On 26.07.19 11:04, Stefano Garzarella wrote: > On Wed, Jul 24, 2019 at 07:12:31PM +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 <[email protected]> >> --- >> 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. >> */ > > Does it make sense to make sure of that in the bdrv_has_zero_init()? > > I mean something like this: > > int bdrv_has_zero_init(BlockDriverState *bs) > { > ... > if (bs->drv->bdrv_has_zero_init && bs->drv->bdrv_has_zero_init_truncate) { > return bs->drv->bdrv_has_zero_init_truncate(bs) && > bs->drv->bdrv_has_zero_init(bs); > } else if (bs->drv->bdrv_has_zero_init) > return bs->drv->bdrv_has_zero_init(bs); > } > ... > }
I thought about it, but I didn’t like it because that would mean that
bdrv_has_zero_init() kind of differs from .bdrv_has_zero_init().
Max
> Thanks,
> Stefano
>
>> 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;
>> --
>> 2.21.0
>>
>
signature.asc
Description: OpenPGP digital signature
