Messages in this thread | | | Date | Tue, 17 Jan 2023 09:07:48 +0100 | From | David Hildenbrand <> | Subject | Re: [PATCH v6 03/34] iov_iter: Pass I/O direction into iov_iter_get_pages*() |
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On 17.01.23 08:57, Christoph Hellwig 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?
Agreed. What I understand, David considers that confusing when considering the I/O side of things.
I recall that there is
DMA_BIDIRECTIONAL -> FOLL_WRITE DMA_TO_DEVICE -> !FOLL_WRITE DMA_FROM_DEVICE -> FOLL_WRITE
that used different defines for a different API. Such terminology would be easier to get ... but then, again, not sure if we really need acronyms here.
We're pinning pages and FOLL_WRITE defines how we (pinning the page) are going to access these pages: R/O or R/W. So the read vs. write is never from the POC of the device (DMA read will write to the page).
-- Thanks,
David / dhildenb
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