[v6] block: Deal with filters

[Qemu-devel] [PATCH v6 23/42] blockdev: Use CAF in external_snapshot_prepare()

Posted by Max Reitz 6 years, 3 months ago

This allows us to differentiate between filters and nodes with COW
backing files: Filters cannot be used as overlays at all (for this
function).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 blockdev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 29c6c6044a..c540802127 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1664,7 +1664,12 @@ static void external_snapshot_prepare(BlkActionState *common,
         goto out;
     }
 
-    if (state->new_bs->backing != NULL) {
+    if (state->new_bs->drv->is_filter) {
+        error_setg(errp, "Filters cannot be used as overlays");
+        goto out;
+    }
+
+    if (bdrv_filtered_cow_child(state->new_bs)) {
         error_setg(errp, "The overlay already has a backing image");
         goto out;
     }
-- 
2.21.0

Re: [Qemu-devel] [PATCH v6 23/42] blockdev: Use CAF in external_snapshot_prepare()

Posted by Kevin Wolf 6 years, 2 months ago

Am 09.08.2019 um 18:13 hat Max Reitz geschrieben:
> This allows us to differentiate between filters and nodes with COW
> backing files: Filters cannot be used as overlays at all (for this
> function).
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Didn't we occasionally advertise blockdev-snapshot as the way to insert
filters on top at runtime? Though it seems it has always only worked for
filters that use bs->backing, among which I think there aren't any
user-creatable ones. So we're probably good.

Kevin

>  blockdev.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 29c6c6044a..c540802127 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1664,7 +1664,12 @@ static void external_snapshot_prepare(BlkActionState *common,
>          goto out;
>      }
>  
> -    if (state->new_bs->backing != NULL) {
> +    if (state->new_bs->drv->is_filter) {
> +        error_setg(errp, "Filters cannot be used as overlays");
> +        goto out;
> +    }
> +
> +    if (bdrv_filtered_cow_child(state->new_bs)) {
>          error_setg(errp, "The overlay already has a backing image");
>          goto out;
>      }
> -- 
> 2.21.0
>

Re: [Qemu-devel] [PATCH v6 23/42] blockdev: Use CAF in external_snapshot_prepare()

Posted by Max Reitz 6 years, 2 months ago

On 10.09.19 17:02, Kevin Wolf wrote:
> Am 09.08.2019 um 18:13 hat Max Reitz geschrieben:
>> This allows us to differentiate between filters and nodes with COW
>> backing files: Filters cannot be used as overlays at all (for this
>> function).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> 
> Didn't we occasionally advertise blockdev-snapshot as the way to insert
> filters on top at runtime?

I can only remember advertising for it as the only graph manipulation
tool we had, and maybe saying “We’d want something like
blockdev-snapshot for filters, too”.

Max

> Though it seems it has always only worked for
> filters that use bs->backing, among which I think there aren't any
> user-creatable ones. So we're probably good.
> 
> Kevin
> 
>>  blockdev.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 29c6c6044a..c540802127 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -1664,7 +1664,12 @@ static void external_snapshot_prepare(BlkActionState *common,
>>          goto out;
>>      }
>>  
>> -    if (state->new_bs->backing != NULL) {
>> +    if (state->new_bs->drv->is_filter) {
>> +        error_setg(errp, "Filters cannot be used as overlays");
>> +        goto out;
>> +    }
>> +
>> +    if (bdrv_filtered_cow_child(state->new_bs)) {
>>          error_setg(errp, "The overlay already has a backing image");
>>          goto out;
>>      }
>> -- 
>> 2.21.0
>>