+/*
+ * 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_from_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, KM_USER0);
+ if (likely(i->nr_segs == 1)) {
+ int left;
+ char __user *buf = i->iov->iov_base + i->iov_offset;
+ left = __copy_from_user_inatomic_nocache(kaddr + offset,
+ buf, bytes);
+ copied = bytes - left;
+ } else {
+ copied = __iovec_copy_from_user_inatomic(kaddr + offset,
+ i->iov, i->iov_offset, bytes);
+ }
+ kunmap_atomic(kaddr, KM_USER0);
+
+ return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
+
+/*
+ * This has the same sideeffects and return value as
+ * iov_iter_copy_from_user_atomic().
+ * The difference is that it attempts to resolve faults.
+ * Page must not be locked.
+ */
+size_t iov_iter_copy_from_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_from_user_nocache(kaddr + offset, buf, bytes);
+ copied = bytes - left;
+ } else {
+ copied = __iovec_copy_from_user_inatomic(kaddr + offset,
+ i->iov, i->iov_offset, bytes);
+ }
+ kunmap(page);
+ return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_from_user);
+
+static void __iov_iter_advance_iov(struct iov_iter *i, size_t bytes)
+{
+ if (likely(i->nr_segs == 1)) {
+ i->iov_offset += bytes;
+ } else {
+ const struct iovec *iov = i->iov;
+ size_t base = i->iov_offset;
+
+ while (bytes) {
+ int copy = min(bytes, iov->iov_len - base);
+
+ bytes -= copy;
+ base += copy;
+ if (iov->iov_len == base) {
+ iov++;
+ base = 0;
+ }
+ }
+ i->iov = iov;
+ i->iov_offset = base;
+ }
+}
+
+void iov_iter_advance(struct iov_iter *i, size_t bytes)
+{
+ BUG_ON(i->count < bytes);
+
+ __iov_iter_advance_iov(i, bytes);
+ i->count -= bytes;
+}
+EXPORT_SYMBOL(iov_iter_advance);
+
+/*
+ * Fault in the first iovec of the given iov_iter, to a maximum length
+ * of bytes. Returns 0 on success, or non-zero if the memory could not be
+ * accessed (ie. because it is an invalid address).
+ *
+ * writev-intensive code may want this to prefault several iovecs -- that
+ * would be possible (callers must not rely on the fact that _only_ the
+ * first iovec will be faulted with the current implementation).
+ */
+int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
+{
+ char __user *buf = i->iov->iov_base + i->iov_offset;
+ bytes = min(bytes, i->iov->iov_len - i->iov_offset);
+ return fault_in_pages_readable(buf, bytes);
+}
+EXPORT_SYMBOL(iov_iter_fault_in_readable);
+
+/*
+ * Return the count of just the current iov_iter segment.
+ */
+size_t iov_iter_single_seg_count(struct iov_iter *i)
+{
+ const struct iovec *iov = i->iov;
+ if (i->nr_segs == 1)
+ return i->count;
+ else
+ return min(i->count, iov->iov_len - i->iov_offset);
+}
+EXPORT_SYMBOL(iov_iter_single_seg_count);
+