new helper: iov_iter_get_pages()

[deliverable/linux.git] / mm / iov_iter.c

diff --git a/mm/iov_iter.c b/mm/iov_iter.c
index e2c9a2db4350a498ab33e1ea38bb4bb9f59ec1ee..45204cd5ccd8a9d5409e337f6a04edc3b722f954 100644 (file)
--- 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);