Re: [Qemu-devel] [RFC] Block device size rounding

[Eric Blake]

On 10/12/2015 09:56 AM, John Snow wrote:

>> What is the correct action here though? If the file is writeable should
>> we just allow the device to extend its size? Is that possible already?
>> Just zero-pad read-only?
>>
> 
> Read-only seems like an easy case of append zeroes.

Yes, allowing read-only with append-zero behavior seems sane.

> 
> Read-write ... well, we can't write-protect just half of a 512k block.

> Probably just forcibly increasing the size on RW or refusing to use the
> file altogether are probably the sane deterministic things we want.

I'd lean towards outright rejection if the file size isn't up to snuff
for use as read-write.  Forcibly increasing the size (done
unconditionally) still feels like magic, and may not be possible if the
size is due to something backed by a block device rather than a file.

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

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