Re: [PATCH 24/27] block: implement bio helper to add iter kvec pages to bio

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On 12/4/18 7:55 AM, Christoph Hellwig wrote:
> On Fri, Nov 30, 2018 at 07:21:02PM +0000, Al Viro wrote:
>> On Fri, Nov 30, 2018 at 09:56:43AM -0700, Jens Axboe wrote:
>>> For an ITER_KVEC, we can just iterate the iov and add the pages
>>> to the bio directly.
>>
>>> +		page = virt_to_page(kv->iov_base);
>>> +		size = bio_add_page(bio, page, kv->iov_len,
>>> +					offset_in_page(kv->iov_base));
>>
>> Who said that you *can* do virt_to_page() on those?  E.g. vmalloc()'ed
>> addresses are fine for ITER_KVEC, etc.
> 
> In this particular case the caller it seems the callers knows what kind
> of pages we have, but we need to properly document this at the very least.
> 
> Note that in the completely generic case iov_base could also point to
> memory without a struct page at all (e.g. ioremap()ed memory).

That's why I went to ITER_BVEC instead, that's much saner for this
use case.

-- 
Jens Axboe




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