[Lustre-devel] client-side reply handling

[Robert Read]

On Dec 3, 2009, at 13:17 , Andreas Dilger wrote:

> On 2009-12-03, at 08:00, Eric Barton wrote:
>> Edited from IRC...
>>> 
>>> <Liang> eeb_: do you mean, we can be 100% sure it's safe to unpack
>>>       in-place only when the buffer is unlinked? so it is better
>>>       to unregister reply buffer before calling into
>>>       after_reply()->unpack_reply()?
>> 
>> Yes, I think so.  While the reply buffer remains attached, it's
>> possible to overwrite it at any time.  This could happen if...
>> 
>> a) The server is buggy or malign
> 
> Let's hope we never have to worry about malicious server nodes...
> 
>> b) The request is re-sent and the same reply matchbits are used,
>>  which is what I think happens currently for non-bulk reqs.
> 
> In theory, the reply to the re-sent request should be identical due
> to reply reconstruction, so it shouldn't matter if it happens to
> overwrite the same buffer.

That's fine as long as the buffer is unlinked from the net before it gets swabbed, but hopefully that's the case already. 

robert