[Lustre-devel] Query to understand the Lustre request/reply message

[Andreas Dilger]

On 2010-10-13, at 23:18, Nicolas Williams wrote:
> On Thu, Oct 14, 2010 at 06:38:16AM +0300, Alexey Lyashkov wrote:
>> On Oct 14, 2010, at 03:28, Nicolas Williams wrote:
>>> Yes, it's possible to add buffers to requests.  It's not possible to add
>>> buffers to _replies_ to existing RPCs unless you know the client expects
>>> those additional buffers -- existing clients expect a given maxsize for
>>> each reply, and if your reply is bigger then it will get dropped.
>> It is wrong for last ~1year.
>> ~1year ago i add code to ptlrpc layer which a adjust buffer for reply, and resend a request.
> 
> Ah, I didn't know that was in 1.8.  Are there interop issues (with older
> clients) though with sending larger replies than expected?

Nico, it has always been possible in the past to increase the size of any buffer in a request, or in a reply (if the total reply size will fit into the pre-allocated reply buffer).  An older peer would just ignore the bytes beyond the known part of the buffer.

Is that not true with the 2.x RPC handling?


Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.