Russell King wrote:
> On Fri, Jan 27, 2006 at 09:04:33PM +0100, Pierre Ossman wrote:
>
>> Russell King wrote:
>>
>>> I don't see what the problem is. A sg entry is a list of struct page
>>> pointers, an offset, and a size. As such, it can't describe a transfer
>>> which crosses a page because such a structure does not imply that one
>>> struct page follows another struct page.
>>>
>> If the pages do not strictly follow each other then there is a lot of
>> broken code in the kernel. drivers/mmc/mmci.c and drivers/block/ub.c
>> being two occurences since both assume they can access the entire entry
>> through a single mapping.
>>
>
> We don't make that assumption. What we do is:
>
> - map the current sg using kmap_atomic()
> - copy up to sg->length into or out of that mapping
> - unmap current sg
> - if we have reached the end of this sg, move on to the next
>
This it the algorithm I've been following, but...
> What this means is that we assume sg->offset + sg->length <= PAGE_SIZE
>
This doesn't seem to be true. Since when tracking this problem I added
the following:
BUG_ON((host->cur_sg->length + host->cur_sg->offset) > PAGE_SIZE);
which subsequently triggered. That was the start of my quest for how to
do highmem properly.
Rgds
Pierre
-
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]
