In the common case, qcow2_co_pwrite_zeroes() already only modifies
metadata case, so we're fine with or without BDRV_REQ_NO_FALLBACK set.

The only exception is when using an external data file, where the
request is passed down to the block driver of the external data file. We
are forwarding the BDRV_REQ_NO_FALLBACK flag there, though, so this is
fine, too.

Declare the flag supported therefore.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index b201383c3d..3fa10bf807 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1722,7 +1722,8 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
         }
     }
 
-    bs->supported_zero_flags = header.version >= 3 ? BDRV_REQ_MAY_UNMAP : 0;
+    bs->supported_zero_flags = header.version >= 3 ?
+                               BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK : 0;
 
     /* Repair image if dirty */
     if (!(flags & (BDRV_O_CHECK | BDRV_O_INACTIVE)) && !bs->read_only &&
-- 
2.20.1

On 11/22/19 10:05 AM, Kevin Wolf wrote:
> In the common case, qcow2_co_pwrite_zeroes() already only modifies
> metadata case, so we're fine with or without BDRV_REQ_NO_FALLBACK set.
> 
> The only exception is when using an external data file, where the
> request is passed down to the block driver of the external data file. We
> are forwarding the BDRV_REQ_NO_FALLBACK flag there, though, so this is
> fine, too.
> 
> Declare the flag supported therefore.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   block/qcow2.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index b201383c3d..3fa10bf807 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1722,7 +1722,8 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
>           }
>       }
>   
> -    bs->supported_zero_flags = header.version >= 3 ? BDRV_REQ_MAY_UNMAP : 0;
> +    bs->supported_zero_flags = header.version >= 3 ?
> +                               BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK : 0;
>   
>       /* Repair image if dirty */
>       if (!(flags & (BDRV_O_CHECK | BDRV_O_INACTIVE)) && !bs->read_only &&
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

On Fri 22 Nov 2019 05:05:06 PM CET, Kevin Wolf wrote:
> In the common case, qcow2_co_pwrite_zeroes() already only modifies
> metadata case, so we're fine with or without BDRV_REQ_NO_FALLBACK set.
>
> The only exception is when using an external data file, where the
> request is passed down to the block driver of the external data file. We
> are forwarding the BDRV_REQ_NO_FALLBACK flag there, though, so this is
> fine, too.
>
> Declare the flag supported therefore.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

On 22.11.19 17:05, Kevin Wolf wrote:
> In the common case, qcow2_co_pwrite_zeroes() already only modifies
> metadata case, so we're fine with or without BDRV_REQ_NO_FALLBACK set.
> 
> The only exception is when using an external data file, where the
> request is passed down to the block driver of the external data file. We
> are forwarding the BDRV_REQ_NO_FALLBACK flag there, though, so this is
> fine, too.
> 
> Declare the flag supported therefore.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>