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authorDavid Howells <dhowells@redhat.com>2022-10-28 23:50:30 +0300
committerSteve French <stfrench@microsoft.com>2023-02-21 02:25:43 +0300
commit7d58fe731028128f3a7e20b9c492be48aae133ee (patch)
tree7c5e39d8e329ad2e87114d83e499cd91de5c8f20 /include/linux/uio.h
parentf62e52d1276b6cd329fe72d36bdf912b2ce4caaf (diff)
downloadlinux-7d58fe731028128f3a7e20b9c492be48aae133ee.tar.xz
iov_iter: Add a function to extract a page list from an iterator
Add a function, iov_iter_extract_pages(), to extract a list of pages from an iterator. The pages may be returned with a pin added or nothing, depending on the type of iterator. Add a second function, iov_iter_extract_will_pin(), to determine how the cleanup should be done. There are two cases: (1) ITER_IOVEC or ITER_UBUF iterator. Extracted pages will have pins (FOLL_PIN) obtained on them so that a concurrent fork() will forcibly copy the page so that DMA is done to/from the parent's buffer and is unavailable to/unaffected by the child process. iov_iter_extract_will_pin() will return true for this case. The caller should use something like unpin_user_page() to dispose of the page. (2) Any other sort of iterator. No refs or pins are obtained on the page, the assumption is made that the caller will manage page retention. iov_iter_extract_will_pin() will return false. The pages don't need additional disposal. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jens Axboe <axboe@kernel.dk> cc: Al Viro <viro@zeniv.linux.org.uk> cc: John Hubbard <jhubbard@nvidia.com> cc: David Hildenbrand <david@redhat.com> cc: Matthew Wilcox <willy@infradead.org> cc: linux-fsdevel@vger.kernel.org cc: linux-mm@kvack.org Signed-off-by: Steve French <stfrench@microsoft.com>
Diffstat (limited to 'include/linux/uio.h')
-rw-r--r--include/linux/uio.h27
1 files changed, 26 insertions, 1 deletions
diff --git a/include/linux/uio.h b/include/linux/uio.h
index eec6ed8a627a..514e3b7b06b8 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -361,9 +361,34 @@ static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction,
.count = count
};
}
-
/* Flags for iov_iter_get/extract_pages*() */
/* Allow P2PDMA on the extracted pages */
#define ITER_ALLOW_P2PDMA ((__force iov_iter_extraction_t)0x01)
+ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages,
+ size_t maxsize, unsigned int maxpages,
+ iov_iter_extraction_t extraction_flags,
+ size_t *offset0);
+
+/**
+ * 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);
+}
+
#endif