new helper: iov_iter_get_pages()

iov_iter_get_pages(iter, pages, maxsize, &start) grabs references pinning
the pages of up to maxsize of (contiguous) data from iter.  Returns the
amount of memory grabbed or -error.  In case of success, the requested
area begins at offset start in pages[0] and runs through pages[1], etc.
Less than requested amount might be returned - either because the contiguous
area in the beginning of iterator is smaller than requested, or because
the kernel failed to pin that many pages.

direct-io.c switched to using iov_iter_get_pages()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 27 insertions, 0 deletions

diff --git a/mm/iov_iter.c b/mm/iov_iter.c
index e2c9a2db4350..45204cd5ccd8 100644
--- a/mm/iov_iter.c
+++ b/mm/iov_iter.c
@@ -235,3 +235,30 @@ void iov_iter_init(struct iov_iter *i, int direction,
         i->count = count;
 }
 EXPORT_SYMBOL(iov_iter_init);
+
+ssize_t iov_iter_get_pages(struct iov_iter *i,
+                   struct page **pages, size_t maxsize,
+                   size_t *start)
+{
+        size_t offset = i->iov_offset;
+        const struct iovec *iov = i->iov;
+        size_t len;
+        unsigned long addr;
+        int n;
+        int res;
+
+        len = iov->iov_len - offset;
+        if (len > i->count)
+                len = i->count;
+        if (len > maxsize)
+                len = maxsize;
+        addr = (unsigned long)iov->iov_base + offset;
+        len += *start = addr & (PAGE_SIZE - 1);
+        addr &= ~(PAGE_SIZE - 1);
+        n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
+        res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, pages);
+        if (unlikely(res < 0))
+                return res;
+        return (res == n ? len : res * PAGE_SIZE) - *start;
+}
+EXPORT_SYMBOL(iov_iter_get_pages);