Patchwork xen/netfront: handle compound page fragments on transmit

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Submitter Ian Campbell
Date Nov. 20, 2012, 11:40 a.m.
Message ID <1353411606-15940-1-git-send-email-ian.campbell@citrix.com>
Download mbox | patch
Permalink /patch/200307/
State Superseded
Delegated to: David Miller
Headers show

Comments

Ian Campbell - Nov. 20, 2012, 11:40 a.m.
An SKB paged fragment can consist of a compound page with order > 0.
However the netchannel protocol deals only in PAGE_SIZE frames.

Handle this in xennet_make_frags by iterating over the frames which
make up the page.

This is the netfront equivalent to 6a8ed462f16b for netback.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: netdev@vger.kernel.org
Cc: xen-devel@lists.xen.org
Cc: Eric Dumazet <edumazet@google.com>
Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>
Cc: ANNIE LI <annie.li@oracle.com>
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Cc: Stefan Bader <stefan.bader@canonical.com>
---
 drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
 1 files changed, 44 insertions(+), 14 deletions(-)
Jan Beulich - Nov. 20, 2012, 12:28 p.m.
>>> On 20.11.12 at 12:40, Ian Campbell <ian.campbell@citrix.com> wrote:
> An SKB paged fragment can consist of a compound page with order > 0.
> However the netchannel protocol deals only in PAGE_SIZE frames.
> 
> Handle this in xennet_make_frags by iterating over the frames which
> make up the page.
> 
> This is the netfront equivalent to 6a8ed462f16b for netback.

Wouldn't you need to be at least a little more conservative here
with respect to resource use: I realize that get_id_from_freelist()
return values were never checked, and failure of
gnttab_claim_grant_reference() was always dealt with via
BUG_ON(), but considering that netfront_tx_slot_available()
doesn't account for compound page fragments, I think this (lack
of) error handling needs improvement in the course of the
change here (regardless of - I think - someone having said that
usually the sum of all pages referenced from an skb's fragments
would not exceed MAX_SKB_FRAGS - "usually" just isn't enough
imo).

Jan

> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: netdev@vger.kernel.org 
> Cc: xen-devel@lists.xen.org 
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>
> Cc: ANNIE LI <annie.li@oracle.com>
> Cc: Sander Eikelenboom <linux@eikelenboom.it>
> Cc: Stefan Bader <stefan.bader@canonical.com>
> ---
>  drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>  1 files changed, 44 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..a12b99a 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, 
> struct net_device *dev,
>  	/* Grant backend access to each skb fragment page. */
>  	for (i = 0; i < frags; i++) {
>  		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> +		struct page *page = skb_frag_page(frag);
> +		unsigned long size = skb_frag_size(frag);
> +		unsigned long offset = frag->page_offset;
>  
> -		tx->flags |= XEN_NETTXF_more_data;
> +		/* Data must not cross a page boundary. */
> +		BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>  
> -		id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> -		np->tx_skbs[id].skb = skb_get(skb);
> -		tx = RING_GET_REQUEST(&np->tx, prod++);
> -		tx->id = id;
> -		ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> -		BUG_ON((signed short)ref < 0);
> +		/* Skip unused frames from start of page */
> +		page += offset >> PAGE_SHIFT;
> +		offset &= ~PAGE_MASK;
>  
> -		mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
> -		gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> -						mfn, GNTMAP_readonly);
> +		while (size > 0) {
> +			unsigned long bytes;
>  
> -		tx->gref = np->grant_tx_ref[id] = ref;
> -		tx->offset = frag->page_offset;
> -		tx->size = skb_frag_size(frag);
> -		tx->flags = 0;
> +			BUG_ON(offset >= PAGE_SIZE);
> +
> +			bytes = PAGE_SIZE - offset;
> +			if (bytes > size)
> +				bytes = size;
> +
> +			tx->flags |= XEN_NETTXF_more_data;
> +
> +			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> +			np->tx_skbs[id].skb = skb_get(skb);
> +			tx = RING_GET_REQUEST(&np->tx, prod++);
> +			tx->id = id;
> +			ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> +			BUG_ON((signed short)ref < 0);
> +
> +			mfn = pfn_to_mfn(page_to_pfn(page));
> +			gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> +							mfn, GNTMAP_readonly);
> +
> +			tx->gref = np->grant_tx_ref[id] = ref;
> +			tx->offset = offset;
> +			tx->size = bytes;
> +			tx->flags = 0;
> +
> +			offset += bytes;
> +			size -= bytes;
> +
> +			/* Next frame */
> +			if (offset == PAGE_SIZE && size) {
> +				BUG_ON(!PageCompound(page));
> +				page++;
> +				offset = 0;
> +			}
> +		}
>  	}
>  
>  	np->tx.req_prod_pvt = prod;
> -- 
> 1.7.2.5
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org 
> http://lists.xen.org/xen-devel 


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Stefan Bader - Nov. 20, 2012, 1:30 p.m.
Aside from Jans comments about error handling, I tried below patch and it seems
to solve the problem with transfers out of the domU for me (though only shallow
testing done, otoh 5 times is more than getting stuck the first time).

-Stefan

On 20.11.2012 12:40, Ian Campbell wrote:
> An SKB paged fragment can consist of a compound page with order > 0.
> However the netchannel protocol deals only in PAGE_SIZE frames.
> 
> Handle this in xennet_make_frags by iterating over the frames which
> make up the page.
> 
> This is the netfront equivalent to 6a8ed462f16b for netback.
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: netdev@vger.kernel.org
> Cc: xen-devel@lists.xen.org
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>
> Cc: ANNIE LI <annie.li@oracle.com>
> Cc: Sander Eikelenboom <linux@eikelenboom.it>
> Cc: Stefan Bader <stefan.bader@canonical.com>
Tested-by: Stefan Bader <stefan.bader@canonical.com>
> ---
>  drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>  1 files changed, 44 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..a12b99a 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
>  	/* Grant backend access to each skb fragment page. */
>  	for (i = 0; i < frags; i++) {
>  		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> +		struct page *page = skb_frag_page(frag);
> +		unsigned long size = skb_frag_size(frag);
> +		unsigned long offset = frag->page_offset;
>  
> -		tx->flags |= XEN_NETTXF_more_data;
> +		/* Data must not cross a page boundary. */
> +		BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>  
> -		id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> -		np->tx_skbs[id].skb = skb_get(skb);
> -		tx = RING_GET_REQUEST(&np->tx, prod++);
> -		tx->id = id;
> -		ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> -		BUG_ON((signed short)ref < 0);
> +		/* Skip unused frames from start of page */
> +		page += offset >> PAGE_SHIFT;
> +		offset &= ~PAGE_MASK;
>  
> -		mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
> -		gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> -						mfn, GNTMAP_readonly);
> +		while (size > 0) {
> +			unsigned long bytes;
>  
> -		tx->gref = np->grant_tx_ref[id] = ref;
> -		tx->offset = frag->page_offset;
> -		tx->size = skb_frag_size(frag);
> -		tx->flags = 0;
> +			BUG_ON(offset >= PAGE_SIZE);
> +
> +			bytes = PAGE_SIZE - offset;
> +			if (bytes > size)
> +				bytes = size;
> +
> +			tx->flags |= XEN_NETTXF_more_data;
> +
> +			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> +			np->tx_skbs[id].skb = skb_get(skb);
> +			tx = RING_GET_REQUEST(&np->tx, prod++);
> +			tx->id = id;
> +			ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> +			BUG_ON((signed short)ref < 0);
> +
> +			mfn = pfn_to_mfn(page_to_pfn(page));
> +			gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> +							mfn, GNTMAP_readonly);
> +
> +			tx->gref = np->grant_tx_ref[id] = ref;
> +			tx->offset = offset;
> +			tx->size = bytes;
> +			tx->flags = 0;
> +
> +			offset += bytes;
> +			size -= bytes;
> +
> +			/* Next frame */
> +			if (offset == PAGE_SIZE && size) {
> +				BUG_ON(!PageCompound(page));
> +				page++;
> +				offset = 0;
> +			}
> +		}
>  	}
>  
>  	np->tx.req_prod_pvt = prod;
>
Sander Eikelenboom - Nov. 20, 2012, 1:45 p.m.
Tuesday, November 20, 2012, 2:30:54 PM, you wrote:

> Aside from Jans comments about error handling, I tried below patch and it seems
> to solve the problem with transfers out of the domU for me (though only shallow
> testing done, otoh 5 times is more than getting stuck the first time).

> -Stefan

I'm running with this patch now, it seems to fix the problems for me as well.

--
Sander

> On 20.11.2012 12:40, Ian Campbell wrote:
>> An SKB paged fragment can consist of a compound page with order > 0.
>> However the netchannel protocol deals only in PAGE_SIZE frames.
>> 
>> Handle this in xennet_make_frags by iterating over the frames which
>> make up the page.
>> 
>> This is the netfront equivalent to 6a8ed462f16b for netback.
>> 
>> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
>> Cc: netdev@vger.kernel.org
>> Cc: xen-devel@lists.xen.org
>> Cc: Eric Dumazet <edumazet@google.com>
>> Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>
>> Cc: ANNIE LI <annie.li@oracle.com>
>> Cc: Sander Eikelenboom <linux@eikelenboom.it>
>> Cc: Stefan Bader <stefan.bader@canonical.com>
> Tested-by: Stefan Bader <stefan.bader@canonical.com>
>> ---
>>  drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>>  1 files changed, 44 insertions(+), 14 deletions(-)
>> 
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index caa0110..a12b99a 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
>>       /* Grant backend access to each skb fragment page. */
>>       for (i = 0; i < frags; i++) {
>>               skb_frag_t *frag = skb_shinfo(skb)->frags + i;
>> +             struct page *page = skb_frag_page(frag);
>> +             unsigned long size = skb_frag_size(frag);
>> +             unsigned long offset = frag->page_offset;
>>  
>> -             tx->flags |= XEN_NETTXF_more_data;
>> +             /* Data must not cross a page boundary. */
>> +             BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>>  
>> -             id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
>> -             np->tx_skbs[id].skb = skb_get(skb);
>> -             tx = RING_GET_REQUEST(&np->tx, prod++);
>> -             tx->id = id;
>> -             ref = gnttab_claim_grant_reference(&np->gref_tx_head);
>> -             BUG_ON((signed short)ref < 0);
>> +             /* Skip unused frames from start of page */
>> +             page += offset >> PAGE_SHIFT;
>> +             offset &= ~PAGE_MASK;
>>  
>> -             mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
>> -             gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
>> -                                             mfn, GNTMAP_readonly);
>> +             while (size > 0) {
>> +                     unsigned long bytes;
>>  
>> -             tx->gref = np->grant_tx_ref[id] = ref;
>> -             tx->offset = frag->page_offset;
>> -             tx->size = skb_frag_size(frag);
>> -             tx->flags = 0;
>> +                     BUG_ON(offset >= PAGE_SIZE);
>> +
>> +                     bytes = PAGE_SIZE - offset;
>> +                     if (bytes > size)
>> +                             bytes = size;
>> +
>> +                     tx->flags |= XEN_NETTXF_more_data;
>> +
>> +                     id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
>> +                     np->tx_skbs[id].skb = skb_get(skb);
>> +                     tx = RING_GET_REQUEST(&np->tx, prod++);
>> +                     tx->id = id;
>> +                     ref = gnttab_claim_grant_reference(&np->gref_tx_head);
>> +                     BUG_ON((signed short)ref < 0);
>> +
>> +                     mfn = pfn_to_mfn(page_to_pfn(page));
>> +                     gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
>> +                                                     mfn, GNTMAP_readonly);
>> +
>> +                     tx->gref = np->grant_tx_ref[id] = ref;
>> +                     tx->offset = offset;
>> +                     tx->size = bytes;
>> +                     tx->flags = 0;
>> +
>> +                     offset += bytes;
>> +                     size -= bytes;
>> +
>> +                     /* Next frame */
>> +                     if (offset == PAGE_SIZE && size) {
>> +                             BUG_ON(!PageCompound(page));
>> +                             page++;
>> +                             offset = 0;
>> +                     }
>> +             }
>>       }
>>  
>>       np->tx.req_prod_pvt = prod;
>> 



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Eric Dumazet - Nov. 20, 2012, 2:45 p.m.
On Tue, 2012-11-20 at 11:40 +0000, Ian Campbell wrote:
> An SKB paged fragment can consist of a compound page with order > 0.
> However the netchannel protocol deals only in PAGE_SIZE frames.
> 
> Handle this in xennet_make_frags by iterating over the frames which
> make up the page.
> 
> This is the netfront equivalent to 6a8ed462f16b for netback.
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: netdev@vger.kernel.org
> Cc: xen-devel@lists.xen.org
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>
> Cc: ANNIE LI <annie.li@oracle.com>
> Cc: Sander Eikelenboom <linux@eikelenboom.it>
> Cc: Stefan Bader <stefan.bader@canonical.com>
> ---
>  drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>  1 files changed, 44 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..a12b99a 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
>  	/* Grant backend access to each skb fragment page. */
>  	for (i = 0; i < frags; i++) {
>  		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> +		struct page *page = skb_frag_page(frag);
> +		unsigned long size = skb_frag_size(frag);
> +		unsigned long offset = frag->page_offset;
>  
> -		tx->flags |= XEN_NETTXF_more_data;
> +		/* Data must not cross a page boundary. */
> +		BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>  
> -		id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> -		np->tx_skbs[id].skb = skb_get(skb);
> -		tx = RING_GET_REQUEST(&np->tx, prod++);
> -		tx->id = id;
> -		ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> -		BUG_ON((signed short)ref < 0);
> +		/* Skip unused frames from start of page */

'frame' in the comment means an order-0 page ?

> +		page += offset >> PAGE_SHIFT;
> +		offset &= ~PAGE_MASK;
>  
> -		mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
> -		gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> -						mfn, GNTMAP_readonly);
> +		while (size > 0) {
> +			unsigned long bytes;
>  
> -		tx->gref = np->grant_tx_ref[id] = ref;
> -		tx->offset = frag->page_offset;
> -		tx->size = skb_frag_size(frag);
> -		tx->flags = 0;
> +			BUG_ON(offset >= PAGE_SIZE);
> +
> +			bytes = PAGE_SIZE - offset;
> +			if (bytes > size)
> +				bytes = size;
> +
> +			tx->flags |= XEN_NETTXF_more_data;
> +
> +			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> +			np->tx_skbs[id].skb = skb_get(skb);

BTW this skb_get() means extra atomic operations for every 4096 bytes
unit, and an extra atomic op (and test for final 0) at TX completion.
This could be avoided, by setting np->tx_skbs[id].skb = skb only for the
very last unit.

> +			tx = RING_GET_REQUEST(&np->tx, prod++);
> +			tx->id = id;
> +			ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> +			BUG_ON((signed short)ref < 0);
> +
> +			mfn = pfn_to_mfn(page_to_pfn(page));
> +			gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> +							mfn, GNTMAP_readonly);
> +
> +			tx->gref = np->grant_tx_ref[id] = ref;
> +			tx->offset = offset;
> +			tx->size = bytes;
> +			tx->flags = 0;
> +
> +			offset += bytes;
> +			size -= bytes;
> +
> +			/* Next frame */
> +			if (offset == PAGE_SIZE && size) {
> +				BUG_ON(!PageCompound(page));
> +				page++;
> +				offset = 0;
> +			}
> +		}
>  	}
>  
>  	np->tx.req_prod_pvt = prod;

Acked-by: Eric Dumazet <edumazet@google.com>

Thanks !


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Ian Campbell - Nov. 20, 2012, 3:05 p.m.
On Tue, 2012-11-20 at 14:45 +0000, Eric Dumazet wrote:
> > +		/* Skip unused frames from start of page */
> 
> 'frame' in the comment means an order-0 page ?

Yes. Confusing in the context of a network driver I know! I couldn't
think of a better term.

> > +			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> > +			np->tx_skbs[id].skb = skb_get(skb);
> 
> BTW this skb_get() means extra atomic operations for every 4096 bytes
> unit, and an extra atomic op (and test for final 0) at TX completion.
> This could be avoided, by setting np->tx_skbs[id].skb = skb only for the
> very last unit.

Thanks. Might be tricky because guests can ack the individual requests
in any order but it's something worth having a look at.

> >  	np->tx.req_prod_pvt = prod;
> 
> Acked-by: Eric Dumazet <edumazet@google.com>
> 
> Thanks !

Thanks for the review.

Ian.

> 
> 


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annie.li@oracle.com - Nov. 21, 2012, 2:52 a.m.
On 2012-11-20 19:40, Ian Campbell wrote:
> An SKB paged fragment can consist of a compound page with order>  0.
> However the netchannel protocol deals only in PAGE_SIZE frames.
>
> Handle this in xennet_make_frags by iterating over the frames which
> make up the page.
>
> This is the netfront equivalent to 6a8ed462f16b for netback.
>
> Signed-off-by: Ian Campbell<ian.campbell@citrix.com>
> Cc: netdev@vger.kernel.org
> Cc: xen-devel@lists.xen.org
> Cc: Eric Dumazet<edumazet@google.com>
> Cc: Konrad Rzeszutek Wilk<konrad@kernel.org>
> Cc: ANNIE LI<annie.li@oracle.com>
> Cc: Sander Eikelenboom<linux@eikelenboom.it>
> Cc: Stefan Bader<stefan.bader@canonical.com>
> ---
>   drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>   1 files changed, 44 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..a12b99a 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
>   	/* Grant backend access to each skb fragment page. */
>   	for (i = 0; i<  frags; i++) {
>   		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> +		struct page *page = skb_frag_page(frag);
> +		unsigned long size = skb_frag_size(frag);
> +		unsigned long offset = frag->page_offset;

There are following definitions at the beginning of xennet_make_frags,

         unsigned int offset = offset_in_page(data);
         unsigned int len = skb_headlen(skb);

Is it better to reuse those definitions, and not define new size and 
offset again in this for loop? And unsigned int is enough here, right?

>
> -		tx->flags |= XEN_NETTXF_more_data;
> +		/* Data must not cross a page boundary. */
> +		BUG_ON(size + offset>  PAGE_SIZE<<compound_order(page));
>
> -		id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> -		np->tx_skbs[id].skb = skb_get(skb);
> -		tx = RING_GET_REQUEST(&np->tx, prod++);
> -		tx->id = id;
> -		ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> -		BUG_ON((signed short)ref<  0);
> +		/* Skip unused frames from start of page */
> +		page += offset>>  PAGE_SHIFT;
> +		offset&= ~PAGE_MASK;
>
> -		mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
> -		gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> -						mfn, GNTMAP_readonly);
> +		while (size>  0) {
> +			unsigned long bytes;
>
> -		tx->gref = np->grant_tx_ref[id] = ref;
> -		tx->offset = frag->page_offset;
> -		tx->size = skb_frag_size(frag);
> -		tx->flags = 0;
> +			BUG_ON(offset>= PAGE_SIZE);
> +
> +			bytes = PAGE_SIZE - offset;
> +			if (bytes>  size)
> +				bytes = size;
> +
> +			tx->flags |= XEN_NETTXF_more_data;
> +
> +			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
Over 80 characters?
> +			np->tx_skbs[id].skb = skb_get(skb);
> +			tx = RING_GET_REQUEST(&np->tx, prod++);
> +			tx->id = id;
> +			ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> +			BUG_ON((signed short)ref<  0);
> +
> +			mfn = pfn_to_mfn(page_to_pfn(page));
> +			gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> +							mfn, GNTMAP_readonly);
Over 80 characters?

Thanks
Annie
> +
> +			tx->gref = np->grant_tx_ref[id] = ref;
> +			tx->offset = offset;
> +			tx->size = bytes;
> +			tx->flags = 0;
> +
> +			offset += bytes;
> +			size -= bytes;
> +
> +			/* Next frame */
> +			if (offset == PAGE_SIZE&&  size) {
> +				BUG_ON(!PageCompound(page));
> +				page++;
> +				offset = 0;
> +			}
> +		}
>   	}
>
>   	np->tx.req_prod_pvt = prod;
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Ian Campbell - Nov. 21, 2012, 11:09 a.m.
On Wed, 2012-11-21 at 02:52 +0000, ANNIE LI wrote:
> 
> On 2012-11-20 19:40, Ian Campbell wrote:
> > An SKB paged fragment can consist of a compound page with order>  0.
> > However the netchannel protocol deals only in PAGE_SIZE frames.
> >
> > Handle this in xennet_make_frags by iterating over the frames which
> > make up the page.
> >
> > This is the netfront equivalent to 6a8ed462f16b for netback.
> >
> > Signed-off-by: Ian Campbell<ian.campbell@citrix.com>
> > Cc: netdev@vger.kernel.org
> > Cc: xen-devel@lists.xen.org
> > Cc: Eric Dumazet<edumazet@google.com>
> > Cc: Konrad Rzeszutek Wilk<konrad@kernel.org>
> > Cc: ANNIE LI<annie.li@oracle.com>
> > Cc: Sander Eikelenboom<linux@eikelenboom.it>
> > Cc: Stefan Bader<stefan.bader@canonical.com>
> > ---
> >   drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
> >   1 files changed, 44 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> > index caa0110..a12b99a 100644
> > --- a/drivers/net/xen-netfront.c
> > +++ b/drivers/net/xen-netfront.c
> > @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
> >   	/* Grant backend access to each skb fragment page. */
> >   	for (i = 0; i<  frags; i++) {
> >   		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> > +		struct page *page = skb_frag_page(frag);
> > +		unsigned long size = skb_frag_size(frag);
> > +		unsigned long offset = frag->page_offset;
> 
> There are following definitions at the beginning of xennet_make_frags,
> 
>          unsigned int offset = offset_in_page(data);
>          unsigned int len = skb_headlen(skb);

So they are, well spotted.

> Is it better to reuse those definitions, and not define new size and 
> offset again in this for loop? And unsigned int is enough here, right?

Yes to both.
> [...]
> Over 80 characters?
[...]
> Over 80 characters?

Both fixed, thanks for your review.

Ian.

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Patch

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index caa0110..a12b99a 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -452,24 +452,54 @@  static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
 	/* Grant backend access to each skb fragment page. */
 	for (i = 0; i < frags; i++) {
 		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
+		struct page *page = skb_frag_page(frag);
+		unsigned long size = skb_frag_size(frag);
+		unsigned long offset = frag->page_offset;
 
-		tx->flags |= XEN_NETTXF_more_data;
+		/* Data must not cross a page boundary. */
+		BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
 
-		id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
-		np->tx_skbs[id].skb = skb_get(skb);
-		tx = RING_GET_REQUEST(&np->tx, prod++);
-		tx->id = id;
-		ref = gnttab_claim_grant_reference(&np->gref_tx_head);
-		BUG_ON((signed short)ref < 0);
+		/* Skip unused frames from start of page */
+		page += offset >> PAGE_SHIFT;
+		offset &= ~PAGE_MASK;
 
-		mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
-		gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
-						mfn, GNTMAP_readonly);
+		while (size > 0) {
+			unsigned long bytes;
 
-		tx->gref = np->grant_tx_ref[id] = ref;
-		tx->offset = frag->page_offset;
-		tx->size = skb_frag_size(frag);
-		tx->flags = 0;
+			BUG_ON(offset >= PAGE_SIZE);
+
+			bytes = PAGE_SIZE - offset;
+			if (bytes > size)
+				bytes = size;
+
+			tx->flags |= XEN_NETTXF_more_data;
+
+			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
+			np->tx_skbs[id].skb = skb_get(skb);
+			tx = RING_GET_REQUEST(&np->tx, prod++);
+			tx->id = id;
+			ref = gnttab_claim_grant_reference(&np->gref_tx_head);
+			BUG_ON((signed short)ref < 0);
+
+			mfn = pfn_to_mfn(page_to_pfn(page));
+			gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
+							mfn, GNTMAP_readonly);
+
+			tx->gref = np->grant_tx_ref[id] = ref;
+			tx->offset = offset;
+			tx->size = bytes;
+			tx->flags = 0;
+
+			offset += bytes;
+			size -= bytes;
+
+			/* Next frame */
+			if (offset == PAGE_SIZE && size) {
+				BUG_ON(!PageCompound(page));
+				page++;
+				offset = 0;
+			}
+		}
 	}
 
 	np->tx.req_prod_pvt = prod;