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Re: [Qemu-devel] [PATCH 1/2] qemu-img: make sure contain the consecutive

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH 1/2] qemu-img: make sure contain the consecutive number of zero bytes
Date: Tue, 25 Apr 2017 14:20:08 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.0

On 04/24/2017 08:50 PM, 858585 jemmy wrote:
> On Mon, Apr 24, 2017 at 10:43 PM, Eric Blake <address@hidden> wrote:
>> On 04/23/2017 09:33 AM, address@hidden wrote:
>>> From: Lidong Chen <address@hidden>
>>> is_allocated_sectors_min don't guarantee to contain the
>>> consecutive number of zero bytes. this patch fixes this bug.
>> This message was sent without an 'In-Reply-To' header pointing to a 0/2
>> cover letter.  When sending a series, please always thread things to a
>> cover letter; you may find 'git config format.coverletter auto' to be
>> helpful.
> Thanks for your kind advises.

>> I seem to recall past attempts to try and patch this function, which
>> were then turned down, although I haven't scrubbed the archives for a
>> quick URL to point to. I'm worried that there are more subtleties here
>> than what you realize.
> Hi Eric:
> Do you mean this URL?
> https://lists.gnu.org/archive/html/qemu-block/2017-01/msg00306.html

Yes, that's probably the one.

> But I think the code is not consistent with qemu-img --help.
> qemu-img --help
>   '-S' indicates the consecutive number of bytes (defaults to 4k) that must
>        contain only zeros for qemu-img to create a sparse image during
>        conversion. If the number of bytes is 0, the source will not be
> scanned for
>        unallocated or zero sectors, and the destination image will always be
>        fully allocated.

If you still think this patch is needed, the best way to convince me of
it is accompany your patch by a qemu-iotests enhancement that covers the
change in behavior (running the test pre-patch would show that we are
broken without the patch, and having the test ensures we can't later
regress).  That's a lot more work than the vague two lines of the commit
message body.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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