protocol validity checks [LWN.net]

protocol validity checks

Posted Feb 1, 2006 3:57 UTC (Wed) by xoddam (subscriber, #2322)
In reply to: That's not the only meaning of that statement by Ross
Parent article: Van Jacobson's network channels

can imagine an internal 'firewall' inspecting the header of each packet traversing a channel from userspace to ensure the app has sufficient privilege to send it. A pipeline stage with negligible performance impact -- it wouldn't thrash the cache, and if it's in the kernel it would involve no extra context switches.

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protocol validity checks

Posted Feb 1, 2006 6:38 UTC (Wed) by cventers (subscriber, #31465) [Link]

Yeah, since you're writing into mapped memory, the kernel can check it
out in place. And since there's no copy, it's going to be hanging out in
the cache when the check has to take place.

protocol validity checks

Posted Feb 3, 2006 4:15 UTC (Fri) by zblaxell (subscriber, #26385) [Link]

kernel can check it out in place...while the user, maybe on another CPU, switches a few bits just after the kernel check but before the network card picks up the data.

Sneaky indeed!

Posted Feb 3, 2006 5:48 UTC (Fri) by xoddam (subscriber, #2322) [Link]

Ok, freely mapped memory doesn't cut it then. I wonder what the
performance impact of changing packet buffers' page permissions would be,
relative to copying (and relative to keeping the TCP implementation in
kernel space)?