On Tue, Nov 19, 2019 at 1:11 PM Dongsheng Yang
<dongsheng.yang@xxxxxxxxxxxx> wrote:
>
>
>
> On 11/19/2019 07:59 PM, Ilya Dryomov wrote:
> > 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
>
>
> Right, it's not that easy. Maybe we need another series patches to
> improve it.
Yeah, just watching a header as it is is not going to do it.
Thanks for the review!
Ilya
