriverState *bs, int64_t offset, > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 6a0b1b5008..d7fc6b296b 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -420,9 +420,16 @@ struct BlockDriver { > /* > * Returns 1 if newly created images are guaranteed to contain only > * zeros, 0 otherwise. > + * Must return 0 if .bdrv_has_zero_init_truncate() returns 0. > */ > int (*bdrv_has_zero_init)(BlockDriverState *bs); > > + /* > + * Returns 1 if new areas added by growing the image with > + * PREALLOC_MODE_OFF contain only zeros, 0 otherwise. > + */ > + int (*bdrv_has_zero_init_truncate)(BlockDriverState *bs); > + > /* Remove fd handlers, timers, and other event loop callbacks so the > event > * loop is no longer in use. Called with no in-flight requests and in > * depth-first traversal order with parents before child nodes. > diff --git a/block.c b/block.c > index cbd8da5f3b..81ae44dcf3 100644 > --- a/block.c > +++ b/block.c > @@ -5066,6 +5066,27 @@ int bdrv_has_zero_init(BlockDriverState *bs) > return 0; > } > > +int bdrv_has_zero_init_truncate(BlockDriverState *bs) > +{ > + if (!bs->drv) { > + return 0; > + } > + > + if (bs->backing) { > + /* Depends on the backing image length, but better safe than sorry */ > + return 0; > + } > + if (bs->drv->bdrv_has_zero_init_truncate) { > + return bs->drv->bdrv_has_zero_init_truncate(bs); > + } > + if (bs->file && bs->drv->is_filter) { > + return bdrv_has_zero_init_truncate(bs->file->bs); > + } > + > + /* safe default */ > + return 0; > +} > + > bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs) > { > BlockDriverInfo bdi;
This looks like a very correct change, even for the sake of clarifying the scope of bdrv_has_zero_init Reviewed-by: Maxim Levitsky <mlevi...@redhat.com> Best regards, Maxim Levitsky