On Fri, May 1, 2015 at 1:01 PM, Eric B Munson <emunson@xxxxxxxxxx> wrote: > On Fri, 01 May 2015, Andy Lutomirski wrote: > >> On Fri, May 1, 2015 at 10:43 AM, Eric B Munson <emunson@xxxxxxxxxx> 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. >> >> What's the purpose and what headers are you returning? > > Currently the ethernet, IP, and TCP headers are being returned. The IP > and TCP headers will be used by userspace to make decisions on how to > handle incoming connections. The ethernet headers are being returned > for completeness, I would be fine not including them in what is copied > if that is a concern, however the team requesting this change here > requires the IP and TCP headers. > >> >> There was a bit of a mixup with tx timestamps where the set of headers >> returned was possibly excessive and incompletely thought out the first >> time around. > > With this in mind, we could drop copying the ethernet headers and simply > hold onto the IP and TCP headers. That's probably better. If nothing else, you avoid breaking userspace when you're not using Ethernet. --Andy -- 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
