[iov_iter] new primitives - copy_from_iter_full() and friends

copy_from_iter_full(), copy_from_iter_full_nocache() and
csum_and_copy_from_iter_full() - counterparts of copy_from_iter()
et.al., advancing iterator only in case of successful full copy
and returning whether it had been successful or not.

Convert some obvious users.  *NOTE* - do not blindly assume that
something is a good candidate for those unless you are sure that
not advancing iov_iter in failure case is the right thing in
this case.  Anything that does short read/short write kind of
stuff (or is in a loop, etc.) is unlikely to be a good one.

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

1 files changed, 1 insertions, 3 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 070e3290aa6e..19d81ca3fb49 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -673,7 +673,6 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
         int depth;
         bool zerocopy = false;
         size_t linear;
-        ssize_t n;
 
         if (q->flags & IFF_VNET_HDR) {
                 vnet_hdr_len = q->vnet_hdr_sz;
@@ -684,8 +683,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
                 len -= vnet_hdr_len;
 
                 err = -EFAULT;
-                n = copy_from_iter(&vnet_hdr, sizeof(vnet_hdr), from);
-                if (n != sizeof(vnet_hdr))
+                if (!copy_from_iter_full(&vnet_hdr, sizeof(vnet_hdr), from))
                         goto err;
                 iov_iter_advance(from, vnet_hdr_len - sizeof(vnet_hdr));
                 if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&