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Message-ID: <20190321033941.bygpejl2krltkdmm@ast-mbp.dhcp.thefacebook.com>
Date: Wed, 20 Mar 2019 20:39:42 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Stanislav Fomichev <sdf@...gle.com>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
ast@...nel.org, daniel@...earbox.net, simon.horman@...ronome.com,
willemb@...gle.com, peterpenkov96@...il.com
Subject: Re: [RFC bpf-next v2 1/9] net: introduce __init_skb{,_data,_shinfo}
helpers
On Tue, Mar 19, 2019 at 03:19:40PM -0700, Stanislav Fomichev wrote:
> __init_skb is essentially a version of __build_skb which accepts skb as
> an argument (instead of doing kmem_cache_alloc to allocate it).
>
> __init_skb_shinfo initializes shinfo.
>
> __init_skb_data initializes skb data pointers.
>
> No functional changes.
>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
> include/linux/skbuff.h | 14 ++++++++++
> net/core/skbuff.c | 60 +++++++++++++++++-------------------------
> 2 files changed, 38 insertions(+), 36 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 9027a8c4219f..e8c1d5b97f96 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -4399,5 +4399,19 @@ static inline __wsum lco_csum(struct sk_buff *skb)
> return csum_partial(l4_hdr, csum_start - l4_hdr, partial);
> }
>
> +static inline void __init_skb_data(struct sk_buff *skb, u8 *data,
> + unsigned int size)
> +{
> + /* Account for allocated memory : skb + skb->head */
> + skb->truesize = SKB_TRUESIZE(size);
> + refcount_set(&skb->users, 1);
> + skb->head = data;
> + skb->data = data;
> + skb_reset_tail_pointer(skb);
> + skb->end = skb->tail + size;
> + skb->mac_header = (typeof(skb->mac_header))~0U;
> + skb->transport_header = (typeof(skb->transport_header))~0U;
> +}
> +
> #endif /* __KERNEL__ */
> #endif /* _LINUX_SKBUFF_H */
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 2415d9cb9b89..b413354ee709 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -160,6 +160,26 @@ static void *__kmalloc_reserve(size_t size, gfp_t flags, int node,
> *
> */
>
> +static inline void __init_skb(struct sk_buff *skb, u8 *data, unsigned int size)
> +{
> + /* Only clear those fields we need to clear, not those that we will
> + * actually initialize below. Hence, don't put any more fields after
> + * the tail pointer in struct sk_buff!
> + */
> + memset(skb, 0, offsetof(struct sk_buff, tail));
> + __init_skb_data(skb, data, size);
> +}
> +
> +static inline void __init_skb_shinfo(struct sk_buff *skb)
> +{
> + struct skb_shared_info *shinfo;
> +
> + /* make sure we initialize shinfo sequentially */
> + shinfo = skb_shinfo(skb);
> + memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
> + atomic_set(&shinfo->dataref, 1);
> +}
> +
> /**
> * __alloc_skb - allocate a network buffer
> * @size: size to allocate
> @@ -181,7 +201,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
> int flags, int node)
> {
> struct kmem_cache *cache;
> - struct skb_shared_info *shinfo;
> struct sk_buff *skb;
> u8 *data;
> bool pfmemalloc;
> @@ -215,27 +234,9 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
> size = SKB_WITH_OVERHEAD(ksize(data));
> prefetchw(data + size);
>
> - /*
> - * Only clear those fields we need to clear, not those that we will
> - * actually initialise below. Hence, don't put any more fields after
> - * the tail pointer in struct sk_buff!
> - */
> - memset(skb, 0, offsetof(struct sk_buff, tail));
> - /* Account for allocated memory : skb + skb->head */
> - skb->truesize = SKB_TRUESIZE(size);
> + __init_skb(skb, data, size);
> + __init_skb_shinfo(skb);
> skb->pfmemalloc = pfmemalloc;
> - refcount_set(&skb->users, 1);
> - skb->head = data;
> - skb->data = data;
> - skb_reset_tail_pointer(skb);
> - skb->end = skb->tail + size;
> - skb->mac_header = (typeof(skb->mac_header))~0U;
> - skb->transport_header = (typeof(skb->transport_header))~0U;
> -
> - /* make sure we initialize shinfo sequentially */
> - shinfo = skb_shinfo(skb);
> - memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
> - atomic_set(&shinfo->dataref, 1);
>
> if (flags & SKB_ALLOC_FCLONE) {
> struct sk_buff_fclones *fclones;
> @@ -277,7 +278,6 @@ EXPORT_SYMBOL(__alloc_skb);
> */
> struct sk_buff *__build_skb(void *data, unsigned int frag_size)
> {
> - struct skb_shared_info *shinfo;
> struct sk_buff *skb;
> unsigned int size = frag_size ? : ksize(data);
>
> @@ -287,20 +287,8 @@ struct sk_buff *__build_skb(void *data, unsigned int frag_size)
>
> size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
> - memset(skb, 0, offsetof(struct sk_buff, tail));
> - skb->truesize = SKB_TRUESIZE(size);
> - refcount_set(&skb->users, 1);
> - skb->head = data;
> - skb->data = data;
> - skb_reset_tail_pointer(skb);
> - skb->end = skb->tail + size;
> - skb->mac_header = (typeof(skb->mac_header))~0U;
> - skb->transport_header = (typeof(skb->transport_header))~0U;
> -
> - /* make sure we initialize shinfo sequentially */
> - shinfo = skb_shinfo(skb);
> - memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
> - atomic_set(&shinfo->dataref, 1);
> + __init_skb(skb, data, size);
> + __init_skb_shinfo(skb);
I think you need to convince Dave and Eric that
above surgery is necessary to do the hack in patch 6 with
+static DEFINE_PER_CPU(struct sk_buff, bpf_flow_skb);
I think the better option it to introduce new prog type that works
without skb. I think it can be pretty close to shape and form to xdp.
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