[lwip-devel] [bug #42737] TCP_SND_QUEUELEN check in init.c (and comment in opt.h) are slighlty wrong

[Valery Ushakov]

URL:
  <http://savannah.nongnu.org/bugs/?42737>

                 Summary: TCP_SND_QUEUELEN check in init.c (and comment in
opt.h) are slighlty wrong
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: uwe
            Submitted on: Sat 12 Jul 2014 01:04:44 AM GMT
                Category: TCP
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: git head

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Details:

init.c checks that

#if TCP_SND_QUEUELEN < (2 * (TCP_SND_BUF / TCP_MSS))

since for each mss-sized pbuf with data there's another pbuf with header,
hence the factor of two.

The problem is that TCP_MSS is static maximum and actual mss may be smaller -
e.g. IPv6 header is larger than IPv4, so IPv6 mss is smaller.  This leads to a
situation where a write of full TCP_SND_BUF bytes does not fit into
TCP_SND_QUEUELEN limit




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