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-rw-r--r--lib/iov_iter.c36
1 files changed, 36 insertions, 0 deletions
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f2d50d69a6c3..755c10c5138c 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1972,3 +1972,39 @@ int import_single_range(int rw, void __user *buf, size_t len,
return 0;
}
EXPORT_SYMBOL(import_single_range);
+
+/**
+ * iov_iter_restore() - Restore a &struct iov_iter to the same state as when
+ * iov_iter_save_state() was called.
+ *
+ * @i: &struct iov_iter to restore
+ * @state: state to restore from
+ *
+ * Used after iov_iter_save_state() to bring restore @i, if operations may
+ * have advanced it.
+ *
+ * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC
+ */
+void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
+{
+ if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) &&
+ !iov_iter_is_kvec(i))
+ return;
+ i->iov_offset = state->iov_offset;
+ i->count = state->count;
+ /*
+ * For the *vec iters, nr_segs + iov is constant - if we increment
+ * the vec, then we also decrement the nr_segs count. Hence we don't
+ * need to track both of these, just one is enough and we can deduct
+ * the other from that. ITER_KVEC and ITER_IOVEC are the same struct
+ * size, so we can just increment the iov pointer as they are unionzed.
+ * ITER_BVEC _may_ be the same size on some archs, but on others it is
+ * not. Be safe and handle it separately.
+ */
+ BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
+ if (iov_iter_is_bvec(i))
+ i->bvec -= state->nr_segs - i->nr_segs;
+ else
+ i->iov -= state->nr_segs - i->nr_segs;
+ i->nr_segs = state->nr_segs;
+}