Patchwork [V8,2/4,net-next] skbuff: skb supports zero-copy buffers

login
register
mail settings
Submitter Shirley Ma
Date July 6, 2011, 10:22 p.m.
Message ID <1309990932.10209.19.camel@localhost.localdomain>
Download mbox | patch
Permalink /patch/103585/
State Accepted
Delegated to: David Miller
Headers show

Comments

Shirley Ma - July 6, 2011, 10:22 p.m.
This patch adds userspace buffers support in skb shared info. A new 
struct skb_ubuf_info is needed to maintain the userspace buffers
argument and index, a callback is used to notify userspace to release
the buffers once lower device has done DMA (Last reference to that skb
has gone).

If there is any userspace apps to reference these userspace buffers,
then these userspaces buffers will be copied into kernel. This way we
can prevent userspace apps from holding these userspace buffers too long.

Use destructor_arg to point to the userspace buffer info; a new tx flags
SKBTX_DEV_ZEROCOPY is added for zero-copy buffer check.

Signed-off-by: Shirley Ma <xma@...ibm.com>
---

 include/linux/skbuff.h |   16 ++++++++++
 net/core/skbuff.c      |   79 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 94 insertions(+), 1 deletions(-)



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Zan Lynx - July 6, 2011, 11:01 p.m.
On 7/6/2011 4:22 PM, Shirley Ma wrote:
> This patch adds userspace buffers support in skb shared info. A new 
> struct skb_ubuf_info is needed to maintain the userspace buffers
> argument and index, a callback is used to notify userspace to release
> the buffers once lower device has done DMA (Last reference to that skb
> has gone).
> 
> If there is any userspace apps to reference these userspace buffers,
> then these userspaces buffers will be copied into kernel. This way we
> can prevent userspace apps from holding these userspace buffers too long.
> 
> Use destructor_arg to point to the userspace buffer info; a new tx flags
> SKBTX_DEV_ZEROCOPY is added for zero-copy buffer check.
> 
> Signed-off-by: Shirley Ma <xma@...ibm.com>

I was just reading this patch and noticed that you check if
uarg->callback is set before calling it in skb_release_data, but you do
not check before calling it in skb_copy_ubufs.

I was only skimming so I have probably missed something...

> ---
> 
>  include/linux/skbuff.h |   16 ++++++++++
>  net/core/skbuff.c      |   79 +++++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 94 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 3e54337..08d4507 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -187,6 +187,20 @@ enum {
>  
>  	/* ensure the originating sk reference is available on driver level */
>  	SKBTX_DRV_NEEDS_SK_REF = 1 << 3,
> +
> +	/* device driver supports TX zero-copy buffers */
> +	SKBTX_DEV_ZEROCOPY = 1 << 4,
> +};
> +
> +/*
> + * The callback notifies userspace to release buffers when skb DMA is done in
> + * lower device, the skb last reference should be 0 when calling this.
> + * The desc is used to track userspace buffer index.
> + */
> +struct ubuf_info {
> +	void (*callback)(void *);
> +	void *arg;
> +	unsigned long desc;
>  };
>  
>  /* This data is invariant across clones and lives at
> @@ -211,6 +225,7 @@ struct skb_shared_info {
>  	/* Intermediate layers must ensure that destructor_arg
>  	 * remains valid until skb destructor */
>  	void *		destructor_arg;
> +
>  	/* must be last field, see pskb_expand_head() */
>  	skb_frag_t	frags[MAX_SKB_FRAGS];
>  };
> @@ -2265,5 +2280,6 @@ static inline void skb_checksum_none_assert(struct sk_buff *skb)
>  }
>  
>  bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
> +
>  #endif	/* __KERNEL__ */
>  #endif	/* _LINUX_SKBUFF_H */
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 46cbd28..42462f5 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -329,6 +329,18 @@ static void skb_release_data(struct sk_buff *skb)
>  				put_page(skb_shinfo(skb)->frags[i].page);
>  		}
>  
> +		/*
> +		 * If skb buf is from userspace, we need to notify the caller
> +		 * the lower device DMA has done;
> +		 */
> +		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
> +			struct ubuf_info *uarg;
> +
> +			uarg = skb_shinfo(skb)->destructor_arg;
> +			if (uarg->callback)
> +				uarg->callback(uarg);
> +		}
> +
>  		if (skb_has_frag_list(skb))
>  			skb_drop_fraglist(skb);
>  
> @@ -481,6 +493,9 @@ bool skb_recycle_check(struct sk_buff *skb, int skb_size)
>  	if (irqs_disabled())
>  		return false;
>  
> +	if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY)
> +		return false;
> +
>  	if (skb_is_nonlinear(skb) || skb->fclone != SKB_FCLONE_UNAVAILABLE)
>  		return false;
>  
> @@ -596,6 +611,50 @@ struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
>  }
>  EXPORT_SYMBOL_GPL(skb_morph);
>  
> +/* skb frags copy userspace buffers to kernel */
> +static int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
> +{
> +	int i;
> +	int num_frags = skb_shinfo(skb)->nr_frags;
> +	struct page *page, *head = NULL;
> +	struct ubuf_info *uarg = skb_shinfo(skb)->destructor_arg;
> +
> +	for (i = 0; i < num_frags; i++) {
> +		u8 *vaddr;
> +		skb_frag_t *f = &skb_shinfo(skb)->frags[i];
> +
> +		page = alloc_page(GFP_ATOMIC);
> +		if (!page) {
> +			while (head) {
> +				put_page(head);
> +				head = (struct page *)head->private;
> +			}
> +			return -ENOMEM;
> +		}
> +		vaddr = kmap_skb_frag(&skb_shinfo(skb)->frags[i]);
> +		memcpy(page_address(page),
> +		       vaddr + f->page_offset, f->size);
> +		kunmap_skb_frag(vaddr);
> +		page->private = (unsigned long)head;
> +		head = page;
> +	}
> +
> +	/* skb frags release userspace buffers */
> +	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
> +		put_page(skb_shinfo(skb)->frags[i].page);
> +
> +	uarg->callback(uarg);
> +
> +	/* skb frags point to kernel buffers */
> +	for (i = skb_shinfo(skb)->nr_frags; i > 0; i--) {
> +		skb_shinfo(skb)->frags[i - 1].page_offset = 0;
> +		skb_shinfo(skb)->frags[i - 1].page = head;
> +		head = (struct page *)head->private;
> +	}
> +	return 0;
> +}
> +
> +
>  /**
>   *	skb_clone	-	duplicate an sk_buff
>   *	@skb: buffer to clone
> @@ -614,6 +673,11 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
>  {
>  	struct sk_buff *n;
>  
> +	if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
> +		if (skb_copy_ubufs(skb, gfp_mask))
> +			return NULL;
> +	}
> +
>  	n = skb + 1;
>  	if (skb->fclone == SKB_FCLONE_ORIG &&
>  	    n->fclone == SKB_FCLONE_UNAVAILABLE) {
> @@ -731,6 +795,12 @@ struct sk_buff *pskb_copy(struct sk_buff *skb, gfp_t gfp_mask)
>  	if (skb_shinfo(skb)->nr_frags) {
>  		int i;
>  
> +		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
> +			if (skb_copy_ubufs(skb, gfp_mask)) {
> +				kfree(n);
> +				goto out;
> +			}
> +		}
>  		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
>  			skb_shinfo(n)->frags[i] = skb_shinfo(skb)->frags[i];
>  			get_page(skb_shinfo(n)->frags[i].page);
> @@ -788,7 +858,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
>  		fastpath = true;
>  	else {
>  		int delta = skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1;
> -
>  		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
>  	}
>  
> @@ -819,6 +888,11 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
>  	if (fastpath) {
>  		kfree(skb->head);
>  	} else {
> +		/* copy this zero copy skb frags */
> +		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
> +			if (skb_copy_ubufs(skb, gfp_mask))
> +				goto nofrags;
> +		}
>  		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
>  			get_page(skb_shinfo(skb)->frags[i].page);
>  
> @@ -853,6 +927,8 @@ adjust_others:
>  	atomic_set(&skb_shinfo(skb)->dataref, 1);
>  	return 0;
>  
> +nofrags:
> +	kfree(data);
>  nodata:
>  	return -ENOMEM;
>  }
> @@ -1354,6 +1430,7 @@ int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
>  		}
>  		start = end;
>  	}
> +
>  	if (!len)
>  		return 0;
>  
> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Shirley Ma - July 6, 2011, 11:24 p.m.
On Wed, 2011-07-06 at 17:01 -0600, Zan Lynx wrote:
> On 7/6/2011 4:22 PM, Shirley Ma wrote:
> > This patch adds userspace buffers support in skb shared info. A new 
> > struct skb_ubuf_info is needed to maintain the userspace buffers
> > argument and index, a callback is used to notify userspace to
> release
> > the buffers once lower device has done DMA (Last reference to that
> skb
> > has gone).
> > 
> > If there is any userspace apps to reference these userspace buffers,
> > then these userspaces buffers will be copied into kernel. This way
> we
> > can prevent userspace apps from holding these userspace buffers too
> long.
> > 
> > Use destructor_arg to point to the userspace buffer info; a new tx
> flags
> > SKBTX_DEV_ZEROCOPY is added for zero-copy buffer check.
> > 
> > Signed-off-by: Shirley Ma <xma@...ibm.com>
> 
> I was just reading this patch and noticed that you check if
> uarg->callback is set before calling it in skb_release_data, but you
> do
> not check before calling it in skb_copy_ubufs.
> 
> I was only skimming so I have probably missed something...

It is a redundant check. The userspace buffer info always has a callback
to release the buffers. I should have removed it after using tx_flags.

Thanks
Shirley

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
David Miller - July 7, 2011, 11:01 a.m.
From: Shirley Ma <mashirle@us.ibm.com>
Date: Wed, 06 Jul 2011 15:22:12 -0700

> +			while (head) {
> +				put_page(head);
> +				head = (struct page *)head->private;
> +			}

Looks like you might be referencing the page after it's
release here.  I think you need something like:

			while (head) {
				struct page *next = (struct page *)head->private;
				put_page(head);
				head = next;
			}
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Shirley Ma - July 7, 2011, 6:32 p.m.
On Thu, 2011-07-07 at 04:01 -0700, David Miller wrote:
> From: Shirley Ma <mashirle@us.ibm.com>
> Date: Wed, 06 Jul 2011 15:22:12 -0700
> 
> > +                     while (head) {
> > +                             put_page(head);
> > +                             head = (struct page *)head->private;
> > +                     }
> 
> Looks like you might be referencing the page after it's
> release here.  I think you need something like:
> 
>                         while (head) {
>                                 struct page *next = (struct page
> *)head->private;
>                                 put_page(head);
>                                 head = next;
>                         }
> --

You are right, will fix it.

Thanks
Shirley
 

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
David Miller - July 7, 2011, 6:39 p.m.
From: Shirley Ma <mashirle@us.ibm.com>
Date: Thu, 07 Jul 2011 11:32:25 -0700

> You are right, will fix it.

You don't need to, I fixed it when I committed the patch
to net-next-2.6
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3e54337..08d4507 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -187,6 +187,20 @@  enum {
 
 	/* ensure the originating sk reference is available on driver level */
 	SKBTX_DRV_NEEDS_SK_REF = 1 << 3,
+
+	/* device driver supports TX zero-copy buffers */
+	SKBTX_DEV_ZEROCOPY = 1 << 4,
+};
+
+/*
+ * The callback notifies userspace to release buffers when skb DMA is done in
+ * lower device, the skb last reference should be 0 when calling this.
+ * The desc is used to track userspace buffer index.
+ */
+struct ubuf_info {
+	void (*callback)(void *);
+	void *arg;
+	unsigned long desc;
 };
 
 /* This data is invariant across clones and lives at
@@ -211,6 +225,7 @@  struct skb_shared_info {
 	/* Intermediate layers must ensure that destructor_arg
 	 * remains valid until skb destructor */
 	void *		destructor_arg;
+
 	/* must be last field, see pskb_expand_head() */
 	skb_frag_t	frags[MAX_SKB_FRAGS];
 };
@@ -2265,5 +2280,6 @@  static inline void skb_checksum_none_assert(struct sk_buff *skb)
 }
 
 bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 46cbd28..42462f5 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -329,6 +329,18 @@  static void skb_release_data(struct sk_buff *skb)
 				put_page(skb_shinfo(skb)->frags[i].page);
 		}
 
+		/*
+		 * If skb buf is from userspace, we need to notify the caller
+		 * the lower device DMA has done;
+		 */
+		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
+			struct ubuf_info *uarg;
+
+			uarg = skb_shinfo(skb)->destructor_arg;
+			if (uarg->callback)
+				uarg->callback(uarg);
+		}
+
 		if (skb_has_frag_list(skb))
 			skb_drop_fraglist(skb);
 
@@ -481,6 +493,9 @@  bool skb_recycle_check(struct sk_buff *skb, int skb_size)
 	if (irqs_disabled())
 		return false;
 
+	if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY)
+		return false;
+
 	if (skb_is_nonlinear(skb) || skb->fclone != SKB_FCLONE_UNAVAILABLE)
 		return false;
 
@@ -596,6 +611,50 @@  struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
 }
 EXPORT_SYMBOL_GPL(skb_morph);
 
+/* skb frags copy userspace buffers to kernel */
+static int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
+{
+	int i;
+	int num_frags = skb_shinfo(skb)->nr_frags;
+	struct page *page, *head = NULL;
+	struct ubuf_info *uarg = skb_shinfo(skb)->destructor_arg;
+
+	for (i = 0; i < num_frags; i++) {
+		u8 *vaddr;
+		skb_frag_t *f = &skb_shinfo(skb)->frags[i];
+
+		page = alloc_page(GFP_ATOMIC);
+		if (!page) {
+			while (head) {
+				put_page(head);
+				head = (struct page *)head->private;
+			}
+			return -ENOMEM;
+		}
+		vaddr = kmap_skb_frag(&skb_shinfo(skb)->frags[i]);
+		memcpy(page_address(page),
+		       vaddr + f->page_offset, f->size);
+		kunmap_skb_frag(vaddr);
+		page->private = (unsigned long)head;
+		head = page;
+	}
+
+	/* skb frags release userspace buffers */
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
+		put_page(skb_shinfo(skb)->frags[i].page);
+
+	uarg->callback(uarg);
+
+	/* skb frags point to kernel buffers */
+	for (i = skb_shinfo(skb)->nr_frags; i > 0; i--) {
+		skb_shinfo(skb)->frags[i - 1].page_offset = 0;
+		skb_shinfo(skb)->frags[i - 1].page = head;
+		head = (struct page *)head->private;
+	}
+	return 0;
+}
+
+
 /**
  *	skb_clone	-	duplicate an sk_buff
  *	@skb: buffer to clone
@@ -614,6 +673,11 @@  struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
 {
 	struct sk_buff *n;
 
+	if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
+		if (skb_copy_ubufs(skb, gfp_mask))
+			return NULL;
+	}
+
 	n = skb + 1;
 	if (skb->fclone == SKB_FCLONE_ORIG &&
 	    n->fclone == SKB_FCLONE_UNAVAILABLE) {
@@ -731,6 +795,12 @@  struct sk_buff *pskb_copy(struct sk_buff *skb, gfp_t gfp_mask)
 	if (skb_shinfo(skb)->nr_frags) {
 		int i;
 
+		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
+			if (skb_copy_ubufs(skb, gfp_mask)) {
+				kfree(n);
+				goto out;
+			}
+		}
 		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 			skb_shinfo(n)->frags[i] = skb_shinfo(skb)->frags[i];
 			get_page(skb_shinfo(n)->frags[i].page);
@@ -788,7 +858,6 @@  int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 		fastpath = true;
 	else {
 		int delta = skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1;
-
 		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
 	}
 
@@ -819,6 +888,11 @@  int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 	if (fastpath) {
 		kfree(skb->head);
 	} else {
+		/* copy this zero copy skb frags */
+		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
+			if (skb_copy_ubufs(skb, gfp_mask))
+				goto nofrags;
+		}
 		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
 			get_page(skb_shinfo(skb)->frags[i].page);
 
@@ -853,6 +927,8 @@  adjust_others:
 	atomic_set(&skb_shinfo(skb)->dataref, 1);
 	return 0;
 
+nofrags:
+	kfree(data);
 nodata:
 	return -ENOMEM;
 }
@@ -1354,6 +1430,7 @@  int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
 		}
 		start = end;
 	}
+
 	if (!len)
 		return 0;