Seokmann Ju wrote: > Hi, > > With starting to implement FC-CT/ELS support on the qla2xxx module, I > would like to get some idea about the bidi-bidirectional. Hi Dear Seokmann Searching for "FC-CT ELS" did not produce any comprehensive results for me. If you could send me exact pointer to the t11 paper I could investigate it deeper. > As I understand that the bidi is packet transporting infra-structure, > I think it could be good candidate for the FC specific FC-CT/ELS > packet delivery in between the application and the individual devices > given topology. > bidi, as in scsi-bidirectional commands, is any scsi command (in any command set) where a single CDB utilizes both an in-buffer and an out-buffer, for sending-while-receiving data to-from a target device. The write-from-host buffers and read-to-host buffers happens concurrently with out predetermined serialization and can in fact happen all at once. So to answer your question: It is a must candidate for bidi, if the t11 standard states that a single CDB specifies both an out-buffer and an in-buffer, to complete the command. An example of a bidi command is the XOR family of commands as defined by SCSI for the block command set. > As I have limited understanding about the bid, here are my questions, > 0. would the bidi be a right choice for the FC-CT/ELS packet delivery? Please point me to the normative documentation so I can check. > 1. where should I get any kind of documents/briefs about the bidi? In code and git I'm afraid. Look in git for the history of both drivers/scsi/libiscsi.c and drivers/scsi/scsi_debug.c and see how they are changed to receive bidirectional commands. And also include/scsi/scsi_cmnd.h and drivers/scsi/scsi_lib.c for these patches that introduce the bidi support, they have some explanations and you can inspect their implementation. > 2. which part of code that I have to walk-through for further > understanding about the bidi mechanism? Best is to look in git for the relevant patches both at scsi-midlevel and iscsi. > 3. with the bidi, what's the application interface should look like? > if you have for example: int xxx_write(const void* out_buff, int len); and int xxx_read(void * in_buff, int_len); then you might have something like int xxx_xor(const void* out_buff, void * in_buff, int len); which is a bidi command that writes and reads results all at once. > I expect to have some changes/additions in the FC transport layer in > regards to the support and in general. > > Any comment/guidance would be greatly helpful. > scsi-bidirectional commands was crafted for scsi command sets that specifically called for both in/out buffers participating in a single command. If the commands in question are like that then this is the right tool to use. > Thank you, > Seokmann > -- When you advance farther I can send you code examples of how an initiator pushes block-requests that carry bidi payload that's the easy part. Getting your driver to support and expect bidi commands is a bit harder. (Just a bit) Feel free to ask any questions you have. Cheers Boaz -- 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
