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

[Jens Axboe]

On 11/30/18 1:15 PM, Jens Axboe wrote:
> On 11/30/18 12:21 PM, 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.
> 
> Then how do you set up a kvec based iter with memory you can safely
> DMA to/from?

Would this make you happy:

if (!is_vmalloc_addr(kv->iov_base))
        page = virt_to_page(kv->iov_base);
else
        page = vmalloc_to_page(kv->iov_base);

-- 
Jens Axboe