DOS clients slow on Samba 4.1.7+ (bug 10422)

[Dominic Raferd]

Sorry I am not a Samba technical expert, but I believe there is a new 
and quite severe bug for Samba 4.1.7+ introduced by bug fix 10422. 
Although intended to cope with max xmit > 64kb it is having unintended 
negative consequences for legacy client machines using DOS.

This message appears hundreds of thousands of times in logs (even with 
log level 0), and file accesses are slow slow slow:

   reply_read: requested read size (1024) is greater than maximum 
allowed (972/1024). Returning short read of maximum allowed for 
compatibility with Windows 2000.

The problem seems to be that samba has max_send is 972 and the new 
bugfix code therefore blocks a *read* size of 1024. However the 
connections for these clients always worked perfectly before with the 
old test (which was against *max_recv* instead of max_send) (e.g. with 
Samba 4.1.5).

The protocol my DOS clients are using is what Samba calls 'LANMAN2' 
(Microsoft Networking).

I have tried different smb.conf settings (max xmit, socket options 
SO_SNDBUG and SO_RCVBUF) and also varied settings on the DOS clients, 
all to no avail. My conclusion is that Samba 4.1.7+ is broken, or at 
least badly wounded, for these clients.

I would be very grateful if it could be fixed!

Dominic