On Tue, 22 Jul 2003, Adam Migus wrote: > Perhaps I'm not understanding you right but I think Pawel's idea is > cool. It seems to fulfill your requirements (except being network > specific). I suppose if it were network specific we could optimize it > for packet streams and if we made it complicated enough it would require > quite an elaborate sychronization and notification mechanism. Is that > closer to what have in mind?
Well, the case I had particularly in mind was the rapid flow of packets form the kernel to the user process; Pawel's suggestion handles the flow of new data from the user process to the kernel well, and has substantial similarity to some of the IO Lite mechanisms I pointed at (and hopefully with many of the same performance benefits). In the kernel-to-userspace case, we want to avoid the copy of what is originally kernel-owned memory (from the mbuf allocator) to the user process memory. If you didn't care about stuff like confidentiality of kernel memory, etc, the simplest approach would be to actually map the mbuf memory (and possibly cluster) into userspace, and then notify the user process in some form of the new mapping. However, because mbufs and their meta-data aren't page aligned (etc, etc, etc), you really don't want to do it explicitly that way, I suspect. By synchronization, I had in mind a mechanism by which the process and kernel would communicate about memory ownership in the shared memory space: "I'm done with this packet", "I'm done with these packets", "I want to continue delivery of that packet", "I modified this packet", "I'm inserting a new packet here", "I'm dropping this packet", all without extensive memory copying, and with a moderate amount of asynchrony (and possibly parallelism). In terms of functionality, it might be similar to some of the current services that forward between IPDIVERT "in" and "out" (such as natd), or between BPF pseudo-devices. This sounds like something that likely exists in a few commercial products already, so my question to Terry was to whether he knew of any in the literature. IOLite is the closest I know of, as it supports the zero-copy page and memory ownership bits, although I don't know if they allowed it to handle packets, perhaps just datagrams and streams. Robert N M Watson FreeBSD Core Team, TrustedBSD Projects [EMAIL PROTECTED] Network Associates Laboratories _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
