net: skb_copy_datagram_const_iovec()

There's an skb_copy_datagram_iovec() to copy out of a paged skb,
but it modifies the iovec, and does not support starting
at an offset in the destination. We want both in tun.c, so let's
add the function.

It's a carbon copy of skb_copy_datagram_iovec() with enough changes to
be annoying.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 0 deletions

diff --git a/net/core/iovec.c b/net/core/iovec.c
index 4c9c0121c9da..a215545c0a34 100644
--- a/net/core/iovec.c
+++ b/net/core/iovec.c
@@ -98,6 +98,31 @@ int memcpy_toiovec(struct iovec *iov, unsigned char *kdata, int len)
 }
 
 /*
+ *      Copy kernel to iovec. Returns -EFAULT on error.
+ */
+
+int memcpy_toiovecend(const struct iovec *iov, unsigned char *kdata,
+                      int offset, int len)
+{
+        int copy;
+        for (; len > 0; ++iov) {
+                /* Skip over the finished iovecs */
+                if (unlikely(offset >= iov->iov_len)) {
+                        offset -= iov->iov_len;
+                        continue;
+                }
+                copy = min_t(unsigned int, iov->iov_len - offset, len);
+                offset = 0;
+                if (copy_to_user(iov->iov_base, kdata, copy))
+                        return -EFAULT;
+                kdata += copy;
+                len -= copy;
+        }
+
+        return 0;
+}
+
+/*
  *      Copy iovec to kernel. Returns -EFAULT on error.
  *
  *      Note: this modifies the original iovec.
@@ -236,3 +261,4 @@ EXPORT_SYMBOL(csum_partial_copy_fromiovecend);
 EXPORT_SYMBOL(memcpy_fromiovec);
 EXPORT_SYMBOL(memcpy_fromiovecend);
 EXPORT_SYMBOL(memcpy_toiovec);
+EXPORT_SYMBOL(memcpy_toiovecend);