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Using PPPD pty option and script: controlling stdin buffer size?


We have a HW/SW set-up using Linux PPP over slow links, and have recently abandoned a solution with a dedicated kernel module driver for our specific hardware, and are now trying a pure user-mode solution using the pty option in pppd. Most if its performance is quite OK, but we see that we do not have complete control of the buffering along the packet signal path. From the PPPD MAN page it says that pty script starts a pseudo-tty instance, and that our script shall read data from it as it was from stdin using read(0,...). THIS WORKS. HOWEVER, since our link is slow we have implemented flow control, and in periods we do not read from stdio. In that period data builds up in stdio, but we see no sigh of data being dropped in the ppp0 interface queue (which is set to 3 packets as is the default value). 

Question: It seems that the stdin interface has a large buffer, much larger than we appreciate. Is there any way we can configure its size, making it smaller?

Best regards,

Arne Lie
SINTEF ICT, Dept. of Communication Systems
NO-7465 Trondheim, NORWAY
Dir. phone +47 73 59 27 03 - mobile +47 450 20 040
e-mail: arne.lie@xxxxxxxxx 

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