Messages in this thread | | | Date | Fri, 27 Jan 2023 00:44:08 +0100 | Subject | Re: [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator | From | David Hildenbrand <> |
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On 26.01.23 23:36, Al Viro wrote: > On Thu, Jan 26, 2023 at 09:59:36PM +0000, Al Viro wrote: >> On Thu, Jan 26, 2023 at 02:16:20PM +0000, David Howells wrote: >> >>> +/** >>> + * iov_iter_extract_will_pin - Indicate how pages from the iterator will be retained >>> + * @iter: The iterator >>> + * >>> + * Examine the iterator and indicate by returning true or false as to how, if >>> + * at all, pages extracted from the iterator will be retained by the extraction >>> + * function. >>> + * >>> + * %true indicates that the pages will have a pin placed in them that the >>> + * caller must unpin. This is must be done for DMA/async DIO to force fork() >>> + * to forcibly copy a page for the child (the parent must retain the original >>> + * page). >>> + * >>> + * %false indicates that no measures are taken and that it's up to the caller >>> + * to retain the pages. >>> + */ >>> +static inline bool iov_iter_extract_will_pin(const struct iov_iter *iter) >>> +{ >>> + return user_backed_iter(iter); >>> +} >>> + >> >> Wait a sec; why would we want a pin for pages we won't be modifying? >> A reference - sure, but... > > After having looked through the earlier iterations of the patchset - > sorry, but that won't fly for (at least) vmsplice(). There we can't > pin those suckers;
We'll need a way to pass FOLL_LONGTERM to pin_user_pages_fast() to handle such long-term pinning as vmsplice() needs. But the release path (unpin) will be the same.
-- Thanks,
David / dhildenb
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