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Date: Thu, 26 May 2011 13:24:02 -0700
From: Shirley Ma <mashirle@...ibm.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: David Miller <davem@...emloft.net>, mst@...hat.com,
Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
netdev@...r.kernel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 2/4 net-next] skbuff: Add userspace zero-copy
buffers in skb
On Thu, 2011-05-26 at 22:04 +0200, Eric Dumazet wrote:
> Le jeudi 26 mai 2011 à 12:36 -0700, Shirley Ma a écrit :
> > 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 to hold these userspace buffers too long.
> >
> > Signed-off-by: Shirley Ma <xma@...ibm.com>
> > ---
> >
> > include/linux/skbuff.h | 26 +++++++++++++++
> > net/core/skbuff.c | 80
> ++++++++++++++++++++++++++++++++++++++++++++++-
> > 2 files changed, 104 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index d0ae90a..025de5c 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -189,6 +189,18 @@ enum {
> > SKBTX_DRV_NEEDS_SK_REF = 1 << 3,
> > };
> >
> > +/*
> > + * 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 skb_ubuf_info {
> > + /* support buffers allocation from userspace */
> > + void (*callback)(struct sk_buff *);
> > + void *arg;
> > + size_t desc;
> > +};
>
> Thats 24 bytes on each skb... desc for example is not used in this
> patch (yes, its used later in patch 4/4)
>
> But still... could you instead use one pointer only in skb ?
I could reduce callback pointer by moving it to *arg, but not desc, this
indicates that which buffer DMA hasn't done yet in *arg.
>
> > +
> > /* This data is invariant across clones and lives at
> > * the end of the header data, ie. at skb->end.
> > */
> > @@ -211,6 +223,10 @@ struct skb_shared_info {
> > /* Intermediate layers must ensure that destructor_arg
> > * remains valid until skb destructor */
> > void * destructor_arg;
> > +
> > + /* DMA mapping from/to userspace buffers */
> > + struct skb_ubuf_info ubuf;
> > +
> > /* must be last field, see pskb_expand_head() */
> > skb_frag_t frags[MAX_SKB_FRAGS];
> > };
> > @@ -2261,5 +2277,15 @@ static inline void
> skb_checksum_none_assert(struct sk_buff *skb)
> > }
> >
> > bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
> > +
> > +/*
> > + * skb_ubuf - is the buffer from userspace
> > + * @skb: buffer to check
> > + */
> > +static inline int skb_ubuf(const struct sk_buff *skb)
> > +{
> > + return (skb_shinfo(skb)->ubuf.callback != NULL);
>
> return skb_shinfo(skb)->ubuf.callback != NULL;
>
> > +}
> > +
> > #endif /* __KERNEL__ */
> > #endif /* _LINUX_SKBUFF_H */
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 7ebeed0..890447c 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -210,6 +210,8 @@ struct sk_buff *__alloc_skb(unsigned int size,
> gfp_t gfp_mask,
> > shinfo = skb_shinfo(skb);
> > memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
> > atomic_set(&shinfo->dataref, 1);
> > + shinfo->ubuf.callback = NULL;
> > + shinfo->ubuf.arg = NULL;
>
> if you put ubuf ptr before dataref, no need to add this (the memset()
> clear all shared_info up to dataref)
Ok, will remove it.
> > kmemcheck_annotate_variable(shinfo->destructor_arg);
> >
> > if (fclone) {
> > @@ -328,6 +330,14 @@ 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_ubuf(skb)) {
> > + skb_shinfo(skb)->ubuf.callback(skb);
> > + skb_shinfo(skb)->ubuf.callback = NULL;
> > + }
> > if (skb_has_frag_list(skb))
> > skb_drop_fraglist(skb);
> >
> > @@ -480,6 +490,9 @@ bool skb_recycle_check(struct sk_buff *skb, int
> skb_size)
> > if (irqs_disabled())
> > return false;
> >
> > + if (skb_ubuf(skb))
> > + return false;
> > +
> > if (skb_is_nonlinear(skb) || skb->fclone !=
> SKB_FCLONE_UNAVAILABLE)
> > return false;
> >
> > @@ -572,6 +585,7 @@ static struct sk_buff *__skb_clone(struct
> sk_buff *n, struct sk_buff *skb)
> > atomic_set(&n->users, 1);
> >
> > atomic_inc(&(skb_shinfo(skb)->dataref));
> > + skb_shinfo(skb)->ubuf.callback = NULL;
> > skb->cloned = 1;
> >
> > return n;
> > @@ -595,6 +609,48 @@ 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;
> > +
> > + 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);
> > + skb_shinfo(skb)->ubuf.callback(skb);
> > + skb_shinfo(skb)->ubuf.callback = NULL;
> > +
> > + /* 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
> > @@ -613,6 +669,11 @@ struct sk_buff *skb_clone(struct sk_buff *skb,
> gfp_t gfp_mask)
> > {
> > struct sk_buff *n;
> >
> > + if (skb_ubuf(skb)) {
> > + if (skb_copy_ubufs(skb, gfp_mask))
> > + return NULL;
> > + }
> > +
> > n = skb + 1;
> > if (skb->fclone == SKB_FCLONE_ORIG &&
> > n->fclone == SKB_FCLONE_UNAVAILABLE) {
> > @@ -730,6 +791,12 @@ struct sk_buff *pskb_copy(struct sk_buff *skb,
> gfp_t gfp_mask)
> > if (skb_shinfo(skb)->nr_frags) {
> > int i;
> >
> > + if (skb_ubuf(skb)) {
> > + 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);
> > @@ -743,6 +810,7 @@ struct sk_buff *pskb_copy(struct sk_buff *skb,
> gfp_t gfp_mask)
> > }
> >
> > copy_skb_header(n, skb);
> > +
>
> please dont add new lines like this in your patch
checkpatch doesn't check this kind of line, will remove it.
> > out:
> > return n;
> > }
> > @@ -787,7 +855,6 @@ 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;
> > -
>
> and dont delete this one as well.
>
> > fastpath = atomic_read(&skb_shinfo(skb)->dataref) ==
> delta;
> > }
> >
> > @@ -818,14 +885,19 @@ 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_ubuf(skb)) {
> > + 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);
> > -
>
> ditto
>
> > if (skb_has_frag_list(skb))
> > skb_clone_fraglist(skb);
> >
> > skb_release_data(skb);
> > }
> > +
>
> ditto
>
> > off = (data + nhead) - skb->head;
> >
> > skb->head = data;
> > @@ -852,6 +924,8 @@ adjust_others:
> > atomic_set(&skb_shinfo(skb)->dataref, 1);
> > return 0;
> >
> > +nofrags:
> > + kfree(data);
> > nodata:
> > return -ENOMEM;
> > }
> > @@ -1353,6 +1427,8 @@ int skb_copy_bits(const struct sk_buff *skb,
> int offset, void *to, int len)
> > }
> > start = end;
> > }
> > + skb_shinfo(skb)->ubuf.callback = NULL;
> > +
> > if (!len)
> > return 0;
> >
> >
> >
>
>
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