[PATCH 1/1] drivers/vhost : Removes unnecessary 'else' in vhost_copy_from_user

[PATCH 1/1] drivers/vhost : Removes unnecessary 'else' in vhost_copy_from_user

[Leonardo Bras]

There is no need for this else statement, given that if block will return.
This change is not supposed to change the output binary.

It reduces identation level on most lines in this function, and also
fixes an split string on vq_err().

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 drivers/vhost/vhost.c | 50 +++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 26 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f44340b41494..b23d1b74c32f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -824,34 +824,32 @@ static int vhost_copy_from_user(struct vhost_virtqueue *vq, void *to,
 
 	if (!vq->iotlb)
 		return __copy_from_user(to, from, size);
-	else {
-		/* This function should be called after iotlb
-		 * prefetch, which means we're sure that vq
-		 * could be access through iotlb. So -EAGAIN should
-		 * not happen in this case.
-		 */
-		void __user *uaddr = vhost_vq_meta_fetch(vq,
-				     (u64)(uintptr_t)from, size,
-				     VHOST_ADDR_DESC);
-		struct iov_iter f;
 
-		if (uaddr)
-			return __copy_from_user(to, uaddr, size);
+	/* This function should be called after iotlb
+	 * prefetch, which means we're sure that vq
+	 * could be access through iotlb. So -EAGAIN should
+	 * not happen in this case.
+	 */
+	void __user *uaddr = vhost_vq_meta_fetch(vq,
+			     (u64)(uintptr_t)from, size,
+			     VHOST_ADDR_DESC);
+	struct iov_iter f;
 
-		ret = translate_desc(vq, (u64)(uintptr_t)from, size, vq->iotlb_iov,
-				     ARRAY_SIZE(vq->iotlb_iov),
-				     VHOST_ACCESS_RO);
-		if (ret < 0) {
-			vq_err(vq, "IOTLB translation failure: uaddr "
-			       "%p size 0x%llx\n", from,
-			       (unsigned long long) size);
-			goto out;
-		}
-		iov_iter_init(&f, READ, vq->iotlb_iov, ret, size);
-		ret = copy_from_iter(to, size, &f);
-		if (ret == size)
-			ret = 0;
-	}
+	if (uaddr)
+		return __copy_from_user(to, uaddr, size);
+
+	ret = translate_desc(vq, (u64)(uintptr_t)from, size, vq->iotlb_iov,
+			     ARRAY_SIZE(vq->iotlb_iov),
+			     VHOST_ACCESS_RO);
+	if (ret < 0) {
+		vq_err(vq, "IOTLB translation failure: uaddr %p size 0x%llx\n",
+		       from, (unsigned long long)size);
+		goto out;
+	}
+	iov_iter_init(&f, READ, vq->iotlb_iov, ret, size);
+	ret = copy_from_iter(to, size, &f);
+	if (ret == size)
+		ret = 0;
 
 out:
 	return ret;
-- 
2.23.0

Re: [PATCH 1/1] drivers/vhost : Removes unnecessary 'else' in vhost_copy_from_user

[Jason Wang]

On 2019/12/13 上午5:15, Leonardo Bras wrote:
> There is no need for this else statement, given that if block will return.
> This change is not supposed to change the output binary.
>
> It reduces identation level on most lines in this function, and also
> fixes an split string on vq_err().
>
> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> ---
>   drivers/vhost/vhost.c | 50 +++++++++++++++++++++----------------------
>   1 file changed, 24 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f44340b41494..b23d1b74c32f 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -824,34 +824,32 @@ static int vhost_copy_from_user(struct vhost_virtqueue *vq, void *to,
>   
>   	if (!vq->iotlb)
>   		return __copy_from_user(to, from, size);
> -	else {
> -		/* This function should be called after iotlb
> -		 * prefetch, which means we're sure that vq
> -		 * could be access through iotlb. So -EAGAIN should
> -		 * not happen in this case.
> -		 */
> -		void __user *uaddr = vhost_vq_meta_fetch(vq,
> -				     (u64)(uintptr_t)from, size,
> -				     VHOST_ADDR_DESC);
> -		struct iov_iter f;
>   
> -		if (uaddr)
> -			return __copy_from_user(to, uaddr, size);
> +	/* This function should be called after iotlb
> +	 * prefetch, which means we're sure that vq
> +	 * could be access through iotlb. So -EAGAIN should
> +	 * not happen in this case.
> +	 */
> +	void __user *uaddr = vhost_vq_meta_fetch(vq,
> +			     (u64)(uintptr_t)from, size,
> +			     VHOST_ADDR_DESC);
> +	struct iov_iter f;


I think this will lead at least warnings from compiler.

Generally, I would not bother to make changes like this especially 
consider it will bring troubles when trying to backporting fixes to 
downstream in the future.

There're some more interesting things: e.g current metadata IOTLB 
performance is bad for dynamic mapping since it will be reset each time 
a new updating is coming.

We can optimize this by only reset the metadata IOTLB when the updating 
is for metdata.

Want to try this?

Thanks


>   
> -		ret = translate_desc(vq, (u64)(uintptr_t)from, size, vq->iotlb_iov,
> -				     ARRAY_SIZE(vq->iotlb_iov),
> -				     VHOST_ACCESS_RO);
> -		if (ret < 0) {
> -			vq_err(vq, "IOTLB translation failure: uaddr "
> -			       "%p size 0x%llx\n", from,
> -			       (unsigned long long) size);
> -			goto out;
> -		}
> -		iov_iter_init(&f, READ, vq->iotlb_iov, ret, size);
> -		ret = copy_from_iter(to, size, &f);
> -		if (ret == size)
> -			ret = 0;
> -	}
> +	if (uaddr)
> +		return __copy_from_user(to, uaddr, size);
> +
> +	ret = translate_desc(vq, (u64)(uintptr_t)from, size, vq->iotlb_iov,
> +			     ARRAY_SIZE(vq->iotlb_iov),
> +			     VHOST_ACCESS_RO);
> +	if (ret < 0) {
> +		vq_err(vq, "IOTLB translation failure: uaddr %p size 0x%llx\n",
> +		       from, (unsigned long long)size);
> +		goto out;
> +	}
> +	iov_iter_init(&f, READ, vq->iotlb_iov, ret, size);
> +	ret = copy_from_iter(to, size, &f);
> +	if (ret == size)
> +		ret = 0;
>   
>   out:
>   	return ret;