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/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
