[et-mgmt-tools] [patch] virt-convert add disk signature into virt-image format export

[Joey Boggs]

Here's a sample that works, just want to verify it's alright. Is 64MB 
too much/too little to read at one time?


f = open("test.raw","r")
m = sha.new()
while 1:
    chunk = f.read(65536)
    if not chunk:
        break
    m.update(chunk)
print m.hexdigest()



Cole Robinson wrote:
> Joey Boggs wrote:
>   
>>>> It helps code readability if spacing is reasonably
>>>> consistent throughout.
>>>>
>>>> Hmm, so I just tried the above. What that is essentially
>>>> trying to do is read the entire disk into memory, then
>>>> pass it off as a giant string to the sha function. Clearly
>>>> this is not a workable solution. This also applies to
>>>> the virt-image hash changes as well. Haven't looked into
>>>> the correct way to do it though.
>>>>
>>>> This is also a rather large performance drain. So at the
>>>> very least it should not be the default. That said, I
>>>> don't know the optimal way to expose this option, or
>>>> even if we should.
>>>>         
>>> I think this will become important as we look to distribute the 
>>> appliances either via RHN or on public sites. Also.. this makes us a 
>>> bit more consistent with OVF.
>>>
>>> I am fine with making it off by default, and then causing the command 
>>> line to turn it on.
>>>
>>> -- bk
>>>       
>> I'd rather it be right than kill performance and make it unusable at 
>> best, should the imagefile be bigger than the machines memory.  If we 
>> outsource it to run a system command is that feasible, since we're 
>> dealing with big files? I know Cole was against that originally. I'll 
>> keep looking for a better way and cleanup the variables as well. Making 
>> it off by default is probably best too.
>>
>>     
>
> When I was talking about performance, I was addressing the
> 'correct' way to do, when the 'read into memory' piece is
> fixed. Even then, generating a checksum is a very slow
> process if you are using a large disk (I used sha1sum on
> a DVD iso and it took about 3-4 minutes).
>
> So in this case, turning it off by default is the thing to
> do, we can figure out a cli switch to enable it, but this
> is all dependent on determining the correct way to use the
> libraries. You'll just have to use a loop and read in blocks
> of data at a time, and keep passing it to the library to 
> update the hash.
>
> - Cole
>
>