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Re: [PATCH v7 29/47] blockdev: Use CAF in external_snapshot_prepare()
From: |
Max Reitz |
Subject: |
Re: [PATCH v7 29/47] blockdev: Use CAF in external_snapshot_prepare() |
Date: |
Fri, 24 Jul 2020 11:23:48 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
On 20.07.20 18:08, Andrey Shinkevich wrote:
> On 25.06.2020 18:21, Max Reitz wrote:
>> 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>
>> ---
>> blockdev.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 1eb0fcdea2..aabe51036d 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -1549,7 +1549,12 @@ static void
>> external_snapshot_prepare(BlkActionState *common,
>> goto out;
>> }
>> - if (state->new_bs->backing != NULL) {
>> + if (state->new_bs->drv->is_filter) {
>
>
> Is there a chance to get a filter here? If so, is that when a user
> specifies the file name of such a kind “filter[filter-name]:foo.qcow2”
> or somehow else?
It would be with blockdev-snapshot and by specifying a filter for
@overlay. Technically that’s already caught by the check whether the
overlay supports backing images (whether drv->supports_backing is true),
but we might as well give a nicer error message.
Example:
{"execute":"qmp_capabilities"}
{"execute":"blockdev-add","arguments":
{"node-name":"overlay","driver":"copy-on-read",
"file":{"driver":"null-co"}}}
{"execute":"blockdev-add","arguments":
{"node-name":"base","driver":"null-co"}}
{"execute":"blockdev-snapshot","arguments":
{"node":"base","overlay":"overlay"}}
Max
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