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block: Add bdrv_has_zero_init_truncate()
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 <mreitz@redhat.com> Message-id: 20190724171239.8764-4-mreitz@redhat.com Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
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21
block.c
21
block.c
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@ -5078,6 +5078,27 @@ int bdrv_has_zero_init(BlockDriverState *bs)
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return 0;
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}
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int bdrv_has_zero_init_truncate(BlockDriverState *bs)
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{
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if (!bs->drv) {
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return 0;
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}
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if (bs->backing) {
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/* Depends on the backing image length, but better safe than sorry */
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return 0;
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}
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if (bs->drv->bdrv_has_zero_init_truncate) {
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return bs->drv->bdrv_has_zero_init_truncate(bs);
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}
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if (bs->file && bs->drv->is_filter) {
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return bdrv_has_zero_init_truncate(bs->file->bs);
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}
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/* safe default */
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return 0;
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}
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bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs)
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{
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BlockDriverInfo bdi;
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@ -443,6 +443,7 @@ int bdrv_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes);
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int bdrv_co_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes);
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int bdrv_has_zero_init_1(BlockDriverState *bs);
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int bdrv_has_zero_init(BlockDriverState *bs);
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int bdrv_has_zero_init_truncate(BlockDriverState *bs);
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bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs);
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bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs);
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int bdrv_block_status(BlockDriverState *bs, int64_t offset,
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@ -419,9 +419,16 @@ struct BlockDriver {
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/*
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* Returns 1 if newly created images are guaranteed to contain only
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* zeros, 0 otherwise.
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* Must return 0 if .bdrv_has_zero_init_truncate() returns 0.
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*/
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int (*bdrv_has_zero_init)(BlockDriverState *bs);
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/*
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* Returns 1 if new areas added by growing the image with
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* PREALLOC_MODE_OFF contain only zeros, 0 otherwise.
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*/
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int (*bdrv_has_zero_init_truncate)(BlockDriverState *bs);
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/* Remove fd handlers, timers, and other event loop callbacks so the event
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* loop is no longer in use. Called with no in-flight requests and in
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* depth-first traversal order with parents before child nodes.
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