From: Nir Soffer <nsoffer@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"open list:Block layer core" <qemu-block@nongnu.org>,
Markus Armbruster <armbru@redhat.com>,
QEMU Developers <qemu-devel@nongnu.org>,
Max Reitz <mreitz@redhat.com>, Eric Blake <eblake@redhat.com>
Subject: Re: [PATCH v2 2/1] qemu-img: Add "backing":true to unallocated map segments
Date: Wed, 23 Jun 2021 19:35:42 +0300 [thread overview]
Message-ID: <CAMRbyyusxxze3=2e0qWvL9KJQ1ViR-zJtP7DtaZ+PwCZyxx2-A@mail.gmail.com> (raw)
In-Reply-To: <YNNbg6jU2dD8VNiU@redhat.com>
On Wed, Jun 23, 2021 at 7:04 PM Kevin Wolf <kwolf@redhat.com> wrote:
>
> Am 23.06.2021 um 15:58 hat Nir Soffer geschrieben:
> > On Wed, Jun 23, 2021 at 11:58 AM Kevin Wolf <kwolf@redhat.com> wrote:
> > >
> > > Am 22.06.2021 um 18:56 hat Nir Soffer geschrieben:
> > > > On Tue, Jun 22, 2021 at 6:38 PM Kevin Wolf <kwolf@redhat.com> wrote:
> > > > >
> > > > > Am 11.06.2021 um 21:03 hat Eric Blake geschrieben:
> > > > > > To save the user from having to check 'qemu-img info --backing-chain'
> > > > > > or other followup command to determine which "depth":n goes beyond the
> > > > > > chain, add a boolean field "backing" that is set only for unallocated
> > > > > > portions of the disk.
> > > > > >
> > > > > > Signed-off-by: Eric Blake <eblake@redhat.com>
> > > > > > ---
> > > > > >
> > > > > > Touches the same iotest output as 1/1. If we decide that switching to
> > > > > > "depth":n+1 is too risky, and that the mere addition of "backing":true
> > > > > > while keeping "depth":n is good enough, then we'd have just one patch,
> > > > > > instead of this double churn. Preferences?
> > > > >
> > > > > I think the additional flag is better because it's guaranteed to be
> > > > > backwards compatible, and because you don't need to know the number of
> > > > > layers to infer whether a cluster was allocated in the whole backing
> > > > > chain. And by exposing ALLOCATED we definitely give access to the whole
> > > > > information that exists in QEMU.
> > > > >
> > > > > However, to continue with the bike shedding: I won't insist on
> > > > > "allocated" even if that is what the flag is called internally and
> > > > > consistency is usually helpful, but "backing" is misleading, too,
> > > > > because intuitively it doesn't cover the top layer or standalone images
> > > > > without a backing file. How about something like "present"?
> > > >
> > > > Looks hard to document:
> > > >
> > > > # @present: if present and false, the range is not allocated within the
> > > > # backing chain (since 6.1)
> > >
> > > I'm not sure why you would document it with a double negative.
> > >
> > > > And is not consistent with "offset". It would work better as:
> > > >
> > > > # @present: if present, the range is allocated within the backing
> > > > # chain (since 6.1)
> > >
> > > Completely ignoring the value? I would have documented it like this, but
> > > with "if true..." instead of "if present...".
> >
> > This is fine, but it means that this flag will present in all ranges,
> > instead of only in unallocated ranges (what this patch is doing).
>
> An argument for always having the flag would be that it's probably
> useful for a tool to know whether a given block is actually absent or
> whether it's just running an old qemu-img.
Good point, this is the best option. The disadvantage is a bigger output but
if you use json you don't care about the size of the output.
> If we didn't care about this, I would still define the actual value, but
> also document a default.
>
> Kevin
>
next prev parent reply other threads:[~2021-06-23 16:36 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-11 14:01 [PATCH v2] qemu-img: Make unallocated part of backing chain obvious in map Eric Blake
2021-06-11 14:35 ` Vladimir Sementsov-Ogievskiy
2021-06-11 14:59 ` Eric Blake
2021-06-11 18:13 ` Nir Soffer
2021-06-11 19:03 ` [PATCH v2 2/1] qemu-img: Add "backing":true to unallocated map segments Eric Blake
2021-06-15 8:54 ` Vladimir Sementsov-Ogievskiy
2021-06-15 13:09 ` Nir Soffer
2021-06-22 15:38 ` Kevin Wolf
2021-06-22 16:56 ` Nir Soffer
2021-06-23 8:57 ` Kevin Wolf
2021-06-23 13:58 ` Nir Soffer
2021-06-23 16:04 ` Kevin Wolf
2021-06-23 16:35 ` Nir Soffer [this message]
2021-06-28 17:42 ` Eric Blake
2021-06-29 7:23 ` Vladimir Sementsov-Ogievskiy
2021-06-29 14:40 ` Kevin Wolf
2021-06-29 15:53 ` Nir Soffer
2021-06-22 17:51 ` Vladimir Sementsov-Ogievskiy
2021-06-22 17:04 ` Nir Soffer
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