new helper: dup_iter()

Copy iter and kmemdup the underlying array for the copy.  Returns
a pointer to result of kmemdup() to be kfree()'d later.

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

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 07a022641996f0ccf74cd872ccd9e4bc8aa5f538..71880299ed487b68dc7b278248a4fb29ddb6b6ec 100644 (file)
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -98,6 +98,8 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages,
                        size_t maxsize, size_t *start);
 int iov_iter_npages(const struct iov_iter *i, int maxpages);
 
+const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags);
+
 static inline size_t iov_iter_count(struct iov_iter *i)
 {
        return i->count;

diff --git a/mm/iov_iter.c b/mm/iov_iter.c
index 827732047da1edc78a323c111e162547286fe638..9d96e283520cc7f3ec27714dfa4abfcb3800e319 100644 (file)
--- a/mm/iov_iter.c
+++ b/mm/iov_iter.c
@@ -751,3 +751,18 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages)
        return npages;
 }
 EXPORT_SYMBOL(iov_iter_npages);
+
+const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
+{
+       *new = *old;
+       if (new->type & ITER_BVEC)
+               return new->bvec = kmemdup(new->bvec,
+                                   new->nr_segs * sizeof(struct bio_vec),
+                                   flags);
+       else
+               /* iovec and kvec have identical layout */
+               return new->iov = kmemdup(new->iov,
+                                  new->nr_segs * sizeof(struct iovec),
+                                  flags);
+}
+EXPORT_SYMBOL(dup_iter);