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Re: [Qemu-devel] [PATCH v2 10/10] file-posix: Make auto-read-only dynami
From: |
Peter Krempa |
Subject: |
Re: [Qemu-devel] [PATCH v2 10/10] file-posix: Make auto-read-only dynamic |
Date: |
Mon, 11 Mar 2019 21:25:34 +0100 |
User-agent: |
Mutt/1.11.3 (2019-02-01) |
On Mon, Mar 11, 2019 at 15:10:36 -0500, Eric Blake wrote:
> On 3/11/19 2:59 PM, Peter Krempa wrote:
>
> >> auto-read-only was introduced in 3.1, at which point we intentionally
> >> had sufficiently loose wording to permit (but not require) dynamic state
> >> checking; so you are not breaking the interface. On the other hand, is
> >> libvirt going to have problems introspecting whether it can use
> >> auto-read-only and get the dynamic behavior it needs? Or is there
> >> enough else in the way of libvirt's switch to -blockdev that it won't
> >> attempt anything that needs auto-read-only without other 4.0 interfaces
> >> anyway, at which point detecting the presence of the field (but not
> >> whether the field has a guarantee of dynamic behavior) on 3.1 doesn't
> >> matter?
> >
> > I think we can use Stefan's capability detection mechanism he introduced
> > for the migration with cache enabled for local files to add a flag for
> > this as well.
>
> Except I thought we decided that the most recent version of his QMP
> changes was now fully-introspectible, thanks to using conditional
> compilation.
>
> https://lists.gnu.org/archive/html/qemu-devel/2019-03/msg02510.html
Oh, bummer, I missed that it was no longer needed. I still think it's
worth adding that for future use once it will be necessary to detect
that certain things were patched and require libvirt to change behaviour
if that's the case.
> Well, that may prove to be a short-lived hiatus, if libvirt would
> happily attempt to use qemu 3.1 and fail without some other
> introspectible hook to know whether auto-read-only has required semantics.
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc. +1-919-301-3226
> Virtualization: qemu.org | libvirt.org
>
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[Qemu-devel] [PATCH v2 09/10] file-posix: Prepare permission code for fd switching, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 08/10] file-posix: Lock new fd in raw_reopen_prepare(), Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 07/10] file-posix: Store BDRVRawState.reopen_state during reopen, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 06/10] file-posix: Factor out raw_reconfigure_getfd(), Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 05/10] file-posix: Fix bdrv_open_flags() for snapshot=on, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 04/10] block: Make permission changes in reopen less wrong, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 03/10] block: Avoid useless local_err, Kevin Wolf, 2019/03/11