[Qemu-devel] [PATCHv4 04/17] block: introduce bdrv_has_discard_zeroes and bdrv_has_discard_write_zeroes

[Peter Lieven <pl@kamp.de>]

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
---
 block.c                   |   29 +++++++++++++++++++++++++++++
 include/block/block.h     |    2 ++
 include/block/block_int.h |   13 +++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/block.c b/block.c
index 0675257..6a46bc2 100644
--- a/block.c
+++ b/block.c
@@ -3085,6 +3085,35 @@ int bdrv_has_zero_init(BlockDriverState *bs)
     return 0;
 }
 
+bool bdrv_has_discard_zeroes(BlockDriverState *bs)
+{
+    assert(bs->drv);
+
+    if (bs->backing_hd) {
+        return false;
+    }
+    if (bs->drv->bdrv_has_discard_zeroes) {
+        return bs->drv->bdrv_has_discard_zeroes(bs);
+    }
+
+    return false;
+}
+
+bool bdrv_has_discard_write_zeroes(BlockDriverState *bs)
+{
+    assert(bs->drv);
+
+    if (bs->backing_hd || !(bs->open_flags & BDRV_O_UNMAP)) {
+        return false;
+    }
+
+    if (bs->drv->bdrv_has_discard_write_zeroes) {
+        return bs->drv->bdrv_has_discard_write_zeroes(bs);
+    }
+
+    return false;
+}
+
 typedef struct BdrvCoGetBlockStatusData {
     BlockDriverState *bs;
     BlockDriverState *base;
diff --git a/include/block/block.h b/include/block/block.h
index b72c81a..2de226f 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -310,6 +310,8 @@ int bdrv_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors);
 int bdrv_co_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors);
 int bdrv_has_zero_init_1(BlockDriverState *bs);
 int bdrv_has_zero_init(BlockDriverState *bs);
+bool bdrv_has_discard_zeroes(BlockDriverState *bs);
+bool bdrv_has_discard_write_zeroes(BlockDriverState *bs);
 int64_t bdrv_get_block_status(BlockDriverState *bs, int64_t sector_num,
                               int nb_sectors, int *pnum);
 int bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
diff --git a/include/block/block_int.h b/include/block/block_int.h
index f95dba7..ce5c62e 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -217,6 +217,19 @@ struct BlockDriver {
      */
     int (*bdrv_has_zero_init)(BlockDriverState *bs);
 
+    /*
+     * Returns true if discarded blocks read back as zeroes.
+     */
+    bool (*bdrv_has_discard_zeroes)(BlockDriverState *bs);
+
+    /*
+     * Returns true if the driver can optimize writing zeroes by discarding
+     * sectors. It is additionally required that the block device is
+     * opened with BDRV_O_UNMAP and the that write zeroes request carries
+     * the BDRV_REQ_MAY_UNMAP flag for this to work.
+     */
+    bool (*bdrv_has_discard_write_zeroes)(BlockDriverState *bs);
+
     QLIST_ENTRY(BlockDriver) list;
 };
 
-- 
1.7.9.5