Re: [Qemu-devel] [PATCH v9 08/10] qcow2: Invoke refcount order amendment function

From: Eric Blake <eblake@redhat.com>
To: Alberto Garcia <berto@igalia.com>, Max Reitz <mreitz@redhat.com>,
	qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v9 08/10] qcow2: Invoke refcount order amendment function
Date: Thu, 6 Aug 2015 21:34:52 -0600	[thread overview]
Message-ID: <55C4275C.50403@redhat.com> (raw)
In-Reply-To: <w518u9obggl.fsf@maestria.local.igalia.com>

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On 08/06/2015 09:10 AM, Alberto Garcia wrote:
> On Mon 27 Jul 2015 05:51:38 PM CEST, Max Reitz wrote:
> 
>> +            if (refcount_bits <= 0 || refcount_bits > 64 ||
>> +                !is_power_of_2(refcount_bits))
>> +            {
>> +                error_report("Refcount width must be a power of two and may "
>> +                             "not exceed 64 bits");
>> +                return -EINVAL;
>> +            }
> 
> I guess there's no lower limit needed for this? Doesn't it break
> anything if refcount_bits == 1?

refcount_bits == 1 works just fine - you have an image that can't take
internal snapshots, and has a maximally dense refblock.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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