@@ -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);
@@ -2810,6 +2810,10 @@ 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);
}
@@ -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,
@@ -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 the 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