Hi all, I'm working on one implementation of FIP for FCoE. FIP is the FCoE initialization protocol, which is used to discover which MAC address to use to get to a Fibre-Channel fabric. In this way it is somewhat like IPv6 neighbor discovery. It also performs keep-alives to detect when connectivity is lost. There has been some mention that this should be done in user space because the iSCSI equivalent was done that way. I'd like to know your opinions on whether I should go forward with an in-kernel module implementation or if that is unlikely to be accepted. The protocol is fairly simple, the resulting code adds only 8K bytes of text to the FCoE module, and none to the base kernel. Here are some rationales for putting this in the FCoE module: 1. It's simpler. A user-based implementation would have to have communication code to talk to the kernel FCoE, to send it the parameters learned by discovery. 2. It uses less memory. It is required for FCoE and since it would be part of the fcoe module it would not take kernel memory unless fcoe is in use. It wouldn't need as much code space (see 1) or the overhead of a process. A kernel implementation should be about 1200 lines or 8K bytes. 3. It is easier to distribute. In the kernel, it's always in sync with the module. There are no interoperability issues as there would be between a user-level implementation and the fcoe driver. Distros would have to take care of more startup issues if there were a user-level daemon. 4. It is better for FCoE "HBA"s. Some FCoE device drivers won't have a netdev interface, so if FIP is user-level, they would have to add something to allow them to send and receive FIP frames, or add a netlink interface (see point 1). 5. It's easier to keep common between LLDs. A user-level implementation may need to be aware of the quirks of the various hardware implementations. The other HBAs coming may be forced to do their own implementations in the kernel anyway. or add patches to the user-mode implementation, see (3). 5. It simplifies correctness issues. In the kernel we can hold locks so that the state changes decided by FIP and by the upper layers can be acted on atomicly. 6. Fewer soft "real-time" issues. FIP involves keep-alives and link-resets, which may be critical to system operation. A user-level process would have to address these needs. The timing isn't too constraining, but the process shouldn't be delayed by very much or storage connectivity could be lost. The daemon shouldn't be swapped out, especially not to an FCoE drive! 7. The booting story is simpler. Booting over FCoE would require the user-level discovery to be part of initrd, not too hard, but something to think about. What are the advantages to doing FIP user level? Simpler development? Killable/restartable? Smaller code size in kernel git trees? One point on the user-level side is that if the implementation becomes more complex, it simplifies maintenance. Here are some references for those who might like to dig into this further: FIP patch series (now out of date and missing a few bug fixes): http://www.open-fcoe.org/pipermail/devel/2008-October/001130.html http://www.open-fcoe.org/pipermail/devel/2008-October/001131.html http://www.open-fcoe.org/pipermail/devel/2008-October/001132.html FCoE doc describing FIP: http://www.t11.org/ftp/t11/pub/fc/bb-5/08-569v1.pdf Thanks for your consideration, Joe Eykholt -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
