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SubjectRe: [PATCH v6 03/34] iov_iter: Pass I/O direction into iov_iter_get_pages*()
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On 17.01.23 09:44, David Howells wrote:
> Christoph Hellwig <hch@infradead.org> wrote:
>
>> On Mon, Jan 16, 2023 at 11:08:24PM +0000, David Howells wrote:
>>> Define FOLL_SOURCE_BUF and FOLL_DEST_BUF to indicate to get_user_pages*()
>>> and iov_iter_get_pages*() how the buffer is intended to be used in an I/O
>>> operation. Don't use READ and WRITE as a read I/O writes to memory and
>>> vice versa - which causes confusion.
>>>
>>> The direction is checked against the iterator's data_source.
>>
>> Why can't we use the existing FOLL_WRITE?
>
> Because FOLL_WRITE doesn't mean the same as WRITE:
>
> (1) It looks like it should really be FOLL_CHECK_PTES_WRITABLE. It's not
> defined as being anything to do with the I/O.

Especially combined with FOLL_FORCE, this is not true.

--
Thanks,

David / dhildenb

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