new helper: iov_iter_npages()

counts the pages covered by iov_iter, up to given limit.
do_block_direct_io() and fuse_iter_npages() switched to
it.

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 45204cd5ccd8..0b677f8f9bad 100644
--- a/mm/iov_iter.c
+++ b/mm/iov_iter.c
@@ -262,3 +262,30 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
         return (res == n ? len : res * PAGE_SIZE) - *start;
 }
 EXPORT_SYMBOL(iov_iter_get_pages);
+
+int iov_iter_npages(const struct iov_iter *i, int maxpages)
+{
+        size_t offset = i->iov_offset;
+        size_t size = i->count;
+        const struct iovec *iov = i->iov;
+        int npages = 0;
+        int n;
+
+        for (n = 0; size && n < i->nr_segs; n++, iov++) {
+                unsigned long addr = (unsigned long)iov->iov_base + offset;
+                size_t len = iov->iov_len - offset;
+                offset = 0;
+                if (unlikely(!len))     /* empty segment */
+                        continue;
+                if (len > size)
+                        len = size;
+                npages += (addr + len + PAGE_SIZE - 1) / PAGE_SIZE
+                          - addr / PAGE_SIZE;
+                if (npages >= maxpages) /* don't bother going further */
+                        return maxpages;
+                size -= len;
+                offset = 0;
+        }
+        return min(npages, maxpages);
+}
+EXPORT_SYMBOL(iov_iter_npages);