Subject: Re: zbufs for NetBSD
To: None <>
From: David Laight <>
List: tech-kern
Date: 09/06/2002 18:14:46
> The only thing that is missing is a callback to userspace when the NIC
> is finished with the buffer.  This could be achieved with a normal POSIX
> Async I/O implementation.

The 'feature' of certain widnose network interfaces causes serious
grief.  The data buffer acnnot be released back to the application
until the data has acknowleged by the remote system.

Variations in the ack strateges and window sizes of different
implementations and protocol stacks can very easily lead to the
application stalling until a timer somewhere expires.

It is certainly valid (but not necessarily by TCP) for the
remote system to respond at the application layer before the
request data has been acked by the transport layer.
Getting support for this right in the application starts
getting too hard.....


David Laight: