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[Qemu-devel] [PATCH v2 03/11] block: Add bdrv_has_zero_init_truncate()
From: |
Max Reitz |
Subject: |
[Qemu-devel] [PATCH v2 03/11] block: Add bdrv_has_zero_init_truncate() |
Date: |
Wed, 24 Jul 2019 19:12:31 +0200 |
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 <address@hidden>
---
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;
--
2.21.0
[Qemu-devel] [PATCH v2 04/11] block: Implement .bdrv_has_zero_init_truncate(), Max Reitz, 2019/07/24