On Fri, May 1, 2015 at 11:42 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > On Fri, 2015-05-01 at 13:43 -0400, Eric B Munson wrote: >> In order to enable policy decisions in userspace, the data contained in >> the SYN packet would be useful for tracking or identifying connections. >> Only parts of this data are available to userspace after the hand shake >> is completed. This patch exposes a new setsockopt() option that will, >> when used with a listening socket, ask the kernel to cache the skb >> holding the SYN packet for retrieval later. The SYN skbs will not be >> saved while the kernel is in syn cookie mode. >> >> The same option will ask the kernel for the packet headers when used >> with getsockopt() with the socket returned from accept(). The cached >> packet will only be available for the first getsockopt() call, the skb >> is consumed after the requested data is copied to userspace. Subsequent >> calls will return -ENOENT. Because of this behavior, getsockopt() will >> return -E2BIG if the caller supplied a buffer that is too small to hold >> the skb header. >> >> Signed-off-by: Eric B Munson <emunson@xxxxxxxxxx> >> Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx> >> Cc: James Morris <jmorris@xxxxxxxxx> >> Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx> >> Cc: Patrick McHardy <kaber@xxxxxxxxx> >> Cc: netdev@xxxxxxxxxxxxxxx >> Cc: linux-api@xxxxxxxxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx >> --- > > We have a similar patch here at Google, but we do not hold one skb and > dst per saved syn. That can be ~4KB for some drivers. > > Only a kmalloc() with the needed part (headers), usually less than 128 > bytes. We store the length in first byte of this allocation. > > This has a huge difference if you want to have ~4 million request socks. > +1 on kmalloc solution. I posted a similar patch a couple of years ago https://patchwork.ozlabs.org/patch/146034/. There was pushback on memory usage and this having to narrow of a use case. Tom > > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
