Signed-off-by: Peter Lieven <p...@kamp.de>
---
block-migration.c | 3 ++-
block.c | 4 ++++
block/backup.c | 2 +-
include/block/block.h | 7 +++++++
4 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/block-migration.c b/block-migration.c
index 713a8e3..fc4ef93 100644
--- a/block-migration.c
+++ b/block-migration.c
@@ -780,7 +780,8 @@ static int block_load(QEMUFile *f, void *opaque, int
version_id)
}
if (flags & BLK_MIG_FLAG_ZERO_BLOCK) {
- ret = bdrv_write_zeroes(bs, addr, nr_sectors, 0);
+ ret = bdrv_write_zeroes(bs, addr, nr_sectors,
+ BDRV_REQ_MAY_UNMAP);
} else {
buf = g_malloc(BLOCK_SIZE);
qemu_get_buffer(f, buf, BLOCK_SIZE);
diff --git a/block.c b/block.c
index e5918a7..6f498fc 100644
--- a/block.c
+++ b/block.c
@@ -2761,6 +2761,10 @@ int coroutine_fn bdrv_co_write_zeroes(BlockDriverState
*bs,
{
trace_bdrv_co_write_zeroes(bs, sector_num, nb_sectors);
+ if (!(bs->open_flags & BDRV_O_UNMAP)) {
+ flags &= ~BDRV_REQ_MAY_UNMAP;
+ }
+
return bdrv_co_do_writev(bs, sector_num, nb_sectors, NULL,
BDRV_REQ_ZERO_WRITE | flags);
}
diff --git a/block/backup.c b/block/backup.c
index 5f6a642..1ab080d 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -139,7 +139,7 @@ static int coroutine_fn backup_do_cow(BlockDriverState *bs,
if (buffer_is_zero(iov.iov_base, iov.iov_len)) {
ret = bdrv_co_write_zeroes(job->target,
start * BACKUP_SECTORS_PER_CLUSTER,
- n, 0);
+ n, BDRV_REQ_MAY_UNMAP);
} else {
ret = bdrv_co_writev(job->target,
start * BACKUP_SECTORS_PER_CLUSTER, n,
diff --git a/include/block/block.h b/include/block/block.h
index ddb6870..0328234 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -65,6 +65,13 @@ typedef struct BlockDevOps {
typedef enum {
BDRV_REQ_COPY_ON_READ = 0x1,
BDRV_REQ_ZERO_WRITE = 0x2,
+ /* the BDRV_REQ_MAY_UNMAP flag is used to indicate that block driver
+ * is allowed to optimize a write zeroes request by unmapping (discarding)
+ * blocks if it is guaranteed that the result will read back as
+ * zeroes. the flag is only passed to the driver if the block device is
+ * opened with BDRV_O_UNMAP.
+ */
+ BDRV_REQ_MAY_UNMAP = 0x4,
} BdrvRequestFlags;
#define BDRV_O_RDWR 0x0002
--
1.7.9.5
