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From: Eric Blake <eblake@redhat.com>
To: Peter Krempa <pkrempa@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-block@nongnu.org, mreitz@redhat.com, berto@igalia.com,
	qemu-devel@nongnu.org,
	"stefanha@redhat.com" <stefanha@redhat.com>,
	Markus Armbruster <armbru@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v2 10/10] file-posix: Make auto-read-only dynamic
Date: Mon, 11 Mar 2019 15:10:36 -0500	[thread overview]
Message-ID: <74cc34ed-a60b-75fd-3cf1-122ba485917e@redhat.com> (raw)
In-Reply-To: <20190311195925.GA21327@angien.pipo.sk>

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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

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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  reply	other threads:[~2019-03-11 20:20 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-11 16:50 [Qemu-devel] [PATCH v2 00/10] file-posix: Make auto-read-only dynamic Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 01/10] tests/virtio-blk-test: Disable auto-read-only Kevin Wolf
2019-03-12  2:50   ` Eric Blake
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 02/10] qemu-iotests: commit to backing file with auto-read-only Kevin Wolf
2019-03-12  2:52   ` Eric Blake
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 03/10] block: Avoid useless local_err Kevin Wolf
2019-03-11 17:00   ` Kevin Wolf
2019-03-12  2:53   ` Eric Blake
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 04/10] block: Make permission changes in reopen less wrong Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 05/10] file-posix: Fix bdrv_open_flags() for snapshot=on Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 06/10] file-posix: Factor out raw_reconfigure_getfd() Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 07/10] file-posix: Store BDRVRawState.reopen_state during reopen Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 08/10] file-posix: Lock new fd in raw_reopen_prepare() Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 09/10] file-posix: Prepare permission code for fd switching Kevin Wolf
2019-03-11 16:50 ` [Qemu-devel] [PATCH v2 10/10] file-posix: Make auto-read-only dynamic Kevin Wolf
2019-03-11 17:26   ` Eric Blake
2019-03-11 19:59     ` Peter Krempa
2019-03-11 20:10       ` Eric Blake [this message]
2019-03-11 20:25         ` Peter Krempa
2019-03-11 21:15           ` Markus Armbruster
2019-04-29 20:16   ` [Qemu-devel] [Qemu-block] " Max Reitz
2019-04-30 11:31     ` Kevin Wolf
2019-04-30 11:31       ` Kevin Wolf
2019-03-11 20:38 ` [Qemu-devel] [PATCH v2 00/10] " Peter Krempa

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