On 5/26/19 8:51 AM, Christian Svensson wrote:
I am doing some preliminary scouting of how one could add support for
FICON (FC-SB-3 specifically). I am mostly interested in Linux being
able to act as a FICON target for now.
The TL;DR summary for FICON is that it uses Fibre Channel just like FCP/SCSI
up to but not including the FC-4 (FCP) layer. At that point it uses its own
SBCCS layer.
FICON is used by IBM mainframes to interface peripherals like tape, disk,
printers, card punchers/readers, etc. It is more like a mainframe USB/Firewire
than SCSI in that regard.
I would prefer to implement my peripherals in user-space, I don't see any
convincing case for having e.g. a virtual tape drive running in kernel space.
The I/O heavy disks would probably benefit from being in kernel space, but I am
OK limiting the initial scope.
I am 100% new to the SCSI and Fibre Channel subsystem in Linux, and I
do not even know if the current HBAs support sending frames without FCP
but after scouting the code it does seem that it might work out - FCP
seems decoupled enough.
If you want to learn more the standard document Wireshark has an
implementation of the protocol (packet-fcsb3.c/h). If you want all the details
you will sadly have to pay $60 and buy it from INCITS at
https://webstore.ansi.org/Standards/INCITS/INCITS3742003S2013.
Fwiw, FICON uses FC type 0x1B and 0x1C.
Any thoughts or ideas where you would start? Do you see any future for this
addition to the kernel?
Hi Chris,
I'm not sure what the best approach is for the initiator functionality.
For the target functionality you may want to have a look at tcmu
(Documentation/target/tcmu-design.txt and
drivers/target/target_core_user.c). An existing FC target driver is
available in drivers/scsi/qla2xxx/tcm_qla2xxx.c. A diagram that shows
the different functional blocks in TCM is available at
https://en.wikipedia.org/wiki/LIO_(SCSI_target) (LIO is another name for
TCM).
Bart.
