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Date:	Mon, 24 Nov 2014 00:27:42 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	David Miller <davem@...emloft.net>, torvalds@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	target-devel@...r.kernel.org, nab@...ux-iscsi.org,
	hch@...radead.org
Subject: Re: [PATCH 08/17] {macvtap,tun}_get_user(): switch to iov_iter

On Sat, 2014-11-22 at 04:33 +0000, Al Viro wrote:
> allows to switch macvtap and tun from ->aio_write() to ->write_iter()
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  drivers/net/macvtap.c |   43 ++++++++++++++++++++-----------------------
>  drivers/net/tun.c     |   43 +++++++++++++++++++++++--------------------
>  2 files changed, 43 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index cdd820f..2bf08c6 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -640,12 +640,12 @@ static void macvtap_skb_to_vnet_hdr(const struct sk_buff *skb,
>  
>  /* Get packet from user space buffer */
>  static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
> -				const struct iovec *iv, unsigned long total_len,
> -				size_t count, int noblock)
> +				struct iov_iter *from, int noblock)
>  {
>  	int good_linear = SKB_MAX_HEAD(NET_IP_ALIGN);
>  	struct sk_buff *skb;
>  	struct macvlan_dev *vlan;
> +	unsigned long total_len = iov_iter_count(from);
>  	unsigned long len = total_len;
>  	int err;
>  	struct virtio_net_hdr vnet_hdr = { 0 };
> @@ -653,6 +653,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>  	int copylen = 0;
>  	bool zerocopy = false;
>  	size_t linear;
> +	ssize_t n;
>  
>  	if (q->flags & IFF_VNET_HDR) {
>  		vnet_hdr_len = q->vnet_hdr_sz;
> @@ -662,10 +663,11 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>  			goto err;
>  		len -= vnet_hdr_len;
>  
> -		err = memcpy_fromiovecend((void *)&vnet_hdr, iv, 0,
> -					   sizeof(vnet_hdr));
> -		if (err < 0)
> +		err = -EFAULT;
> +		n = copy_from_iter(&vnet_hdr, sizeof(vnet_hdr), from);
> +		if (n != sizeof(vnet_hdr))
>  			goto err;
> +		iov_iter_advance(from, vnet_hdr_len - sizeof(vnet_hdr));
>  		if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
>  		     vnet_hdr.csum_start + vnet_hdr.csum_offset + 2 >
>  							vnet_hdr.hdr_len)
> @@ -680,17 +682,15 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>  	if (unlikely(len < ETH_HLEN))
>  		goto err;
>  
> -	err = -EMSGSIZE;
> -	if (unlikely(count > UIO_MAXIOV))
> -		goto err;
> -
>  	if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
> +		struct iov_iter i;

Blank line needed after a declaration.

>  		copylen = vnet_hdr.hdr_len ? vnet_hdr.hdr_len : GOODCOPY_LEN;
>  		if (copylen > good_linear)
>  			copylen = good_linear;
>  		linear = copylen;
> -		if (iov_pages(iv, vnet_hdr_len + copylen, count)
> -		    <= MAX_SKB_FRAGS)
> +		i = *from;
> +		iov_iter_advance(&i, copylen);
> +		if (iov_iter_npages(&i, INT_MAX) <= MAX_SKB_FRAGS)

The maxpages argument should be MAX_SKB_FRAGS + 1 as we don't need the
exact number.

>  			zerocopy = true;
>  	}
>  
> @@ -708,10 +708,9 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>  		goto err;
>  
>  	if (zerocopy)
> -		err = zerocopy_sg_from_iovec(skb, iv, vnet_hdr_len, count);
> +		err = zerocopy_sg_from_iter(skb, from);
>  	else {
> -		err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len,
> -						   len);
> +		err = skb_copy_datagram_from_iter(skb, 0, from, len);

Does skb_copy_datagram_from_iter() really need a len parameter?  Here it
is equal to iov_iter_count(from).

[...]
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1012,28 +1012,29 @@ static struct sk_buff *tun_alloc_skb(struct tun_file *tfile,
>  
>  /* Get packet from user space buffer */
>  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> -			    void *msg_control, const struct iovec *iv,
> -			    size_t total_len, size_t count, int noblock)
> +			    void *msg_control, struct iov_iter *from,
> +			    int noblock)
>  {
>  	struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
>  	struct sk_buff *skb;
> +	size_t total_len = iov_iter_count(from);
>  	size_t len = total_len, align = NET_SKB_PAD, linear;
>  	struct virtio_net_hdr gso = { 0 };
>  	int good_linear;
> -	int offset = 0;
>  	int copylen;
>  	bool zerocopy = false;
>  	int err;
>  	u32 rxhash;
> +	ssize_t n;
>  
>  	if (!(tun->flags & TUN_NO_PI)) {
>  		if (len < sizeof(pi))
>  			return -EINVAL;
>  		len -= sizeof(pi);
>  
> -		if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
> +		n = copy_from_iter(&pi, sizeof(pi), from);
> +		if (n != sizeof(pi))
>  			return -EFAULT;
> -		offset += sizeof(pi);
>  	}
>  
>  	if (tun->flags & TUN_VNET_HDR) {
> @@ -1041,7 +1042,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  			return -EINVAL;
>  		len -= tun->vnet_hdr_sz;
>  
> -		if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
> +		n = copy_from_iter(&gso, sizeof(gso), from);
> +		if (n != sizeof(gso))
>  			return -EFAULT;
>  
>  		if ((gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
> @@ -1050,7 +1052,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  
>  		if (gso.hdr_len > len)
>  			return -EINVAL;
> -		offset += tun->vnet_hdr_sz;
> +		iov_iter_advance(from, tun->vnet_hdr_sz);

                                        tun->vnet_hdr_sz - sizeof(gso)

>  	}
>  
>  	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
> @@ -1063,6 +1065,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  	good_linear = SKB_MAX_HEAD(align);
>  
>  	if (msg_control) {
> +		struct iov_iter i = *from;

Blank line needed after a declaration.

>  		/* There are 256 bytes to be copied in skb, so there is
>  		 * enough room for skb expand head in case it is used.
>  		 * The rest of the buffer is mapped from userspace.
> @@ -1071,7 +1074,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  		if (copylen > good_linear)
>  			copylen = good_linear;
>  		linear = copylen;
> -		if (iov_pages(iv, offset + copylen, count) <= MAX_SKB_FRAGS)
> +		iov_iter_advance(&i, copylen);
> +		if (iov_iter_npages(&i, INT_MAX) <= MAX_SKB_FRAGS)

Again, the maxpages argument should be MAX_SKB_FRAGS + 1.

>  			zerocopy = true;
>  	}
>  
> @@ -1091,9 +1095,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  	}
>  
>  	if (zerocopy)
> -		err = zerocopy_sg_from_iovec(skb, iv, offset, count);
> +		err = zerocopy_sg_from_iter(skb, from);
>  	else {
> -		err = skb_copy_datagram_from_iovec(skb, 0, iv, offset, len);
> +		err = skb_copy_datagram_from_iter(skb, 0, from, len);
[...]

Again len is equal to iov_iter_count(from), so I think that parameter is
redundant.

Ben.

-- 
Ben Hutchings
Absolutum obsoletum. (If it works, it's out of date.) - Stafford Beer

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