Messages in this thread | | | Date | Fri, 25 Oct 2002 22:24:00 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] 2.5.44-ac3, cciss, more scatter gather elements |
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On Fri, Oct 25 2002, Stephen Cameron wrote: > > Add blk_rq_map_sg_one_by_one function to ll_rw_blk.c in order to allow a low > level driver to map scatter gather elements from the block subsystem one > at a time into device specific data structures instead of having to take > a copy of all of them all at once and then afterwards copy them into a device > specific format. > > To follow, a patch to the cciss driver using this interface which > allows up to 256 scatter gather elements (current limit is 31).
I have to say that I think this patch is ugly, and a complete duplicate of existing code. This is always bad, especially in the case of something not really straight forward (like blk_rq_map_sg()). A hack.
I can understand the need for something like this, for drivers that can't use a struct scatterlist directly. I'd rather do this in a different way, though.
__blk_rq_map(q, rq, sglist, callback) { ... /* do the mapping *. if (sglist) { sglist[nsegs].page = bvec->bv_page; ... } else callback(q, bvec, nsegs); }
blk_rq_map_rq(q, rq, sglist) { return __blk_rq_map(q, rq, sglist, NULL); }
blk_rq_map_callback(q, rq, callback) { return __blk_rq_map(q, rq, NULL, callback); }
Or use a cookie like you currently do.
Oh, and do try to follow the style. It's
if (cond) foo();
not
if (fond) foo();
-- Jens Axboe
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