On Fri, Jun 03 2005, Mike Christie wrote: > The following patches should enable the use of scatter lists for all > REQ_BLOCK_PC requests and cleanup some code duplication or dangerous > memory allocations in the dm-multipath hw handlers and > block/scsi_ioctl.c. > > REQ_BLOCK_PC scatter list usage only required converting the old > sg_scsi_ioctl code to do bio backed requests since the current block > layer SG_IO code will always use requests with bios. But while > converting the old ioctl and removing some dangerous (GFP_KERNEL in > failover path) memory allocations from a dm-multipath hw_handler (and > while updating the LSI one) I was able to seperate some common code into > two new functions: blk_rq_map_kern() and bio_map_kern. These functions > are similar to their blk/bio*user cousins where they allocate requests > and bios and setup the data pointers except they work on kernel buffers. Wonderful stuff, much needed for a long time. > The goal is next convert the scsi 'special' requests to use these > functions, so scsi will be able to use block layer functions for scatter > lists setup for all requests. And then hopefully one day we will not > need those stinking "if (sc->use_sg)" paths all over our scsi drivers. I've slowly been doing the same thing in other places in the kernel and this bit has been talked about between James and I for at least a year or two. -- Jens Axboe
