From: Linus Torvalds <[EMAIL PROTECTED]> Date: Wed, 17 Oct 2007 18:07:19 -0700 (PDT)
> sg_next() - as it stands now - never actually looks at the SG that its > argument points to: it explicitly *only* looks at the next one. > > That's the bug. If sg_next() looked at the actual *current* sg entry, we > wouldn't have any issues to begin with, and that's what I'm arguing we > should do in the longer run (where "longer run" is defined as "when Jens > does it asap"). What the thing really wants is some kind of indication of state, without having to bloat up the scatterlist structure. I believe that we have enough of a limited set of accessors to sg->page that we can more aggressively encode things in the lower bits. I'm thinking of encoding the low two bits of sg->page as follows: 1) bits == 0 then the SG list is linear and sg_next() is sg++ 2) bits == 1 the nest SG is an indirect chunk, sg_next() is therefore something like: next = *((struct scatterlist **)(sg + 1)); 3) bits == 2 this is the last entry in the scatterlist, sg_next() is NULL So for the cases of ARCH_HAS_SG_CHAIN not being set (ie. back compatible), we can do no bit encoding in page->flags and just do sg_next() == sg++, as is done now. When doing SG chaining, in each non-linear chunk we have to allocate one more pointer past the end of the scatterlist array (instead of a full extra scatterlist entry for the indirect pointer encode). Next, all sg->page accesses have to be guarded to clear the state bits out first. I don't know, maybe it would work, and would make the loop termination issues easier to handle properly. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/