switch memcpy_to_msg() and skb_copy{,_and_csum}_datagram_msg() to primitives

... making both non-draining.  That means that tcp_recvmsg() becomes
non-draining.  And _that_ would break iscsit_do_rx_data() unless we
	a) make sure tcp_recvmsg() is uniformly non-draining (it is)
	b) make sure it copes with arbitrary (including shifted)
iov_iter (it does, all it uses is iov_iter primitives)
	c) make iscsit_do_rx_data() initialize ->msg_iter only once.

Fortunately, (c) is doable with minimal work and we are rid of one
the two places where kernel send/recvmsg users would be unhappy with
non-draining behaviour.

Actually, that makes all but one of ->recvmsg() instances iov_iter-clean.
The exception is skcipher_recvmsg() and it also isn't hard to convert
to primitives (iov_iter_get_pages() is needed there).  That'll wait
a bit - there's some interplay with ->sendmsg() path for that one.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 28 insertions, 54 deletions

diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index ce87ce9bdb9c..7c6a95bcb35e 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/drivers/target/iscsi/iscsi_target_util.c
@@ -1326,21 +1326,19 @@ static int iscsit_do_rx_data(
         struct iscsi_conn *conn,
         struct iscsi_data_count *count)
 {
-        int data = count->data_length, rx_loop = 0, total_rx = 0, iov_len;
-        struct kvec *iov_p;
+        int data = count->data_length, rx_loop = 0, total_rx = 0;
         struct msghdr msg;
 
         if (!conn || !conn->sock || !conn->conn_ops)
                 return -1;
 
         memset(&msg, 0, sizeof(struct msghdr));
-
-        iov_p = count->iov;
-        iov_len = count->iov_count;
+        iov_iter_kvec(&msg.msg_iter, READ | ITER_KVEC,
+                      count->iov, count->iov_count, data);
 
         while (total_rx < data) {
-                rx_loop = kernel_recvmsg(conn->sock, &msg, iov_p, iov_len,
-                                        (data - total_rx), MSG_WAITALL);
+                rx_loop = sock_recvmsg(conn->sock, &msg,
+                                      (data - total_rx), MSG_WAITALL);
                 if (rx_loop <= 0) {
                         pr_debug("rx_loop: %d total_rx: %d\n",
                                 rx_loop, total_rx);
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 52cf1bdac0d8..4902f2df90c8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2651,17 +2651,10 @@ int skb_copy_datagram_iter(const struct sk_buff *from, int offset,
 static inline int skb_copy_datagram_msg(const struct sk_buff *from, int offset,
                                         struct msghdr *msg, int size)
 {
-        /* XXX: stripping const */
-        return skb_copy_datagram_iovec(from, offset, (struct iovec *)msg->msg_iter.iov, size);
-}
-int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb, int hlen,
-                                     struct iovec *iov);
-static inline int skb_copy_and_csum_datagram_msg(struct sk_buff *skb, int hlen,
-                            struct msghdr *msg)
-{
-        /* XXX: stripping const */
-        return skb_copy_and_csum_datagram_iovec(skb, hlen, (struct iovec *)msg->msg_iter.iov);
+        return skb_copy_datagram_iter(from, offset, &msg->msg_iter, size);
 }
+int skb_copy_and_csum_datagram_msg(struct sk_buff *skb, int hlen,
+                                   struct msghdr *msg);
 int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
                                  struct iov_iter *from, int len);
 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
@@ -2697,8 +2690,7 @@ static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
 
 static inline int memcpy_to_msg(struct msghdr *msg, void *data, int len)
 {
-        /* XXX: stripping const */
-        return memcpy_toiovec((struct iovec *)msg->msg_iter.iov, data, len);
+        return copy_to_iter(data, len, &msg->msg_iter) == len ? 0 : -EFAULT;
 }
 
 struct skb_checksum_ops {
diff --git a/net/core/datagram.c b/net/core/datagram.c
index b6e303b0f01f..41075ed6bb52 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -615,27 +615,25 @@ int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
 EXPORT_SYMBOL(zerocopy_sg_from_iter);
 
 static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
-                                      u8 __user *to, int len,
+                                      struct iov_iter *to, int len,
                                       __wsum *csump)
 {
         int start = skb_headlen(skb);
         int i, copy = start - offset;
         struct sk_buff *frag_iter;
         int pos = 0;
+        int n;
 
         /* Copy header. */
         if (copy > 0) {
-                int err = 0;
                 if (copy > len)
                         copy = len;
-                *csump = csum_and_copy_to_user(skb->data + offset, to, copy,
-                                               *csump, &err);
-                if (err)
+                n = csum_and_copy_to_iter(skb->data + offset, copy, csump, to);
+                if (n != copy)
                         goto fault;
                 if ((len -= copy) == 0)
                         return 0;
                 offset += copy;
-                to += copy;
                 pos = copy;
         }
 
@@ -647,26 +645,22 @@ static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
 
                 end = start + skb_frag_size(frag);
                 if ((copy = end - offset) > 0) {
-                        __wsum csum2;
-                        int err = 0;
-                        u8  *vaddr;
+                        __wsum csum2 = 0;
                         struct page *page = skb_frag_page(frag);
+                        u8  *vaddr = kmap(page);
 
                         if (copy > len)
                                 copy = len;
-                        vaddr = kmap(page);
-                        csum2 = csum_and_copy_to_user(vaddr +
-                                                        frag->page_offset +
-                                                        offset - start,
-                                                      to, copy, 0, &err);
+                        n = csum_and_copy_to_iter(vaddr + frag->page_offset +
+                                                  offset - start, copy,
+                                                  &csum2, to);
                         kunmap(page);
-                        if (err)
+                        if (n != copy)
                                 goto fault;
                         *csump = csum_block_add(*csump, csum2, pos);
                         if (!(len -= copy))
                                 return 0;
                         offset += copy;
-                        to += copy;
                         pos += copy;
                 }
                 start = end;
@@ -691,7 +685,6 @@ static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
                         if ((len -= copy) == 0)
                                 return 0;
                         offset += copy;
-                        to += copy;
                         pos += copy;
                 }
                 start = end;
@@ -744,20 +737,19 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb)
 EXPORT_SYMBOL(__skb_checksum_complete);
 
 /**
- *      skb_copy_and_csum_datagram_iovec - Copy and checksum skb to user iovec.
+ *      skb_copy_and_csum_datagram_msg - Copy and checksum skb to user iovec.
  *      @skb: skbuff
  *      @hlen: hardware length
- *      @iov: io vector
+ *      @msg: destination
  *
  *      Caller _must_ check that skb will fit to this iovec.
  *
  *      Returns: 0       - success.
  *               -EINVAL - checksum failure.
- *               -EFAULT - fault during copy. Beware, in this case iovec
- *                         can be modified!
+ *               -EFAULT - fault during copy.
  */
-int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
-                                     int hlen, struct iovec *iov)
+int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
+                                   int hlen, struct msghdr *msg)
 {
         __wsum csum;
         int chunk = skb->len - hlen;
@@ -765,28 +757,20 @@ int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
         if (!chunk)
                 return 0;
 
-        /* Skip filled elements.
-         * Pretty silly, look at memcpy_toiovec, though 8)
-         */
-        while (!iov->iov_len)
-                iov++;
-
-        if (iov->iov_len < chunk) {
+        if (iov_iter_count(&msg->msg_iter) < chunk) {
                 if (__skb_checksum_complete(skb))
                         goto csum_error;
-                if (skb_copy_datagram_iovec(skb, hlen, iov, chunk))
+                if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
                         goto fault;
         } else {
                 csum = csum_partial(skb->data, hlen, skb->csum);
-                if (skb_copy_and_csum_datagram(skb, hlen, iov->iov_base,
+                if (skb_copy_and_csum_datagram(skb, hlen, &msg->msg_iter,
                                                chunk, &csum))
                         goto fault;
                 if (csum_fold(csum))
                         goto csum_error;
                 if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
                         netdev_rx_csum_fault(skb->dev);
-                iov->iov_len -= chunk;
-                iov->iov_base += chunk;
         }
         return 0;
 csum_error:
@@ -794,7 +778,7 @@ csum_error:
 fault:
         return -EFAULT;
 }
-EXPORT_SYMBOL(skb_copy_and_csum_datagram_iovec);
+EXPORT_SYMBOL(skb_copy_and_csum_datagram_msg);
 
 /**
  *      datagram_poll - generic datagram poll