[Pvfs2-developers] encoding negative responses

[Rob Ross]

Sounds like formalizing this would be a good idea. Is there even one 
counter-example that we can think of or that exists today?

Rob

Pete Wyckoff wrote:
> pcarns at wastedcycles.org wrote on Thu, 19 Oct 2006 16:34 +0200:
>> We've plugged some similar bugs before by just fixing the specific case 
>> (being more careful about cleaning up masks, pointers, sizes, etc. after 
>> an error), and the same could easily be done here.  Should there be a 
>> more general solution, though?
>>
>> What I am wondering is if the response encoder should even bother to 
>> encode the whole message if the status is non-zero.  It seems like if 
>> there is an error code it should just stick to encoding the basic 
>> PVFS_server_resp struct.  The rest of the fields can't really be trusted 
>>  since we hit an error condition.  Likewise on the decode side of things.
>>
>> The lebf_encode_resp() function already sort of catches one case of this:
>>
>>     /* we stand a good chance of segfaulting if we try to encode the 
>> response
>>      * after something bad happened reading data from disk. */
>>     if (resp->status != -PVFS_EIO)
>>     {
>>
>> ... but that only handles one specific error code.
> 
> I'm sort of in agreement with your analysis.  We had a similar issue
> on the decoding side on the client:  an EIO came back from the
> server but the client proceeded to try to decode particular fields.
> 
> http://www.beowulf-underground.org/pipermail/pvfs2-developers/2006-June/002202.html
> 
> Maybe both the lebf_{en,de}code_resp should encode or decode the
> rest of the message if status == 0.  The comparison for EIO alone is
> not sufficient.
> 
> Are there any reasons the client should be looking at more fields
> once it sees a negative status?  Maybe we should just formalize
> this.  And fixup lebf_decode_rel so it only frees things if status
> was zero.
> 
> 		-- Pete
> 
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