buglwIP - A Lightweight TCP/IP stack - Bugs: bug #46948, Default TCP_SNDLOWAT invalid when...

 
 

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bug #46948: Default TCP_SNDLOWAT invalid when TCP_SND_BUF > 2*65535

Submitted by:  Joel Cunningham <jcunningham>
Submitted on:  Thu 21 Jan 2016 04:28:01 PM UTC  
 
Category: TCPSeverity: 3 - Normal
Item Group: Faulty BehaviourStatus: Fixed
Privacy: PublicAssigned to: Simon Goldschmidt <goldsimon>
Open/Closed: ClosedPlanned Release: None
lwIP version: git head

Thu 18 Feb 2016 08:37:18 AM UTC, comment #1:

Fixed by checking TCP_SNDLOWAT in init.c.

Simon Goldschmidt <goldsimon>
Project AdministratorIn charge of this item.
Thu 21 Jan 2016 04:28:01 PM UTC, original submission:

The calculation in opt.h for TCP_SNDLOWAT results in a invalid configuration when TCP_SND_BUF is greater than 2*66535.

Due to limitations of tcp_write, tcp_sndbuf() is limited to returning 65535 (even with large send buffers) and when TCP_SNDLOWAT is greater than 65535, we will never pass any checks where tcp_sndbuf() is compared against TCP_SNDLOWAT. This happens once the send buffer is full and then drains, but we never mark the netconn/socket as writable again.

I've changed the value of TCP_SNDLOWAT in my port, but it would be good to update the opt.h calculation to prevent this from happening when TCP_SND_BUF is tuned to be large

Joel Cunningham <jcunningham>
Project Member

 

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  • -unavailable- added by goldsimon (Posted a comment)
  • -unavailable- added by jcunningham (Submitted the item)
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    Follow 3 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Thu 18 Feb 2016 08:37:18 AM UTCgoldsimonStatusNone=>Fixed
      Assigned toNone=>goldsimon
      Open/ClosedOpen=>Closed

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