On Tue, Nov 19, 2019 at 9:50 AM Dongsheng Yang
<dongsheng.yang@xxxxxxxxxxxx> wrote:
>
>
> Hi Ilya,
>
> On 11/18/2019 09:38 PM, Ilya Dryomov wrote:
> > Hello,
> >
> > This series makes read-only mappings compatible with read-only caps:
> > we no longer establish a watch,
>
> Although this is true in userspace librbd, I think that's wired: when
> there is someone is reading this image, it can be removed. And the
> reader will get all zero for later reads.
>
> What about register a watcher but always ack for notifications? Then
> we can prevent removing from image being reading.
We can't register a watch because it is a write operation on the OSD
and we want read-only mappings to be usable with read-only OSD caps:
$ ceph auth add client.ro ... osd 'profile rbd-read-only'
$ sudo rbd map --user ro -o ro ...
Further, while returning zeros if an image or a snapshot is removed is
bad, a watch isn't a good solution. It can be lost, and even when it's
there it's still racy. See the description of patch 7.
Thanks,
Ilya
