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Re: [Qemu-block] [PATCH v3 0/3] qemu-img: Allow rebase with no input bas

From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH v3 0/3] qemu-img: Allow rebase with no input base
Date: Fri, 10 May 2019 11:40:46 +0200
User-agent: Mutt/1.11.3 (2019-02-01)

Am 09.05.2019 um 19:52 hat Max Reitz geschrieben:
> This series allows using qemu-img rebase (without -u) on images that do
> not have a backing file.  Right now, this fails with the rather cryptic
> error message:
> $ qemu-img rebase -b base.qcow2 foo.qcow2
> qemu-img: Could not open old backing file '': The 'file' block driver 
> requires a file name
> Yeah, well, OK.
> With how rebase currently works, this would lead to the overlay being
> filled with zeroes, however.  This is where patch 2 comes in and instead
> makes rebase use blk_pwrite_zeroes() whenever it handles an area past
> the input’s backing file’s EOF.
> (Note that additionally we could try to punch holes in the overlay
> whenever it matches the new backing file, but that’s something I’ll put
> off for later.  (We don’t even have a reliable method for punching holes
> into an overlay yet, although I would like to have such because it could
> make active commit more efficient.))
> And patch 3 adds the usual test.
> v3:
> - Patch 3: Move test to own file so it doesn’t run for qed or qcow2 v2
>   (because it can’t, it requires zero clusters)

Thanks, updated in the block branch.


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