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authorKent Overstreet <kent.overstreet@gmail.com>2016-10-31 11:59:24 -0600
committerJens Axboe <axboe@fb.com>2016-11-02 10:50:18 -0600
commit2cefe4dbaadf83b236caab46705b4b5a4958e3b6 (patch)
treebee7e525f1145ad55b6abd02f97d10222ae90cc9 /block/bio.c
parent13edd5e7315a26b448c5f7f33fc7721b1e0c17ef (diff)
block: add bio_iov_iter_get_pages()
This is a helper that pins down a range from an iov_iter and adds it to a bio without requiring a separate memory allocation for the page array. It will be used for upcoming direct I/O implementations for block devices and iomap based file systems. Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> [hch: ported to the iov_iter interface, renamed and added comments. All blame should be directed to me and all fame should go to Kent after this!] Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/bio.c')
-rw-r--r--block/bio.c49
1 files changed, 49 insertions, 0 deletions
diff --git a/block/bio.c b/block/bio.c
index db85c5753a76..2cf6ebabc68c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -847,6 +847,55 @@ done:
}
EXPORT_SYMBOL(bio_add_page);
+/**
+ * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
+ * @bio: bio to add pages to
+ * @iter: iov iterator describing the region to be mapped
+ *
+ * Pins as many pages from *iter and appends them to @bio's bvec array. The
+ * pages will have to be released using put_page() when done.
+ */
+int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
+{
+ unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
+ struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
+ struct page **pages = (struct page **)bv;
+ size_t offset, diff;
+ ssize_t size;
+
+ size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
+ if (unlikely(size <= 0))
+ return size ? size : -EFAULT;
+ nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
+
+ /*
+ * Deep magic below: We need to walk the pinned pages backwards
+ * because we are abusing the space allocated for the bio_vecs
+ * for the page array. Because the bio_vecs are larger than the
+ * page pointers by definition this will always work. But it also
+ * means we can't use bio_add_page, so any changes to it's semantics
+ * need to be reflected here as well.
+ */
+ bio->bi_iter.bi_size += size;
+ bio->bi_vcnt += nr_pages;
+
+ diff = (nr_pages * PAGE_SIZE - offset) - size;
+ while (nr_pages--) {
+ bv[nr_pages].bv_page = pages[nr_pages];
+ bv[nr_pages].bv_len = PAGE_SIZE;
+ bv[nr_pages].bv_offset = 0;
+ }
+
+ bv[0].bv_offset += offset;
+ bv[0].bv_len -= offset;
+ if (diff)
+ bv[bio->bi_vcnt - 1].bv_len -= diff;
+
+ iov_iter_advance(iter, size);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
+
struct submit_bio_ret {
struct completion event;
int error;