crazyrushstar@xxxxxxxxxxxx wrote: > --- Karen Shaeffer <shaeffer@xxxxxxxxxxxxxxx> 說： >> On Tue, Sep 19, 2006 at 09:48:46PM -0600, Matthew >> Wilcox wrote: >>> Documentation/scsi/scsi_mid_low_api.txt was of >>> immense help to me. This document is indeed essential for low-level driver development. However it doesn't (can't) tell you how to avoid some types of deadlocks. Crazyrushstar, I can't give specific advise about scsi_scan_host() since the code I'm maintaining (sbp2) doesn't use it. However I have some basic suggestions: - Consider your driver a layer between Linux' SCSI core (higher level) and the interconnect software/firmware/hardware, e.g. PCI layer (lower level). Make sure that you first bring up the lower level, then the higher level. Vice versa, bring down the higher level before the lower level on driver shutdown. - AFAIU your driver and everything below it has to be fully able to transfer commands, data and status before it calls scsi_scan_host(). - Also keep the layer paradigm in mind when you design the locking in your driver. Watch out for the host lock which the SCSI core will use on several occasions and which your driver may have to use on some occasions. (The low-level driver I'm maintaining doesn't touch the host lock.) A clearly layered design helps to avoid deadlocks. - Don't use the scsi_block_requests()/ scsi_unblock_requests() API. (The code I'm maintaining is using these, and it is a nightmare because it easily leads into deadlocks. I will rework that driver to not use these calls anymore.) The scsi_block_requests()/ scsi_unblock_requests() API manipulates host state on a low level, subverting the SCSI core's assumptions about host/ target/ LU states. This and similar manipulations of host/ target/ LU state are better _not_ done in a SCSI low-level driver. ... >> I also would purchase the applicable scsi standards. >> >> http://www.t10.org/ The drafts at http://www.t10.org/ftp/t10/drafts/ may suffice too, at least to get started. ... > I have google out a link > "http://www.mjmwired.net/kernel/Documentation/scsi/scsi_mid_low_api.txt"; ... "Documentation/" is a subdirectory of the Linux kernel source distribution. Another essential resource are of course the sources themselves. Good tools to browse the code are Cscope or KScope or LXR: http://free-electrons.com/community/kernel/lxr You certainly already read the sources in include/scsi/. -- Stefan Richter -=====-=-==- =--= =--== http://arcgraph.de/sr/ - 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
