iov_iter: add copy_to_user support

This adds iov_iter wrappers around copy_to_user() to match the existing
wrappers around copy_from_user().

This will be used by the generic file system buffered read path.

Signed-off-by: Zach Brown <zab@zabbo.net>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>

diff --git a/fs/iov-iter.c b/fs/iov-iter.c
index 563a6bab0a810129d3833fc514e05d6169b02c7e..0b2407e9877cbca4a8c8ec723005a8e7295614ac 100644 (file)
--- a/fs/iov-iter.c
+++ b/fs/iov-iter.c
@@ -6,6 +6,86 @@
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
 
+static size_t __iovec_copy_to_user(char *vaddr, const struct iovec *iov,
+                                  size_t base, size_t bytes, int atomic)
+{
+       size_t copied = 0, left = 0;
+
+       while (bytes) {
+               char __user *buf = iov->iov_base + base;
+               int copy = min(bytes, iov->iov_len - base);
+
+               base = 0;
+               if (atomic)
+                       left = __copy_to_user_inatomic(buf, vaddr, copy);
+               else
+                       left = copy_to_user(buf, vaddr, copy);
+               copied += copy;
+               bytes -= copy;
+               vaddr += copy;
+               iov++;
+
+               if (unlikely(left))
+                       break;
+       }
+       return copied - left;
+}
+
+/*
+ * Copy as much as we can into the page and return the number of bytes which
+ * were sucessfully copied.  If a fault is encountered then return the number of
+ * bytes which were copied.
+ */
+size_t iov_iter_copy_to_user_atomic(struct page *page,
+               struct iov_iter *i, unsigned long offset, size_t bytes)
+{
+       char *kaddr;
+       size_t copied;
+
+       BUG_ON(!in_atomic());
+       kaddr = kmap_atomic(page);
+       if (likely(i->nr_segs == 1)) {
+               int left;
+               char __user *buf = i->iov->iov_base + i->iov_offset;
+               left = __copy_to_user_inatomic(buf, kaddr + offset, bytes);
+               copied = bytes - left;
+       } else {
+               copied = __iovec_copy_to_user(kaddr + offset, i->iov,
+                                             i->iov_offset, bytes, 1);
+       }
+       kunmap_atomic(kaddr);
+
+       return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_to_user_atomic);
+
+/*
+ * This has the same sideeffects and return value as
+ * iov_iter_copy_to_user_atomic().
+ * The difference is that it attempts to resolve faults.
+ * Page must not be locked.
+ */
+size_t iov_iter_copy_to_user(struct page *page,
+               struct iov_iter *i, unsigned long offset, size_t bytes)
+{
+       char *kaddr;
+       size_t copied;
+
+       kaddr = kmap(page);
+       if (likely(i->nr_segs == 1)) {
+               int left;
+               char __user *buf = i->iov->iov_base + i->iov_offset;
+               left = copy_to_user(buf, kaddr + offset, bytes);
+               copied = bytes - left;
+       } else {
+               copied = __iovec_copy_to_user(kaddr + offset, i->iov,
+                                             i->iov_offset, bytes, 0);
+       }
+       kunmap(page);
+       return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_to_user);
+
 static size_t __iovec_copy_from_user(char *vaddr, const struct iovec *iov,
                                     size_t base, size_t bytes, int atomic)
 {

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3f40547ba1917cd038f085bcdb6c6e577a9d4538..11647fe75ac6ae0a5611387f7b2ce6f9acd92258 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -297,6 +297,10 @@ struct iov_iter {
        size_t count;
 };
 
+size_t iov_iter_copy_to_user_atomic(struct page *page,
+               struct iov_iter *i, unsigned long offset, size_t bytes);
+size_t iov_iter_copy_to_user(struct page *page,
+               struct iov_iter *i, unsigned long offset, size_t bytes);
 size_t iov_iter_copy_from_user_atomic(struct page *page,
                struct iov_iter *i, unsigned long offset, size_t bytes);
 size_t iov_iter_copy_from_user(struct page *page,