SMB2/3 Credits (Multi-Credit) support

Christian Ambach ambi at
Fri Jun 29 06:00:39 MDT 2012

On 06/27/2012 11:11 PM, Jeremy Allison wrote:

 > which is fine, but I need to tell you why that was added.
 > What I observed back when we were advertising smaller credit
 > windows was that Windows clients would request sequence numbers
 > *outside* of the valid credit range.
 > For example, if we have a valid sequence number space of 100-200,
 > then Windows clients would use requests with sequence numbers between
 > 100 - 300. Note that they'd never use more than the 100 outstanding
 > credits they had available, but they'd commonly miss a low
 > sequence number and then use numbers above the valid range,
 > finally filling in the missing low sequence number just before
 > running out of credits.
> So DEFAULT_SMB2_MAX_CREDIT_BITMAP_FACTOR was a heuristic added
> to allow us to cope with that. Christian worked with me on
> this and can probably also remember some details.
My impression was that this problem went away after some fixes were 
added to Samba, e.g. the ones that make sure that we properly grant the 
requested credits for compound requests (65566df) and granting credits 
in async replies (ffbd1ed). There might be more changes that were 
involved, but I do not recall seeing the message id gap again in recent 
smbd logs I looked into.

So it seems to me that adding this doubled ranges was more a papering 
over real issues.

I can re-run the tests that hit the wrong message id messages against 
Metze's patches once I am back in the office in about 10 days.


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