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authorMax Reitz <mreitz@redhat.com>2019-07-24 19:12:31 +0200
committerMax Reitz <mreitz@redhat.com>2019-08-19 17:13:26 +0200
commitceaca56feee6a1d682c882300855cad44a67ec8e (patch)
tree28fe6b35daa9996adbc486fe57b7c606ff602fdc /block.c
parentcdf3bc934ad1e5319b03f2c85f381f5ffd2f8ca8 (diff)
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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>
Diffstat (limited to 'block.c')
-rw-r--r--block.c21
1 files changed, 21 insertions, 0 deletions
diff --git a/block.c b/block.c
index 3e698e9..874a29a 100644
--- a/block.c
+++ b/block.c
@@ -5078,6 +5078,27 @@ 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;