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Added a comment about why trying to make a one-behind cache for

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the route in ip_output() is a bad idea.
This commit is contained in:
Garrett Wollman 1995-12-19 21:24:19 +00:00
parent ce29ab3ac6
commit 994fdef98a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=12934
1 changed files with 18 additions and 1 deletions
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19
sys/netinet/ip_output.c
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@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)ip_output.c 8.3 (Berkeley) 1/21/94
* $Id: ip_output.c,v 1.25 1995/11/14 20:34:19 phk Exp $
* $Id: ip_output.c,v 1.26 1995/12/05 17:46:15 wollman Exp $
*/
#include <sys/param.h>
@ -91,6 +91,23 @@ ip_output(m0, opt, ro, flags, imo)
register struct mbuf *m = m0;
register int hlen = sizeof (struct ip);
int len, off, error = 0;
/*
* It might seem obvious at first glance that one could easily
* make a one-behind cache out of this by simply making `iproute'
* static and eliminating the bzero() below. However, this turns
* out not to work, for two reasons:
*
* 1) This routine needs to be reentrant. It can be called
* recursively from encapsulating network interfaces, and it
* is always called recursively from ip_mforward().
*
* 2) You turn out not to gain much. There is already a one-
* behind cache implemented for the specific case of forwarding,
* and sends on a connected socket will use a route associated
* with the PCB. The only cases left are sends on unconnected
* and raw sockets, and if these cases are really significant,
* something is seriously wrong.
*/
struct route iproute;
struct sockaddr_in *dst;
struct in_ifaddr *ia;