Re: [Qemu-devel] [PATCH for-4.0 v3 0/6] NBD server alignment improvement

[Eric Blake]

On 3/29/19 3:30 PM, Eric Blake wrote:

>> ... yet the 2^63-512 image can be opened (same as before):
>>
>>   $ ./nbdkit -U - memory size=$((2**63 - 512)) --run 'qemu-img info $nbd'
>>   image: nbd+unix://?socket=/tmp/nbdkitHSAzNz/socket
>>   file format: raw
>>   virtual size: -8388607T (9223372036854775296 bytes)
>>   disk size: unavailable
>>
>> I've just noticed that the virtual size negative (also in upstream
>> qemu).  That looks like a bug too ...
> 
> Yes, it does. I'll see if I can find a quick fix for that formatting
> routine.
> 

qemu-img is calling block/qapi.c:get_human_readable_size(), which stops
at T, and has indeed has some horrible overflow problems, such as:
                         ((size + (base >> 1)) / base),
without regards to whether int64_t size is near maximum before the addition.

Other places in the code base use util/cutils.c:size_to_str(), which
handles all the way up to E, and appears to be a bit saner.

Why we have to separate integer-to-human converters, where one is rather
buggy, is beyond me.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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