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. -- 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
