net/core/skbuff.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *	Routines having to do with the 'struct sk_buff' memory handlers.
 *
 *	Authors:	Alan Cox <alan@lxorguk.ukuu.org.uk>
 *			Florian La Roche <rzsfl@rz.uni-sb.de>
 *
 *	Fixes:
 *		Alan Cox	:	Fixed the worst of the load
 *					balancer bugs.
 *		Dave Platt	:	Interrupt stacking fix.
 *	Richard Kooijman	:	Timestamp fixes.
 *		Alan Cox	:	Changed buffer format.
 *		Alan Cox	:	destructor hook for AF_UNIX etc.
 *		Linus Torvalds	:	Better skb_clone.
 *		Alan Cox	:	Added skb_copy.
 *		Alan Cox	:	Added all the changed routines Linus
 *					only put in the headers
 *		Ray VanTassle	:	Fixed --skb->lock in free
 *		Alan Cox	:	skb_copy copy arp field
 *		Andi Kleen	:	slabified it.
 *		Robert Olsson	:	Removed skb_head_pool
 *
 *	NOTE:
 *		The __skb_ routines should be called with interrupts
 *	disabled, or you better be *real* sure that the operation is atomic
 *	with respect to whatever list is being frobbed (e.g. via lock_sock()
 *	or via disabling bottom half handlers, etc).
 */

/*
 *	The functions in this file will not compile correctly with gcc 2.4.x
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/slab.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/sctp.h>
#include <linux/netdevice.h>
#ifdef CONFIG_NET_CLS_ACT
#include <net/pkt_sched.h>
#endif
#include <linux/string.h>
#include <linux/skbuff.h>
#include <linux/skbuff_ref.h>
#include <linux/splice.h>
#include <linux/cache.h>
#include <linux/rtnetlink.h>
#include <linux/init.h>
#include <linux/scatterlist.h>
#include <linux/errqueue.h>
#include <linux/prefetch.h>
#include <linux/bitfield.h>
#include <linux/if_vlan.h>
#include <linux/mpls.h>
#include <linux/kcov.h>
#include <linux/iov_iter.h>

#include <net/protocol.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <net/gso.h>
#include <net/hotdata.h>
#include <net/ip6_checksum.h>
#include <net/xfrm.h>
#include <net/mpls.h>
#include <net/mptcp.h>
#include <net/mctp.h>
#include <net/page_pool/helpers.h>
#include <net/dropreason.h>

#include <linux/uaccess.h>
#include <trace/events/skb.h>
#include <linux/highmem.h>
#include <linux/capability.h>
#include <linux/user_namespace.h>
#include <linux/indirect_call_wrapper.h>
#include <linux/textsearch.h>

#include "dev.h"
#include "sock_destructor.h"

#ifdef CONFIG_SKB_EXTENSIONS
static struct kmem_cache *skbuff_ext_cache __ro_after_init;
#endif

#define SKB_SMALL_HEAD_SIZE SKB_HEAD_ALIGN(MAX_TCP_HEADER)

/* We want SKB_SMALL_HEAD_CACHE_SIZE to not be a power of two.
 * This should ensure that SKB_SMALL_HEAD_HEADROOM is a unique
 * size, and we can differentiate heads from skb_small_head_cache
 * vs system slabs by looking at their size (skb_end_offset()).
 */
#define SKB_SMALL_HEAD_CACHE_SIZE					\
	(is_power_of_2(SKB_SMALL_HEAD_SIZE) ?			\
		(SKB_SMALL_HEAD_SIZE + L1_CACHE_BYTES) :	\
		SKB_SMALL_HEAD_SIZE)

#define SKB_SMALL_HEAD_HEADROOM						\
	SKB_WITH_OVERHEAD(SKB_SMALL_HEAD_CACHE_SIZE)

/* kcm_write_msgs() relies on casting paged frags to bio_vec to use
 * iov_iter_bvec(). These static asserts ensure the cast is valid is long as the
 * netmem is a page.
 */
static_assert(offsetof(struct bio_vec, bv_page) ==
	      offsetof(skb_frag_t, netmem));
static_assert(sizeof_field(struct bio_vec, bv_page) ==
	      sizeof_field(skb_frag_t, netmem));

static_assert(offsetof(struct bio_vec, bv_len) == offsetof(skb_frag_t, len));
static_assert(sizeof_field(struct bio_vec, bv_len) ==
	      sizeof_field(skb_frag_t, len));

static_assert(offsetof(struct bio_vec, bv_offset) ==
	      offsetof(skb_frag_t, offset));
static_assert(sizeof_field(struct bio_vec, bv_offset) ==
	      sizeof_field(skb_frag_t, offset));

#undef FN
#define FN(reason) [SKB_DROP_REASON_##reason] = #reason,
static const char * const drop_reasons[] = {
	[SKB_CONSUMED] = "CONSUMED",
	DEFINE_DROP_REASON(FN, FN)
};

static const struct drop_reason_list drop_reasons_core = {
	.reasons = drop_reasons,
	.n_reasons = ARRAY_SIZE(drop_reasons),
};

const struct drop_reason_list __rcu *
drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
	[SKB_DROP_REASON_SUBSYS_CORE] = RCU_INITIALIZER(&drop_reasons_core),
};
EXPORT_SYMBOL(drop_reasons_by_subsys);

/**
 * drop_reasons_register_subsys - register another drop reason subsystem
 * @subsys: the subsystem to register, must not be the core
 * @list: the list of drop reasons within the subsystem, must point to
 *	a statically initialized list
 */
void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
				  const struct drop_reason_list *list)
{
	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
		 "invalid subsystem %d\n", subsys))
		return;

	/* must point to statically allocated memory, so INIT is OK */
	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], list);
}
EXPORT_SYMBOL_GPL(drop_reasons_register_subsys);

/**
 * drop_reasons_unregister_subsys - unregister a drop reason subsystem
 * @subsys: the subsystem to remove, must not be the core
 *
 * Note: This will synchronize_rcu() to ensure no users when it returns.
 */
void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys)
{
	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
		 "invalid subsystem %d\n", subsys))
		return;

	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], NULL);

	synchronize_rcu();
}
EXPORT_SYMBOL_GPL(drop_reasons_unregister_subsys);

/**
 *	skb_panic - private function for out-of-line support
 *	@skb:	buffer
 *	@sz:	size
 *	@addr:	address
 *	@msg:	skb_over_panic or skb_under_panic
 *
 *	Out-of-line support for skb_put() and skb_push().
 *	Called via the wrapper skb_over_panic() or skb_under_panic().
 *	Keep out of line to prevent kernel bloat.
 *	__builtin_return_address is not used because it is not always reliable.
 */
static void skb_panic(struct sk_buff *skb, unsigned int sz, void *addr,
		      const char msg[])
{
	pr_emerg("%s: text:%px len:%d put:%d head:%px data:%px tail:%#lx end:%#lx dev:%s\n",
		 msg, addr, skb->len, sz, skb->head, skb->data,
		 (unsigned long)skb->tail, (unsigned long)skb->end,
		 skb->dev ? skb->dev->name : "<NULL>");
	BUG();
}

static void skb_over_panic(struct sk_buff *skb, unsigned int sz, void *addr)
{
	skb_panic(skb, sz, addr, __func__);
}

static void skb_under_panic(struct sk_buff *skb, unsigned int sz, void *addr)
{
	skb_panic(skb, sz, addr, __func__);
}

#define NAPI_SKB_CACHE_SIZE	64
#define NAPI_SKB_CACHE_BULK	16
#define NAPI_SKB_CACHE_HALF	(NAPI_SKB_CACHE_SIZE / 2)

#if PAGE_SIZE == SZ_4K

#define NAPI_HAS_SMALL_PAGE_FRAG	1
#define NAPI_SMALL_PAGE_PFMEMALLOC(nc)	((nc).pfmemalloc)

/* specialized page frag allocator using a single order 0 page
 * and slicing it into 1K sized fragment. Constrained to systems
 * with a very limited amount of 1K fragments fitting a single
 * page - to avoid excessive truesize underestimation
 */

struct page_frag_1k {
	void *va;
	u16 offset;
	bool pfmemalloc;
};

static void *page_frag_alloc_1k(struct page_frag_1k *nc, gfp_t gfp)
{
	struct page *page;
	int offset;

	offset = nc->offset - SZ_1K;
	if (likely(offset >= 0))
		goto use_frag;

	page = alloc_pages_node(NUMA_NO_NODE, gfp, 0);
	if (!page)
		return NULL;

	nc->va = page_address(page);
	nc->pfmemalloc = page_is_pfmemalloc(page);
	offset = PAGE_SIZE - SZ_1K;
	page_ref_add(page, offset / SZ_1K);

use_frag:
	nc->offset = offset;
	return nc->va + offset;
}
#else

/* the small page is actually unused in this build; add dummy helpers
 * to please the compiler and avoid later preprocessor's conditionals
 */
#define NAPI_HAS_SMALL_PAGE_FRAG	0
#define NAPI_SMALL_PAGE_PFMEMALLOC(nc)	false

struct page_frag_1k {
};

static void *page_frag_alloc_1k(struct page_frag_1k *nc, gfp_t gfp_mask)
{
	return NULL;
}

#endif

struct napi_alloc_cache {
	local_lock_t bh_lock;
	struct page_frag_cache page;
	struct page_frag_1k page_small;
	unsigned int skb_count;
	void *skb_cache[NAPI_SKB_CACHE_SIZE];
};

static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);
static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache) = {
	.bh_lock = INIT_LOCAL_LOCK(bh_lock),
};

/* Double check that napi_get_frags() allocates skbs with
 * skb->head being backed by slab, not a page fragment.
 * This is to make sure bug fixed in 3226b158e67c
 * ("net: avoid 32 x truesize under-estimation for tiny skbs")
 * does not accidentally come back.
 */
void napi_get_frags_check(struct napi_struct *napi)
{
	struct sk_buff *skb;

	local_bh_disable();
	skb = napi_get_frags(napi);
	WARN_ON_ONCE(!NAPI_HAS_SMALL_PAGE_FRAG && skb && skb->head_frag);
	napi_free_frags(napi);
	local_bh_enable();
}

void *__napi_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
{
	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
	void *data;

	fragsz = SKB_DATA_ALIGN(fragsz);

	local_lock_nested_bh(&napi_alloc_cache.bh_lock);
	data = __page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC,
				       align_mask);
	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
	return data;

}
EXPORT_SYMBOL(__napi_alloc_frag_align);

void *__netdev_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
{
	void *data;

	if (in_hardirq() || irqs_disabled()) {
		struct page_frag_cache *nc = this_cpu_ptr(&netdev_alloc_cache);

		fragsz = SKB_DATA_ALIGN(fragsz);
		data = __page_frag_alloc_align(nc, fragsz, GFP_ATOMIC,
					       align_mask);
	} else {
		local_bh_disable();
		data = __napi_alloc_frag_align(fragsz, align_mask);
		local_bh_enable();
	}
	return data;
}
EXPORT_SYMBOL(__netdev_alloc_frag_align);

static struct sk_buff *napi_skb_cache_get(void)
{
	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
	struct sk_buff *skb;

	local_lock_nested_bh(&napi_alloc_cache.bh_lock);
	if (unlikely(!nc->skb_count)) {
		nc->skb_count = kmem_cache_alloc_bulk(net_hotdata.skbuff_cache,
						      GFP_ATOMIC,
						      NAPI_SKB_CACHE_BULK,
						      nc->skb_cache);
		if (unlikely(!nc->skb_count)) {
			local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
			return NULL;
		}
	}

	skb = nc->skb_cache[--nc->skb_count];
	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
	kasan_mempool_unpoison_object(skb, kmem_cache_size(net_hotdata.skbuff_cache));

	return skb;
}

static inline void __finalize_skb_around(struct sk_buff *skb, void *data,
					 unsigned int size)
{
	struct skb_shared_info *shinfo;

	size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

	/* Assumes caller memset cleared SKB */
	skb->truesize = SKB_TRUESIZE(size);
	refcount_set(&skb->users, 1);
	skb->head = data;
	skb->data = data;
	skb_reset_tail_pointer(skb);
	skb_set_end_offset(skb, size);
	skb->mac_header = (typeof(skb->mac_header))~0U;
	skb->transport_header = (typeof(skb->transport_header))~0U;
	skb->alloc_cpu = raw_smp_processor_id();
	/* make sure we initialize shinfo sequentially */
	shinfo = skb_shinfo(skb);
	memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
	atomic_set(&shinfo->dataref, 1);

	skb_set_kcov_handle(skb, kcov_common_handle());
}

static inline void *__slab_build_skb(struct sk_buff *skb, void *data,
				     unsigned int *size)
{
	void *resized;

	/* Must find the allocation size (and grow it to match). */
	*size = ksize(data);
	/* krealloc() will immediately return "data" when
	 * "ksize(data)" is requested: it is the existing upper
	 * bounds. As a result, GFP_ATOMIC will be ignored. Note
	 * that this "new" pointer needs to be passed back to the
	 * caller for use so the __alloc_size hinting will be
	 * tracked correctly.
	 */
	resized = krealloc(data, *size, GFP_ATOMIC);
	WARN_ON_ONCE(resized != data);
	return resized;
}

/* build_skb() variant which can operate on slab buffers.
 * Note that this should be used sparingly as slab buffers
 * cannot be combined efficiently by GRO!
 */
struct sk_buff *slab_build_skb(void *data)
{
	struct sk_buff *skb;
	unsigned int size;

	skb = kmem_cache_alloc(net_hotdata.skbuff_cache, GFP_ATOMIC);
	if (unlikely(!skb))
		return NULL;

	memset(skb, 0, offsetof(struct sk_buff, tail));
	data = __slab_build_skb(skb, data, &size);
	__finalize_skb_around(skb, data, size);

	return skb;
}
EXPORT_SYMBOL(slab_build_skb);

/* Caller must provide SKB that is memset cleared */
static void __build_skb_around(struct sk_buff *skb, void *data,
			       unsigned int frag_size)
{
	unsigned int size = frag_size;

	/* frag_size == 0 is considered deprecated now. Callers
	 * using slab buffer should use slab_build_skb() instead.
	 */
	if (WARN_ONCE(size == 0, "Use slab_build_skb() instead"))
		data = __slab_build_skb(skb, data, &size);

	__finalize_skb_around(skb, data, size);
}

/**
 * __build_skb - build a network buffer
 * @data: data buffer provided by caller
 * @frag_size: size of data (must not be 0)
 *
 * Allocate a new &sk_buff. Caller provides space holding head and
 * skb_shared_info. @data must have been allocated from the page
 * allocator or vmalloc(). (A @frag_size of 0 to indicate a kmalloc()
 * allocation is deprecated, and callers should use slab_build_skb()
 * instead.)
 * The return is the new skb buffer.
 * On a failure the return is %NULL, and @data is not freed.
 * Notes :
 *  Before IO, driver allocates only data buffer where NIC put incoming frame
 *  Driver should add room at head (NET_SKB_PAD) and
 *  MUST add room at tail (SKB_DATA_ALIGN(skb_shared_info))
 *  After IO, driver calls build_skb(), to allocate sk_buff and populate it
 *  before giving packet to stack.
 *  RX rings only contains data buffers, not full skbs.
 */
struct sk_buff *__build_skb(void *data, unsigned int frag_size)
{
	struct sk_buff *skb;

	skb = kmem_cache_alloc(net_hotdata.skbuff_cache, GFP_ATOMIC);
	if (unlikely(!skb))
		return NULL;

	memset(skb, 0, offsetof(struct sk_buff, tail));
	__build_skb_around(skb, data, frag_size);

	return skb;
}

/* build_skb() is wrapper over __build_skb(), that specifically
 * takes care of skb->head and skb->pfmemalloc
 */
struct sk_buff *build_skb(void *data, unsigned int frag_size)
{
	struct sk_buff *skb = __build_skb(data, frag_size);

	if (likely(skb && frag_size)) {
		skb->head_frag = 1;
		skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
	}
	return skb;
}
EXPORT_SYMBOL(build_skb);

/**
 * build_skb_around - build a network buffer around provided skb
 * @skb: sk_buff provide by caller, must be memset cleared
 * @data: data buffer provided by caller
 * @frag_size: size of data
 */
struct sk_buff *build_skb_around(struct sk_buff *skb,
				 void *data, unsigned int frag_size)
{
	if (unlikely(!skb))
		return NULL;

	__build_skb_around(skb, data, frag_size);

	if (frag_size) {
		skb->head_frag = 1;
		skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
	}
	return skb;
}
EXPORT_SYMBOL(build_skb_around);

/**
 * __napi_build_skb - build a network buffer
 * @data: data buffer provided by caller
 * @frag_size: size of data
 *
 * Version of __build_skb() that uses NAPI percpu caches to obtain
 * skbuff_head instead of inplace allocation.
 *
 * Returns a new &sk_buff on success, %NULL on allocation failure.
 */
static struct sk_buff *__napi_build_skb(void *data, unsigned int frag_size)
{
	struct sk_buff *skb;

	skb = napi_skb_cache_get();
	if (unlikely(!skb))
		return NULL;

	memset(skb, 0, offsetof(struct sk_buff, tail));
	__build_skb_around(skb, data, frag_size);

	return skb;
}

/**
 * napi_build_skb - build a network buffer
 * @data: data buffer provided by caller
 * @frag_size: size of data
 *
 * Version of __napi_build_skb() that takes care of skb->head_frag
 * and skb->pfmemalloc when the data is a page or page fragment.
 *
 * Returns a new &sk_buff on success, %NULL on allocation failure.
 */
struct sk_buff *napi_build_skb(void *data, unsigned int frag_size)
{
	struct sk_buff *skb = __napi_build_skb(data, frag_size);

	if (likely(skb) && frag_size) {
		skb->head_frag = 1;
		skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
	}

	return skb;
}
EXPORT_SYMBOL(napi_build_skb);

/*
 * kmalloc_reserve is a wrapper around kmalloc_node_track_caller that tells
 * the caller if emergency pfmemalloc reserves are being used. If it is and
 * the socket is later found to be SOCK_MEMALLOC then PFMEMALLOC reserves
 * may be used. Otherwise, the packet data may be discarded until enough
 * memory is free
 */
static void *kmalloc_reserve(unsigned int *size, gfp_t flags, int node,
			     bool *pfmemalloc)
{
	bool ret_pfmemalloc = false;
	size_t obj_size;
	void *obj;

	obj_size = SKB_HEAD_ALIGN(*size);
	if (obj_size <= SKB_SMALL_HEAD_CACHE_SIZE &&
	    !(flags & KMALLOC_NOT_NORMAL_BITS)) {
		obj = kmem_cache_alloc_node(net_hotdata.skb_small_head_cache,
				flags | __GFP_NOMEMALLOC | __GFP_NOWARN,
				node);
		*size = SKB_SMALL_HEAD_CACHE_SIZE;
		if (obj || !(gfp_pfmemalloc_allowed(flags)))
			goto out;
		/* Try again but now we are using pfmemalloc reserves */
		ret_pfmemalloc = true;
		obj = kmem_cache_alloc_node(net_hotdata.skb_small_head_cache, flags, node);
		goto out;
	}

	obj_size = kmalloc_size_roundup(obj_size);
	/* The following cast might truncate high-order bits of obj_size, this
	 * is harmless because kmalloc(obj_size >= 2^32) will fail anyway.
	 */
	*size = (unsigned int)obj_size;

	/*
	 * Try a regular allocation, when that fails and we're not entitled
	 * to the reserves, fail.
	 */
	obj = kmalloc_node_track_caller(obj_size,
					flags | __GFP_NOMEMALLOC | __GFP_NOWARN,
					node);
	if (obj || !(gfp_pfmemalloc_allowed(flags)))
		goto out;

	/* Try again but now we are using pfmemalloc reserves */
	ret_pfmemalloc = true;
	obj = kmalloc_node_track_caller(obj_size, flags, node);

out:
	if (pfmemalloc)
		*pfmemalloc = ret_pfmemalloc;

	return obj;
}

/* 	Allocate a new skbuff. We do this ourselves so we can fill in a few
 *	'private' fields and also do memory statistics to find all the
 *	[BEEP] leaks.
 *
 */

/**
 *	__alloc_skb	-	allocate a network buffer
 *	@size: size to allocate
 *	@gfp_mask: allocation mask
 *	@flags: If SKB_ALLOC_FCLONE is set, allocate from fclone cache
 *		instead of head cache and allocate a cloned (child) skb.
 *		If SKB_ALLOC_RX is set, __GFP_MEMALLOC will be used for
 *		allocations in case the data is required for writeback
 *	@node: numa node to allocate memory on
 *
 *	Allocate a new &sk_buff. The returned buffer has no headroom and a
 *	tail room of at least size bytes. The object has a reference count
 *	of one. The return is the buffer. On a failure the return is %NULL.
 *
 *	Buffers may only be allocated from interrupts using a @gfp_mask of
 *	%GFP_ATOMIC.
 */
struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
			    int flags, int node)
{
	struct kmem_cache *cache;
	struct sk_buff *skb;
	bool pfmemalloc;
	u8 *data;

	cache = (flags & SKB_ALLOC_FCLONE)
		? net_hotdata.skbuff_fclone_cache : net_hotdata.skbuff_cache;

	if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
		gfp_mask |= __GFP_MEMALLOC;

	/* Get the HEAD */
	if ((flags & (SKB_ALLOC_FCLONE | SKB_ALLOC_NAPI)) == SKB_ALLOC_NAPI &&
	    likely(node == NUMA_NO_NODE || node == numa_mem_id()))
		skb = napi_skb_cache_get();
	else
		skb = kmem_cache_alloc_node(cache, gfp_mask & ~GFP_DMA, node);
	if (unlikely(!skb))
		return NULL;
	prefetchw(skb);

	/* We do our best to align skb_shared_info on a separate cache
	 * line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
	 * aligned memory blocks, unless SLUB/SLAB debug is enabled.
	 * Both skb->head and skb_shared_info are cache line aligned.
	 */
	data = kmalloc_reserve(&size, gfp_mask, node, &pfmemalloc);
	if (unlikely(!data))
		goto nodata;
	/* kmalloc_size_roundup() might give us more room than requested.
	 * Put skb_shared_info exactly at the end of allocated zone,
	 * to allow max possible filling before reallocation.
	 */
	prefetchw(data + SKB_WITH_OVERHEAD(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));
	__build_skb_around(skb, data, size);
	skb->pfmemalloc = pfmemalloc;

	if (flags & SKB_ALLOC_FCLONE) {
		struct sk_buff_fclones *fclones;

		fclones = container_of(skb, struct sk_buff_fclones, skb1);

		skb->fclone = SKB_FCLONE_ORIG;
		refcount_set(&fclones->fclone_ref, 1);
	}

	return skb;

nodata:
	kmem_cache_free(cache, skb);
	return NULL;
}
EXPORT_SYMBOL(__alloc_skb);

/**
 *	__netdev_alloc_skb - allocate an skbuff for rx on a specific device
 *	@dev: network device to receive on
 *	@len: length to allocate
 *	@gfp_mask: get_free_pages mask, passed to alloc_skb
 *
 *	Allocate a new &sk_buff and assign it a usage count of one. The
 *	buffer has NET_SKB_PAD headroom built in. Users should allocate
 *	the headroom they think they need without accounting for the
 *	built in space. The built in space is used for optimisations.
 *
 *	%NULL is returned if there is no free memory.
 */
struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
				   gfp_t gfp_mask)
{
	struct page_frag_cache *nc;
	struct sk_buff *skb;
	bool pfmemalloc;
	void *data;

	len += NET_SKB_PAD;

	/* If requested length is either too small or too big,
	 * we use kmalloc() for skb->head allocation.
	 */
	if (len <= SKB_WITH_OVERHEAD(1024) ||
	    len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
	    (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
		skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
		if (!skb)
			goto skb_fail;
		goto skb_success;
	}

	len = SKB_HEAD_ALIGN(len);

	if (sk_memalloc_socks())
		gfp_mask |= __GFP_MEMALLOC;

	if (in_hardirq() || irqs_disabled()) {
		nc = this_cpu_ptr(&netdev_alloc_cache);
		data = page_frag_alloc(nc, len, gfp_mask);
		pfmemalloc = nc->pfmemalloc;
	} else {
		local_bh_disable();
		local_lock_nested_bh(&napi_alloc_cache.bh_lock);

		nc = this_cpu_ptr(&napi_alloc_cache.page);
		data = page_frag_alloc(nc, len, gfp_mask);
		pfmemalloc = nc->pfmemalloc;

		local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
		local_bh_enable();
	}

	if (unlikely(!data))
		return NULL;

	skb = __build_skb(data, len);
	if (unlikely(!skb)) {
		skb_free_frag(data);
		return NULL;
	}

	if (pfmemalloc)
		skb->pfmemalloc = 1;
	skb->head_frag = 1;

skb_success:
	skb_reserve(skb, NET_SKB_PAD);
	skb->dev = dev;

skb_fail:
	return skb;
}
EXPORT_SYMBOL(__netdev_alloc_skb);

/**
 *	napi_alloc_skb - allocate skbuff for rx in a specific NAPI instance
 *	@napi: napi instance this buffer was allocated for
 *	@len: length to allocate
 *
 *	Allocate a new sk_buff for use in NAPI receive.  This buffer will
 *	attempt to allocate the head from a special reserved region used
 *	only for NAPI Rx allocation.  By doing this we can save several
 *	CPU cycles by avoiding having to disable and re-enable IRQs.
 *
 *	%NULL is returned if there is no free memory.
 */
struct sk_buff *napi_alloc_skb(struct napi_struct *napi, unsigned int len)
{
	gfp_t gfp_mask = GFP_ATOMIC | __GFP_NOWARN;
	struct napi_alloc_cache *nc;
	struct sk_buff *skb;
	bool pfmemalloc;
	void *data;

	DEBUG_NET_WARN_ON_ONCE(!in_softirq());
	len += NET_SKB_PAD + NET_IP_ALIGN;

	/* If requested length is either too small or too big,
	 * we use kmalloc() for skb->head allocation.
	 * When the small frag allocator is available, prefer it over kmalloc
	 * for small fragments
	 */
	if ((!NAPI_HAS_SMALL_PAGE_FRAG && len <= SKB_WITH_OVERHEAD(1024)) ||
	    len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
	    (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
		skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX | SKB_ALLOC_NAPI,
				  NUMA_NO_NODE);
		if (!skb)
			goto skb_fail;
		goto skb_success;
	}

	if (sk_memalloc_socks())
		gfp_mask |= __GFP_MEMALLOC;

	local_lock_nested_bh(&napi_alloc_cache.bh_lock);
	nc = this_cpu_ptr(&napi_alloc_cache);
	if (NAPI_HAS_SMALL_PAGE_FRAG && len <= SKB_WITH_OVERHEAD(1024)) {
		/* we are artificially inflating the allocation size, but
		 * that is not as bad as it may look like, as:
		 * - 'len' less than GRO_MAX_HEAD makes little sense
		 * - On most systems, larger 'len' values lead to fragment
		 *   size above 512 bytes
		 * - kmalloc would use the kmalloc-1k slab for such values
		 * - Builds with smaller GRO_MAX_HEAD will very likely do
		 *   little networking, as that implies no WiFi and no
		 *   tunnels support, and 32 bits arches.
		 */
		len = SZ_1K;

		data = page_frag_alloc_1k(&nc->page_small, gfp_mask);
		pfmemalloc = NAPI_SMALL_PAGE_PFMEMALLOC(nc->page_small);
	} else {
		len = SKB_HEAD_ALIGN(len);

		data = page_frag_alloc(&nc->page, len, gfp_mask);
		pfmemalloc = nc->page.pfmemalloc;
	}
	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);

	if (unlikely(!data))
		return NULL;

	skb = __napi_build_skb(data, len);
	if (unlikely(!skb)) {
		skb_free_frag(data);
		return NULL;
	}

	if (pfmemalloc)
		skb->pfmemalloc = 1;
	skb->head_frag = 1;

skb_success:
	skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
	skb->dev = napi->dev;

skb_fail:
	return skb;
}
EXPORT_SYMBOL(napi_alloc_skb);

void skb_add_rx_frag_netmem(struct sk_buff *skb, int i, netmem_ref netmem,
			    int off, int size, unsigned int truesize)
{
	DEBUG_NET_WARN_ON_ONCE(size > truesize);

	skb_fill_netmem_desc(skb, i, netmem, off, size);
	skb->len += size;
	skb->data_len += size;
	skb->truesize += truesize;
}
EXPORT_SYMBOL(skb_add_rx_frag_netmem);

void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
			  unsigned int truesize)
{
	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

	DEBUG_NET_WARN_ON_ONCE(size > truesize);

	skb_frag_size_add(frag, size);
	skb->len += size;
	skb->data_len += size;
	skb->truesize += truesize;
}
EXPORT_SYMBOL(skb_coalesce_rx_frag);

static void skb_drop_list(struct sk_buff **listp)
{
	kfree_skb_list(*listp);
	*listp = NULL;
}

static inline void skb_drop_fraglist(struct sk_buff *skb)
{
	skb_drop_list(&skb_shinfo(skb)->frag_list);
}

static void skb_clone_fraglist(struct sk_buff *skb)
{
	struct sk_buff *list;

	skb_walk_frags(skb, list)
		skb_get(list);
}

static bool is_pp_page(struct page *page)
{
	return (page->pp_magic & ~0x3UL) == PP_SIGNATURE;
}

int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb,
		    unsigned int headroom)
{
#if IS_ENABLED(CONFIG_PAGE_POOL)
	u32 size, truesize, len, max_head_size, off;
	struct sk_buff *skb = *pskb, *nskb;
	int err, i, head_off;
	void *data;

	/* XDP does not support fraglist so we need to linearize
	 * the skb.
	 */
	if (skb_has_frag_list(skb))
		return -EOPNOTSUPP;

	max_head_size = SKB_WITH_OVERHEAD(PAGE_SIZE - headroom);
	if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE)
		return -ENOMEM;

	size = min_t(u32, skb->len, max_head_size);
	truesize = SKB_HEAD_ALIGN(size) + headroom;
	data = page_pool_dev_alloc_va(pool, &truesize);
	if (!data)
		return -ENOMEM;

	nskb = napi_build_skb(data, truesize);
	if (!nskb) {
		page_pool_free_va(pool, data, true);
		return -ENOMEM;
	}

	skb_reserve(nskb, headroom);
	skb_copy_header(nskb, skb);
	skb_mark_for_recycle(nskb);

	err = skb_copy_bits(skb, 0, nskb->data, size);
	if (err) {
		consume_skb(nskb);
		return err;
	}
	skb_put(nskb, size);

	head_off = skb_headroom(nskb) - skb_headroom(skb);
	skb_headers_offset_update(nskb, head_off);

	off = size;
	len = skb->len - off;
	for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) {
		struct page *page;
		u32 page_off;

		size = min_t(u32, len, PAGE_SIZE);
		truesize = size;

		page = page_pool_dev_alloc(pool, &page_off, &truesize);
		if (!page) {
			consume_skb(nskb);
			return -ENOMEM;
		}

		skb_add_rx_frag(nskb, i, page, page_off, size, truesize);
		err = skb_copy_bits(skb, off, page_address(page) + page_off,
				    size);
		if (err) {
			consume_skb(nskb);
			return err;
		}

		len -= size;
		off += size;
	}

	consume_skb(skb);
	*pskb = nskb;

	return 0;
#else
	return -EOPNOTSUPP;
#endif
}
EXPORT_SYMBOL(skb_pp_cow_data);

int skb_cow_data_for_xdp(struct page_pool *pool, struct sk_buff **pskb,
			 struct bpf_prog *prog)
{
	if (!prog->aux->xdp_has_frags)
		return -EINVAL;

	return skb_pp_cow_data(pool, pskb, XDP_PACKET_HEADROOM);
}
EXPORT_SYMBOL(skb_cow_data_for_xdp);

#if IS_ENABLED(CONFIG_PAGE_POOL)
bool napi_pp_put_page(netmem_ref netmem)
{
	struct page *page = netmem_to_page(netmem);

	page = compound_head(page);

	/* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
	 * in order to preserve any existing bits, such as bit 0 for the
	 * head page of compound page and bit 1 for pfmemalloc page, so
	 * mask those bits for freeing side when doing below checking,
	 * and page_is_pfmemalloc() is checked in __page_pool_put_page()
	 * to avoid recycling the pfmemalloc page.
	 */
	if (unlikely(!is_pp_page(page)))
		return false;

	page_pool_put_full_netmem(page->pp, page_to_netmem(page), false);

	return true;
}
EXPORT_SYMBOL(napi_pp_put_page);
#endif

static bool skb_pp_recycle(struct sk_buff *skb, void *data)
{
	if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
		return false;
	return napi_pp_put_page(page_to_netmem(virt_to_page(data)));
}

/**
 * skb_pp_frag_ref() - Increase fragment references of a page pool aware skb
 * @skb:	page pool aware skb
 *
 * Increase the fragment reference count (pp_ref_count) of a skb. This is
 * intended to gain fragment references only for page pool aware skbs,
 * i.e. when skb->pp_recycle is true, and not for fragments in a
 * non-pp-recycling skb. It has a fallback to increase references on normal
 * pages, as page pool aware skbs may also have normal page fragments.
 */
static int skb_pp_frag_ref(struct sk_buff *skb)
{
	struct skb_shared_info *shinfo;
	struct page *head_page;
	int i;

	if (!skb->pp_recycle)
		return -EINVAL;

	shinfo = skb_shinfo(skb);

	for (i = 0; i < shinfo->nr_frags; i++) {
		head_page = compound_head(skb_frag_page(&shinfo->frags[i]));
		if (likely(is_pp_page(head_page)))
			page_pool_ref_page(head_page);
		else
			page_ref_inc(head_page);
	}
	return 0;
}

static void skb_kfree_head(void *head, unsigned int end_offset)
{
	if (end_offset == SKB_SMALL_HEAD_HEADROOM)
		kmem_cache_free(net_hotdata.skb_small_head_cache, head);
	else
		kfree(head);
}

static void skb_free_head(struct sk_buff *skb)
{
	unsigned char *head = skb->head;

	if (skb->head_frag) {
		if (skb_pp_recycle(skb, head))
			return;
		skb_free_frag(head);
	} else {
		skb_kfree_head(head, skb_end_offset(skb));
	}
}

static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);
	int i;

	if (!skb_data_unref(skb, shinfo))
		goto exit;

	if (skb_zcopy(skb)) {
		bool skip_unref = shinfo->flags & SKBFL_MANAGED_FRAG_REFS;

		skb_zcopy_clear(skb, true);
		if (skip_unref)
			goto free_head;
	}

	for (i = 0; i < shinfo->nr_frags; i++)
		__skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);

free_head:
	if (shinfo->frag_list)
		kfree_skb_list_reason(shinfo->frag_list, reason);

	skb_free_head(skb);
exit:
	/* When we clone an SKB we copy the reycling bit. The pp_recycle
	 * bit is only set on the head though, so in order to avoid races
	 * while trying to recycle fragments on __skb_frag_unref() we need
	 * to make one SKB responsible for triggering the recycle path.
	 * So disable the recycling bit if an SKB is cloned and we have
	 * additional references to the fragmented part of the SKB.
	 * Eventually the last SKB will have the recycling bit set and it's
	 * dataref set to 0, which will trigger the recycling
	 */
	skb->pp_recycle = 0;
}

/*
 *	Free an skbuff by memory without cleaning the state.
 */
static void kfree_skbmem(struct sk_buff *skb)
{
	struct sk_buff_fclones *fclones;

	switch (skb->fclone) {
	case SKB_FCLONE_UNAVAILABLE:
		kmem_cache_free(net_hotdata.skbuff_cache, skb);
		return;

	case SKB_FCLONE_ORIG:
		fclones = container_of(skb, struct sk_buff_fclones, skb1);

		/* We usually free the clone (TX completion) before original skb
		 * This test would have no chance to be true for the clone,
		 * while here, branch prediction will be good.
		 */
		if (refcount_read(&fclones->fclone_ref) == 1)
			goto fastpath;
		break;

	default: /* SKB_FCLONE_CLONE */
		fclones = container_of(skb, struct sk_buff_fclones, skb2);
		break;
	}
	if (!refcount_dec_and_test(&fclones->fclone_ref))
		return;
fastpath:
	kmem_cache_free(net_hotdata.skbuff_fclone_cache, fclones);
}

void skb_release_head_state(struct sk_buff *skb)
{
	skb_dst_drop(skb);
	if (skb->destructor) {
		DEBUG_NET_WARN_ON_ONCE(in_hardirq());
		skb->destructor(skb);
	}
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
	nf_conntrack_put(skb_nfct(skb));
#endif
	skb_ext_put(skb);
}

/* Free everything but the sk_buff shell. */
static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason)
{
	skb_release_head_state(skb);
	if (likely(skb->head))
		skb_release_data(skb, reason);
}

/**
 *	__kfree_skb - private function
 *	@skb: buffer
 *
 *	Free an sk_buff. Release anything attached to the buffer.
 *	Clean the state. This is an internal helper function. Users should
 *	always call kfree_skb
 */

void __kfree_skb(struct sk_buff *skb)
{
	skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED);
	kfree_skbmem(skb);
}
EXPORT_SYMBOL(__kfree_skb);

static __always_inline
bool __sk_skb_reason_drop(struct sock *sk, struct sk_buff *skb,
			  enum skb_drop_reason reason)
{
	if (unlikely(!skb_unref(skb)))
		return false;

	DEBUG_NET_WARN_ON_ONCE(reason == SKB_NOT_DROPPED_YET ||
			       u32_get_bits(reason,
					    SKB_DROP_REASON_SUBSYS_MASK) >=
				SKB_DROP_REASON_SUBSYS_NUM);

	if (reason == SKB_CONSUMED)
		trace_consume_skb(skb, __builtin_return_address(0));
	else
		trace_kfree_skb(skb, __builtin_return_address(0), reason, sk);
	return true;
}

/**
 *	sk_skb_reason_drop - free an sk_buff with special reason
 *	@sk: the socket to receive @skb, or NULL if not applicable
 *	@skb: buffer to free
 *	@reason: reason why this skb is dropped
 *
 *	Drop a reference to the buffer and free it if the usage count has hit
 *	zero. Meanwhile, pass the receiving socket and drop reason to
 *	'kfree_skb' tracepoint.
 */
void __fix_address
sk_skb_reason_drop(struct sock *sk, struct sk_buff *skb, enum skb_drop_reason reason)
{
	if (__sk_skb_reason_drop(sk, skb, reason))
		__kfree_skb(skb);
}
EXPORT_SYMBOL(sk_skb_reason_drop);

#define KFREE_SKB_BULK_SIZE	16

struct skb_free_array {
	unsigned int skb_count;
	void *skb_array[KFREE_SKB_BULK_SIZE];
};

static void kfree_skb_add_bulk(struct sk_buff *skb,
			       struct skb_free_array *sa,
			       enum skb_drop_reason reason)
{
	/* if SKB is a clone, don't handle this case */
	if (unlikely(skb->fclone != SKB_FCLONE_UNAVAILABLE)) {
		__kfree_skb(skb);
		return;
	}

	skb_release_all(skb, reason);
	sa->skb_array[sa->skb_count++] = skb;

	if (unlikely(sa->skb_count == KFREE_SKB_BULK_SIZE)) {
		kmem_cache_free_bulk(net_hotdata.skbuff_cache, KFREE_SKB_BULK_SIZE,
				     sa->skb_array);
		sa->skb_count = 0;
	}
}

void __fix_address
kfree_skb_list_reason(struct sk_buff *segs, enum skb_drop_reason reason)
{
	struct skb_free_array sa;

	sa.skb_count = 0;

	while (segs) {
		struct sk_buff *next = segs->next;

		if (__sk_skb_reason_drop(NULL, segs, reason)) {
			skb_poison_list(segs);
			kfree_skb_add_bulk(segs, &sa, reason);
		}

		segs = next;
	}

	if (sa.skb_count)
		kmem_cache_free_bulk(net_hotdata.skbuff_cache, sa.skb_count, sa.skb_array);
}
EXPORT_SYMBOL(kfree_skb_list_reason);

/* Dump skb information and contents.
 *
 * Must only be called from net_ratelimit()-ed paths.
 *
 * Dumps whole packets if full_pkt, only headers otherwise.
 */
void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt)
{
	struct skb_shared_info *sh = skb_shinfo(skb);
	struct net_device *dev = skb->dev;
	struct sock *sk = skb->sk;
	struct sk_buff *list_skb;
	bool has_mac, has_trans;
	int headroom, tailroom;
	int i, len, seg_len;

	if (full_pkt)
		len = skb->len;
	else
		len = min_t(int, skb->len, MAX_HEADER + 128);

	headroom = skb_headroom(skb);
	tailroom = skb_tailroom(skb);

	has_mac = skb_mac_header_was_set(skb);
	has_trans = skb_transport_header_was_set(skb);

	printk("%sskb len=%u headroom=%u headlen=%u tailroom=%u\n"
	       "mac=(%d,%d) mac_len=%u net=(%d,%d) trans=%d\n"
	       "shinfo(txflags=%u nr_frags=%u gso(size=%hu type=%u segs=%hu))\n"
	       "csum(0x%x start=%u offset=%u ip_summed=%u complete_sw=%u valid=%u level=%u)\n"
	       "hash(0x%x sw=%u l4=%u) proto=0x%04x pkttype=%u iif=%d\n"
	       "priority=0x%x mark=0x%x alloc_cpu=%u vlan_all=0x%x\n"
	       "encapsulation=%d inner(proto=0x%04x, mac=%u, net=%u, trans=%u)\n",
	       level, skb->len, headroom, skb_headlen(skb), tailroom,
	       has_mac ? skb->mac_header : -1,
	       has_mac ? skb_mac_header_len(skb) : -1,
	       skb->mac_len,
	       skb->network_header,
	       has_trans ? skb_network_header_len(skb) : -1,
	       has_trans ? skb->transport_header : -1,
	       sh->tx_flags, sh->nr_frags,
	       sh->gso_size, sh->gso_type, sh->gso_segs,
	       skb->csum, skb->csum_start, skb->csum_offset, skb->ip_summed,
	       skb->csum_complete_sw, skb->csum_valid, skb->csum_level,
	       skb->hash, skb->sw_hash, skb->l4_hash,
	       ntohs(skb->protocol), skb->pkt_type, skb->skb_iif,
	       skb->priority, skb->mark, skb->alloc_cpu, skb->vlan_all,
	       skb->encapsulation, skb->inner_protocol, skb->inner_mac_header,
	       skb->inner_network_header, skb->inner_transport_header);

	if (dev)
		printk("%sdev name=%s feat=%pNF\n",
		       level, dev->name, &dev->features);
	if (sk)
		printk("%ssk family=%hu type=%u proto=%u\n",
		       level, sk->sk_family, sk->sk_type, sk->sk_protocol);

	if (full_pkt && headroom)
		print_hex_dump(level, "skb headroom: ", DUMP_PREFIX_OFFSET,
			       16, 1, skb->head, headroom, false);

	seg_len = min_t(int, skb_headlen(skb), len);
	if (seg_len)
		print_hex_dump(level, "skb linear:   ", DUMP_PREFIX_OFFSET,
			       16, 1, skb->data, seg_len, false);
	len -= seg_len;

	if (full_pkt && tailroom)
		print_hex_dump(level, "skb tailroom: ", DUMP_PREFIX_OFFSET,
			       16, 1, skb_tail_pointer(skb), tailroom, false);

	for (i = 0; len && i < skb_shinfo(skb)->nr_frags; i++) {
		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
		u32 p_off, p_len, copied;
		struct page *p;
		u8 *vaddr;

		skb_frag_foreach_page(frag, skb_frag_off(frag),
				      skb_frag_size(frag), p, p_off, p_len,
				      copied) {
			seg_len = min_t(int, p_len, len);
			vaddr = kmap_atomic(p);
			print_hex_dump(level, "skb frag:     ",
				       DUMP_PREFIX_OFFSET,
				       16, 1, vaddr + p_off, seg_len, false);
			kunmap_atomic(vaddr);
			len -= seg_len;
			if (!len)
				break;
		}
	}

	if (full_pkt && skb_has_frag_list(skb)) {
		printk("skb fraglist:\n");
		skb_walk_frags(skb, list_skb)
			skb_dump(level, list_skb, true);
	}
}
EXPORT_SYMBOL(skb_dump);

/**
 *	skb_tx_error - report an sk_buff xmit error
 *	@skb: buffer that triggered an error
 *
 *	Report xmit error if a device callback is tracking this skb.
 *	skb must be freed afterwards.
 */
void skb_tx_error(struct sk_buff *skb)
{
	if (skb) {
		skb_zcopy_downgrade_managed(skb);
		skb_zcopy_clear(skb, true);
	}
}
EXPORT_SYMBOL(skb_tx_error);

#ifdef CONFIG_TRACEPOINTS
/**
 *	consume_skb - free an skbuff
 *	@skb: buffer to free
 *
 *	Drop a ref to the buffer and free it if the usage count has hit zero
 *	Functions identically to kfree_skb, but kfree_skb assumes that the frame
 *	is being dropped after a failure and notes that
 */
void consume_skb(struct sk_buff *skb)
{
	if (!skb_unref(skb))
		return;

	trace_consume_skb(skb, __builtin_return_address(0));
	__kfree_skb(skb);
}
EXPORT_SYMBOL(consume_skb);
#endif

/**
 *	__consume_stateless_skb - free an skbuff, assuming it is stateless
 *	@skb: buffer to free
 *
 *	Alike consume_skb(), but this variant assumes that this is the last
 *	skb reference and all the head states have been already dropped
 */
void __consume_stateless_skb(struct sk_buff *skb)
{
	trace_consume_skb(skb, __builtin_return_address(0));
	skb_release_data(skb, SKB_CONSUMED);
	kfree_skbmem(skb);
}

static void napi_skb_cache_put(struct sk_buff *skb)
{
	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
	u32 i;

	if (!kasan_mempool_poison_object(skb))
		return;

	local_lock_nested_bh(&napi_alloc_cache.bh_lock);
	nc->skb_cache[nc->skb_count++] = skb;

	if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
		for (i = NAPI_SKB_CACHE_HALF; i < NAPI_SKB_CACHE_SIZE; i++)
			kasan_mempool_unpoison_object(nc->skb_cache[i],
						kmem_cache_size(net_hotdata.skbuff_cache));

		kmem_cache_free_bulk(net_hotdata.skbuff_cache, NAPI_SKB_CACHE_HALF,
				     nc->skb_cache + NAPI_SKB_CACHE_HALF);
		nc->skb_count = NAPI_SKB_CACHE_HALF;
	}
	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
}

void __napi_kfree_skb(struct sk_buff *skb, enum skb_drop_reason reason)
{
	skb_release_all(skb, reason);
	napi_skb_cache_put(skb);
}

void napi_skb_free_stolen_head(struct sk_buff *skb)
{
	if (unlikely(skb->slow_gro)) {
		nf_reset_ct(skb);
		skb_dst_drop(skb);
		skb_ext_put(skb);
		skb_orphan(skb);
		skb->slow_gro = 0;
	}
	napi_skb_cache_put(skb);
}

void napi_consume_skb(struct sk_buff *skb, int budget)
{
	/* Zero budget indicate non-NAPI context called us, like netpoll */
	if (unlikely(!budget)) {
		dev_consume_skb_any(skb);
		return;
	}

	DEBUG_NET_WARN_ON_ONCE(!in_softirq());

	if (!skb_unref(skb))
		return;

	/* if reaching here SKB is ready to free */
	trace_consume_skb(skb, __builtin_return_address(0));

	/* if SKB is a clone, don't handle this case */
	if (skb->fclone != SKB_FCLONE_UNAVAILABLE) {
		__kfree_skb(skb);
		return;
	}

	skb_release_all(skb, SKB_CONSUMED);
	napi_skb_cache_put(skb);
}
EXPORT_SYMBOL(napi_consume_skb);

/* Make sure a field is contained by headers group */
#define CHECK_SKB_FIELD(field) \
	BUILD_BUG_ON(offsetof(struct sk_buff, field) !=		\
		     offsetof(struct sk_buff, headers.field));	\

static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
{
	new->tstamp		= old->tstamp;
	/* We do not copy old->sk */
	new->dev		= old->dev;
	memcpy(new->cb, old->cb, sizeof(old->cb));
	skb_dst_copy(new, old);
	__skb_ext_copy(new, old);
	__nf_copy(new, old, false);

	/* Note : this field could be in the headers group.
	 * It is not yet because we do not want to have a 16 bit hole
	 */
	new->queue_mapping = old->queue_mapping;

	memcpy(&new->headers, &old->headers, sizeof(new->headers));
	CHECK_SKB_FIELD(protocol);
	CHECK_SKB_FIELD(csum);
	CHECK_SKB_FIELD(hash);
	CHECK_SKB_FIELD(priority);
	CHECK_SKB_FIELD(skb_iif);
	CHECK_SKB_FIELD(vlan_proto);
	CHECK_SKB_FIELD(vlan_tci);
	CHECK_SKB_FIELD(transport_header);
	CHECK_SKB_FIELD(network_header);
	CHECK_SKB_FIELD(mac_header);
	CHECK_SKB_FIELD(inner_protocol);
	CHECK_SKB_FIELD(inner_transport_header);
	CHECK_SKB_FIELD(inner_network_header);
	CHECK_SKB_FIELD(inner_mac_header);
	CHECK_SKB_FIELD(mark);
#ifdef CONFIG_NETWORK_SECMARK
	CHECK_SKB_FIELD(secmark);
#endif
#ifdef CONFIG_NET_RX_BUSY_POLL
	CHECK_SKB_FIELD(napi_id);
#endif
	CHECK_SKB_FIELD(alloc_cpu);
#ifdef CONFIG_XPS
	CHECK_SKB_FIELD(sender_cpu);
#endif
#ifdef CONFIG_NET_SCHED
	CHECK_SKB_FIELD(tc_index);
#endif

}

/*
 * You should not add any new code to this function.  Add it to
 * __copy_skb_header above instead.
 */
static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
{
#define C(x) n->x = skb->x

	n->next = n->prev = NULL;
	n->sk = NULL;
	__copy_skb_header(n, skb);

	C(len);
	C(data_len);
	C(mac_len);
	n->hdr_len = skb->nohdr ? skb_headroom(skb) : skb->hdr_len;
	n->cloned = 1;
	n->nohdr = 0;
	n->peeked = 0;
	C(pfmemalloc);
	C(pp_recycle);
	n->destructor = NULL;
	C(tail);
	C(end);
	C(head);
	C(head_frag);
	C(data);
	C(truesize);
	refcount_set(&n->users, 1);

	atomic_inc(&(skb_shinfo(skb)->dataref));
	skb->cloned = 1;

	return n;
#undef C
}

/**
 * alloc_skb_for_msg() - allocate sk_buff to wrap frag list forming a msg
 * @first: first sk_buff of the msg
 */
struct sk_buff *alloc_skb_for_msg(struct sk_buff *first)
{
	struct sk_buff *n;

	n = alloc_skb(0, GFP_ATOMIC);
	if (!n)
		return NULL;

	n->len = first->len;
	n->data_len = first->len;
	n->truesize = first->truesize;

	skb_shinfo(n)->frag_list = first;

	__copy_skb_header(n, first);
	n->destructor = NULL;

	return n;
}
EXPORT_SYMBOL_GPL(alloc_skb_for_msg);

/**
 *	skb_morph	-	morph one skb into another
 *	@dst: the skb to receive the contents
 *	@src: the skb to supply the contents
 *
 *	This is identical to skb_clone except that the target skb is
 *	supplied by the user.
 *
 *	The target skb is returned upon exit.
 */
struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
{
	skb_release_all(dst, SKB_CONSUMED);
	return __skb_clone(dst, src);
}
EXPORT_SYMBOL_GPL(skb_morph);

int mm_account_pinned_pages(struct mmpin *mmp, size_t size)
{
	unsigned long max_pg, num_pg, new_pg, old_pg, rlim;
	struct user_struct *user;

	if (capable(CAP_IPC_LOCK) || !size)
		return 0;

	rlim = rlimit(RLIMIT_MEMLOCK);
	if (rlim == RLIM_INFINITY)
		return 0;

	num_pg = (size >> PAGE_SHIFT) + 2;	/* worst case */
	max_pg = rlim >> PAGE_SHIFT;
	user = mmp->user ? : current_user();

	old_pg = atomic_long_read(&user->locked_vm);
	do {
		new_pg = old_pg + num_pg;
		if (new_pg > max_pg)
			return -ENOBUFS;
	} while (!atomic_long_try_cmpxchg(&user->locked_vm, &old_pg, new_pg));

	if (!mmp->user) {
		mmp->user = get_uid(user);
		mmp->num_pg = num_pg;
	} else {
		mmp->num_pg += num_pg;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(mm_account_pinned_pages);

void mm_unaccount_pinned_pages(struct mmpin *mmp)
{
	if (mmp->user) {
		atomic_long_sub(mmp->num_pg, &mmp->user->locked_vm);
		free_uid(mmp->user);
	}
}
EXPORT_SYMBOL_GPL(mm_unaccount_pinned_pages);

static struct ubuf_info *msg_zerocopy_alloc(struct sock *sk, size_t size)
{
	struct ubuf_info_msgzc *uarg;
	struct sk_buff *skb;

	WARN_ON_ONCE(!in_task());

	skb = sock_omalloc(sk, 0, GFP_KERNEL);
	if (!skb)
		return NULL;

	BUILD_BUG_ON(sizeof(*uarg) > sizeof(skb->cb));
	uarg = (void *)skb->cb;
	uarg->mmp.user = NULL;

	if (mm_account_pinned_pages(&uarg->mmp, size)) {
		kfree_skb(skb);
		return NULL;
	}

	uarg->ubuf.ops = &msg_zerocopy_ubuf_ops;
	uarg->id = ((u32)atomic_inc_return(&sk->sk_zckey)) - 1;
	uarg->len = 1;
	uarg->bytelen = size;
	uarg->zerocopy = 1;
	uarg->ubuf.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
	refcount_set(&uarg->ubuf.refcnt, 1);
	sock_hold(sk);

	return &uarg->ubuf;
}

static inline struct sk_buff *skb_from_uarg(struct ubuf_info_msgzc *uarg)
{
	return container_of((void *)uarg, struct sk_buff, cb);
}

struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
				       struct ubuf_info *uarg)
{
	if (uarg) {
		struct ubuf_info_msgzc *uarg_zc;
		const u32 byte_limit = 1 << 19;		/* limit to a few TSO */
		u32 bytelen, next;

		/* there might be non MSG_ZEROCOPY users */
		if (uarg->ops != &msg_zerocopy_ubuf_ops)
			return NULL;

		/* realloc only when socket is locked (TCP, UDP cork),
		 * so uarg->len and sk_zckey access is serialized
		 */
		if (!sock_owned_by_user(sk)) {
			WARN_ON_ONCE(1);
			return NULL;
		}

		uarg_zc = uarg_to_msgzc(uarg);
		bytelen = uarg_zc->bytelen + size;
		if (uarg_zc->len == USHRT_MAX - 1 || bytelen > byte_limit) {
			/* TCP can create new skb to attach new uarg */
			if (sk->sk_type == SOCK_STREAM)
				goto new_alloc;
			return NULL;
		}

		next = (u32)atomic_read(&sk->sk_zckey);
		if ((u32)(uarg_zc->id + uarg_zc->len) == next) {
			if (mm_account_pinned_pages(&uarg_zc->mmp, size))
				return NULL;
			uarg_zc->len++;
			uarg_zc->bytelen = bytelen;
			atomic_set(&sk->sk_zckey, ++next);

			/* no extra ref when appending to datagram (MSG_MORE) */
			if (sk->sk_type == SOCK_STREAM)
				net_zcopy_get(uarg);

			return uarg;
		}
	}

new_alloc:
	return msg_zerocopy_alloc(sk, size);
}
EXPORT_SYMBOL_GPL(msg_zerocopy_realloc);

static bool skb_zerocopy_notify_extend(struct sk_buff *skb, u32 lo, u16 len)
{
	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
	u32 old_lo, old_hi;
	u64 sum_len;

	old_lo = serr->ee.ee_info;
	old_hi = serr->ee.ee_data;
	sum_len = old_hi - old_lo + 1ULL + len;

	if (sum_len >= (1ULL << 32))
		return false;

	if (lo != old_hi + 1)
		return false;

	serr->ee.ee_data += len;
	return true;
}

static void __msg_zerocopy_callback(struct ubuf_info_msgzc *uarg)
{
	struct sk_buff *tail, *skb = skb_from_uarg(uarg);
	struct sock_exterr_skb *serr;
	struct sock *sk = skb->sk;
	struct sk_buff_head *q;
	unsigned long flags;
	bool is_zerocopy;
	u32 lo, hi;
	u16 len;

	mm_unaccount_pinned_pages(&uarg->mmp);

	/* if !len, there was only 1 call, and it was aborted
	 * so do not queue a completion notification
	 */
	if (!uarg->len || sock_flag(sk, SOCK_DEAD))
		goto release;

	len = uarg->len;
	lo = uarg->id;
	hi = uarg->id + len - 1;
	is_zerocopy = uarg->zerocopy;

	serr = SKB_EXT_ERR(skb);
	memset(serr, 0, sizeof(*serr));
	serr->ee.ee_errno = 0;
	serr->ee.ee_origin = SO_EE_ORIGIN_ZEROCOPY;
	serr->ee.ee_data = hi;
	serr->ee.ee_info = lo;
	if (!is_zerocopy)
		serr->ee.ee_code |= SO_EE_CODE_ZEROCOPY_COPIED;

	q = &sk->sk_error_queue;
	spin_lock_irqsave(&q->lock, flags);
	tail = skb_peek_tail(q);
	if (!tail || SKB_EXT_ERR(tail)->ee.ee_origin != SO_EE_ORIGIN_ZEROCOPY ||
	    !skb_zerocopy_notify_extend(tail, lo, len)) {
		__skb_queue_tail(q, skb);
		skb = NULL;
	}
	spin_unlock_irqrestore(&q->lock, flags);

	sk_error_report(sk);

release:
	consume_skb(skb);
	sock_put(sk);
}

static void msg_zerocopy_complete(struct sk_buff *skb, struct ubuf_info *uarg,
				  bool success)
{
	struct ubuf_info_msgzc *uarg_zc = uarg_to_msgzc(uarg);

	uarg_zc->zerocopy = uarg_zc->zerocopy & success;

	if (refcount_dec_and_test(&uarg->refcnt))
		__msg_zerocopy_callback(uarg_zc);
}

void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
{
	struct sock *sk = skb_from_uarg(uarg_to_msgzc(uarg))->sk;

	atomic_dec(&sk->sk_zckey);
	uarg_to_msgzc(uarg)->len--;

	if (have_uref)
		msg_zerocopy_complete(NULL, uarg, true);
}
EXPORT_SYMBOL_GPL(msg_zerocopy_put_abort);

const struct ubuf_info_ops msg_zerocopy_ubuf_ops = {
	.complete = msg_zerocopy_complete,
};
EXPORT_SYMBOL_GPL(msg_zerocopy_ubuf_ops);

int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
			     struct msghdr *msg, int len,
			     struct ubuf_info *uarg)
{
	int err, orig_len = skb->len;

	if (uarg->ops->link_skb) {
		err = uarg->ops->link_skb(skb, uarg);
		if (err)
			return err;
	} else {
		struct ubuf_info *orig_uarg = skb_zcopy(skb);

		/* An skb can only point to one uarg. This edge case happens
		 * when TCP appends to an skb, but zerocopy_realloc triggered
		 * a new alloc.
		 */
		if (orig_uarg && uarg != orig_uarg)
			return -EEXIST;
	}

	err = __zerocopy_sg_from_iter(msg, sk, skb, &msg->msg_iter, len);
	if (err == -EFAULT || (err == -EMSGSIZE && skb->len == orig_len)) {
		struct sock *save_sk = skb->sk;

		/* Streams do not free skb on error. Reset to prev state. */
		iov_iter_revert(&msg->msg_iter, skb->len - orig_len);
		skb->sk = sk;
		___pskb_trim(skb, orig_len);
		skb->sk = save_sk;
		return err;
	}

	skb_zcopy_set(skb, uarg, NULL);
	return skb->len - orig_len;
}
EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);

void __skb_zcopy_downgrade_managed(struct sk_buff *skb)
{
	int i;

	skb_shinfo(skb)->flags &= ~SKBFL_MANAGED_FRAG_REFS;
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
		skb_frag_ref(skb, i);
}
EXPORT_SYMBOL_GPL(__skb_zcopy_downgrade_managed);

static int skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig,
			      gfp_t gfp_mask)
{
	if (skb_zcopy(orig)) {
		if (skb_zcopy(nskb)) {
			/* !gfp_mask callers are verified to !skb_zcopy(nskb) */
			if (!gfp_mask) {
				WARN_ON_ONCE(1);
				return -ENOMEM;
			}
			if (skb_uarg(nskb) == skb_uarg(orig))
				return 0;
			if (skb_copy_ubufs(nskb, GFP_ATOMIC))
				return -EIO;
		}
		skb_zcopy_set(nskb, skb_uarg(orig), NULL);
	}
	return 0;
}

/**
 *	skb_copy_ubufs	-	copy userspace skb frags buffers to kernel
 *	@skb: the skb to modify
 *	@gfp_mask: allocation priority
 *
 *	This must be called on skb with SKBFL_ZEROCOPY_ENABLE.
 *	It will copy all frags into kernel and drop the reference
 *	to userspace pages.
 *
 *	If this function is called from an interrupt gfp_mask() must be
 *	%GFP_ATOMIC.
 *
 *	Returns 0 on success or a negative error code on failure
 *	to allocate kernel memory to copy to.
 */
int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
{
	int num_frags = skb_shinfo(skb)->nr_frags;
	struct page *page, *head = NULL;
	int i, order, psize, new_frags;
	u32 d_off;

	if (skb_shared(skb) || skb_unclone(skb, gfp_mask))
		return -EINVAL;

	if (!num_frags)
		goto release;

	/* We might have to allocate high order pages, so compute what minimum
	 * page order is needed.
	 */
	order = 0;
	while ((PAGE_SIZE << order) * MAX_SKB_FRAGS < __skb_pagelen(skb))
		order++;
	psize = (PAGE_SIZE << order);

	new_frags = (__skb_pagelen(skb) + psize - 1) >> (PAGE_SHIFT + order);
	for (i = 0; i < new_frags; i++) {
		page = alloc_pages(gfp_mask | __GFP_COMP, order);
		if (!page) {
			while (head) {
				struct page *next = (struct page *)page_private(head);
				put_page(head);
				head = next;
			}
			return -ENOMEM;
		}
		set_page_private(page, (unsigned long)head);
		head = page;
	}

	page = head;
	d_off = 0;
	for (i = 0; i < num_frags; i++) {
		skb_frag_t *f = &skb_shinfo(skb)->frags[i];
		u32 p_off, p_len, copied;
		struct page *p;
		u8 *vaddr;

		skb_frag_foreach_page(f, skb_frag_off(f), skb_frag_size(f),
				      p, p_off, p_len, copied) {
			u32 copy, done = 0;
			vaddr = kmap_atomic(p);

			while (done < p_len) {
				if (d_off == psize) {
					d_off = 0;
					page = (struct page *)page_private(page);
				}
				copy = min_t(u32, psize - d_off, p_len - done);
				memcpy(page_address(page) + d_off,
				       vaddr + p_off + done, copy);
				done += copy;
				d_off += copy;
			}
			kunmap_atomic(vaddr);
		}
	}

	/* skb frags release userspace buffers */
	for (i = 0; i < num_frags; i++)
		skb_frag_unref(skb, i);

	/* skb frags point to kernel buffers */
	for (i = 0; i < new_frags - 1; i++) {
		__skb_fill_netmem_desc(skb, i, page_to_netmem(head), 0, psize);
		head = (struct page *)page_private(head);
	}
	__skb_fill_netmem_desc(skb, new_frags - 1, page_to_netmem(head), 0,
			       d_off);
	skb_shinfo(skb)->nr_frags = new_frags;

release:
	skb_zcopy_clear(skb, false);
	return 0;
}
EXPORT_SYMBOL_GPL(skb_copy_ubufs);

/**
 *	skb_clone	-	duplicate an sk_buff
 *	@skb: buffer to clone
 *	@gfp_mask: allocation priority
 *
 *	Duplicate an &sk_buff. The new one is not owned by a socket. Both
 *	copies share the same packet data but not structure. The new
 *	buffer has a reference count of 1. If the allocation fails the
 *	function returns %NULL otherwise the new buffer is returned.
 *
 *	If this function is called from an interrupt gfp_mask() must be
 *	%GFP_ATOMIC.
 */

struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
{
	struct sk_buff_fclones *fclones = container_of(skb,
						       struct sk_buff_fclones,
						       skb1);
	struct sk_buff *n;

	if (skb_orphan_frags(skb, gfp_mask))
		return NULL;

	if (skb->fclone == SKB_FCLONE_ORIG &&
	    refcount_read(&fclones->fclone_ref) == 1) {
		n = &fclones->skb2;
		refcount_set(&fclones->fclone_ref, 2);
		n->fclone = SKB_FCLONE_CLONE;
	} else {
		if (skb_pfmemalloc(skb))
			gfp_mask |= __GFP_MEMALLOC;

		n = kmem_cache_alloc(net_hotdata.skbuff_cache, gfp_mask);
		if (!n)
			return NULL;

		n->fclone = SKB_FCLONE_UNAVAILABLE;
	}

	return __skb_clone(n, skb);
}
EXPORT_SYMBOL(skb_clone);

void skb_headers_offset_update(struct sk_buff *skb, int off)
{
	/* Only adjust this if it actually is csum_start rather than csum */
	if (skb->ip_summed == CHECKSUM_PARTIAL)
		skb->csum_start += off;
	/* {transport,network,mac}_header and tail are relative to skb->head */
	skb->transport_header += off;
	skb->network_header   += off;
	if (skb_mac_header_was_set(skb))
		skb->mac_header += off;
	skb->inner_transport_header += off;
	skb->inner_network_header += off;
	skb->inner_mac_header += off;
}
EXPORT_SYMBOL(skb_headers_offset_update);

void skb_copy_header(struct sk_buff *new, const struct sk_buff *old)
{
	__copy_skb_header(new, old);

	skb_shinfo(new)->gso_size = skb_shinfo(old)->gso_size;
	skb_shinfo(new)->gso_segs = skb_shinfo(old)->gso_segs;
	skb_shinfo(new)->gso_type = skb_shinfo(old)->gso_type;
}
EXPORT_SYMBOL(skb_copy_header);

static inline int skb_alloc_rx_flag(const struct sk_buff *skb)
{
	if (skb_pfmemalloc(skb))
		return SKB_ALLOC_RX;
	return 0;
}

/**
 *	skb_copy	-	create private copy of an sk_buff
 *	@skb: buffer to copy
 *	@gfp_mask: allocation priority
 *
 *	Make a copy of both an &sk_buff and its data. This is used when the
 *	caller wishes to modify the data and needs a private copy of the
 *	data to alter. Returns %NULL on failure or the pointer to the buffer
 *	on success. The returned buffer has a reference count of 1.
 *
 *	As by-product this function converts non-linear &sk_buff to linear
 *	one, so that &sk_buff becomes completely private and caller is allowed
 *	to modify all the data of returned buffer. This means that this
 *	function is not recommended for use in circumstances when only
 *	header is going to be modified. Use pskb_copy() instead.
 */

struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
{
	struct sk_buff *n;
	unsigned int size;
	int headerlen;

	if (WARN_ON_ONCE(skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST))
		return NULL;

	headerlen = skb_headroom(skb);
	size = skb_end_offset(skb) + skb->data_len;
	n = __alloc_skb(size, gfp_mask,
			skb_alloc_rx_flag(skb), NUMA_NO_NODE);
	if (!n)
		return NULL;

	/* Set the data pointer */
	skb_reserve(n, headerlen);
	/* Set the tail pointer and length */
	skb_put(n, skb->len);

	BUG_ON(skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len));

	skb_copy_header(n, skb);
	return n;
}
EXPORT_SYMBOL(skb_copy);

/**
 *	__pskb_copy_fclone	-  create copy of an sk_buff with private head.
 *	@skb: buffer to copy
 *	@headroom: headroom of new skb
 *	@gfp_mask: allocation priority
 *	@fclone: if true allocate the copy of the skb from the fclone
 *	cache instead of the head cache; it is recommended to set this
 *	to true for the cases where the copy will likely be cloned
 *
 *	Make a copy of both an &sk_buff and part of its data, located
 *	in header. Fragmented data remain shared. This is used when
 *	the caller wishes to modify only header of &sk_buff and needs
 *	private copy of the header to alter. Returns %NULL on failure
 *	or the pointer to the buffer on success.
 *	The returned buffer has a reference count of 1.
 */

struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
				   gfp_t gfp_mask, bool fclone)
{
	unsigned int size = skb_headlen(skb) + headroom;
	int flags = skb_alloc_rx_flag(skb) | (fclone ? SKB_ALLOC_FCLONE : 0);
	struct sk_buff *n = __alloc_skb(size, gfp_mask, flags, NUMA_NO_NODE);

	if (!n)
		goto out;

	/* Set the data pointer */
	skb_reserve(n, headroom);
	/* Set the tail pointer and length */
	skb_put(n, skb_headlen(skb));
	/* Copy the bytes */
	skb_copy_from_linear_data(skb, n->data, n->len);

	n->truesize += skb->data_len;
	n->data_len  = skb->data_len;
	n->len	     = skb->len;

	if (skb_shinfo(skb)->nr_frags) {
		int i;

		if (skb_orphan_frags(skb, gfp_mask) ||
		    skb_zerocopy_clone(n, skb, gfp_mask)) {
			kfree_skb(n);
			n = NULL;
			goto out;
		}
		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
			skb_shinfo(n)->frags[i] = skb_shinfo(skb)->frags[i];
			skb_frag_ref(skb, i);
		}
		skb_shinfo(n)->nr_frags = i;
	}

	if (skb_has_frag_list(skb)) {
		skb_shinfo(n)->frag_list = skb_shinfo(skb)->frag_list;
		skb_clone_fraglist(n);
	}

	skb_copy_header(n, skb);
out:
	return n;
}
EXPORT_SYMBOL(__pskb_copy_fclone);

/**
 *	pskb_expand_head - reallocate header of &sk_buff
 *	@skb: buffer to reallocate
 *	@nhead: room to add at head
 *	@ntail: room to add at tail
 *	@gfp_mask: allocation priority
 *
 *	Expands (or creates identical copy, if @nhead and @ntail are zero)
 *	header of @skb. &sk_buff itself is not changed. &sk_buff MUST have
 *	reference count of 1. Returns zero in the case of success or error,
 *	if expansion failed. In the last case, &sk_buff is not changed.
 *
 *	All the pointers pointing into skb header may change and must be
 *	reloaded after call to this function.
 */

int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
		     gfp_t gfp_mask)
{
	unsigned int osize = skb_end_offset(skb);
	unsigned int size = osize + nhead + ntail;
	long off;
	u8 *data;
	int i;

	BUG_ON(nhead < 0);

	BUG_ON(skb_shared(skb));

	skb_zcopy_downgrade_managed(skb);

	if (skb_pfmemalloc(skb))
		gfp_mask |= __GFP_MEMALLOC;

	data = kmalloc_reserve(&size, gfp_mask, NUMA_NO_NODE, NULL);
	if (!data)
		goto nodata;
	size = SKB_WITH_OVERHEAD(size);

	/* Copy only real data... and, alas, header. This should be
	 * optimized for the cases when header is void.
	 */
	memcpy(data + nhead, skb->head, skb_tail_pointer(skb) - skb->head);

	memcpy((struct skb_shared_info *)(data + size),
	       skb_shinfo(skb),
	       offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));

	/*
	 * if shinfo is shared we must drop the old head gracefully, but if it
	 * is not we can just drop the old head and let the existing refcount
	 * be since all we did is relocate the values
	 */
	if (skb_cloned(skb)) {
		if (skb_orphan_frags(skb, gfp_mask))
			goto nofrags;
		if (skb_zcopy(skb))
			refcount_inc(&skb_uarg(skb)->refcnt);
		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
			skb_frag_ref(skb, i);

		if (skb_has_frag_list(skb))
			skb_clone_fraglist(skb);

		skb_release_data(skb, SKB_CONSUMED);
	} else {
		skb_free_head(skb);
	}
	off = (data + nhead) - skb->head;

	skb->head     = data;
	skb->head_frag = 0;
	skb->data    += off;

	skb_set_end_offset(skb, size);
#ifdef NET_SKBUFF_DATA_USES_OFFSET
	off           = nhead;
#endif
	skb->tail	      += off;
	skb_headers_offset_update(skb, nhead);
	skb->cloned   = 0;
	skb->hdr_len  = 0;
	skb->nohdr    = 0;
	atomic_set(&skb_shinfo(skb)->dataref, 1);

	skb_metadata_clear(skb);

	/* It is not generally safe to change skb->truesize.
	 * For the moment, we really care of rx path, or
	 * when skb is orphaned (not attached to a socket).
	 */
	if (!skb->sk || skb->destructor == sock_edemux)
		skb->truesize += size - osize;

	return 0;

nofrags:
	skb_kfree_head(data, size);
nodata:
	return -ENOMEM;
}
EXPORT_SYMBOL(pskb_expand_head);

/* Make private copy of skb with writable head and some headroom */

struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)
{
	struct sk_buff *skb2;
	int delta = headroom - skb_headroom(skb);

	if (delta <= 0)
		skb2 = pskb_copy(skb, GFP_ATOMIC);
	else {
		skb2 = skb_clone(skb, GFP_ATOMIC);
		if (skb2 && pskb_expand_head(skb2, SKB_DATA_ALIGN(delta), 0,
					     GFP_ATOMIC)) {
			kfree_skb(skb2);
			skb2 = NULL;
		}
	}
	return skb2;
}
EXPORT_SYMBOL(skb_realloc_headroom);

/* Note: We plan to rework this in linux-6.4 */
int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri)
{
	unsigned int saved_end_offset, saved_truesize;
	struct skb_shared_info *shinfo;
	int res;

	saved_end_offset = skb_end_offset(skb);
	saved_truesize = skb->truesize;

	res = pskb_expand_head(skb, 0, 0, pri);
	if (res)
		return res;

	skb->truesize = saved_truesize;

	if (likely(skb_end_offset(skb) == saved_end_offset))
		return 0;

	/* We can not change skb->end if the original or new value
	 * is SKB_SMALL_HEAD_HEADROOM, as it might break skb_kfree_head().
	 */
	if (saved_end_offset == SKB_SMALL_HEAD_HEADROOM ||
	    skb_end_offset(skb) == SKB_SMALL_HEAD_HEADROOM) {
		/* We think this path should not be taken.
		 * Add a temporary trace to warn us just in case.
		 */
		pr_err_once("__skb_unclone_keeptruesize() skb_end_offset() %u -> %u\n",
			    saved_end_offset, skb_end_offset(skb));
		WARN_ON_ONCE(1);
		return 0;
	}

	shinfo = skb_shinfo(skb);

	/* We are about to change back skb->end,
	 * we need to move skb_shinfo() to its new location.
	 */
	memmove(skb->head + saved_end_offset,
		shinfo,
		offsetof(struct skb_shared_info, frags[shinfo->nr_frags]));

	skb_set_end_offset(skb, saved_end_offset);

	return 0;
}

/**
 *	skb_expand_head - reallocate header of &sk_buff
 *	@skb: buffer to reallocate
 *	@headroom: needed headroom
 *
 *	Unlike skb_realloc_headroom, this one does not allocate a new skb
 *	if possible; copies skb->sk to new skb as needed
 *	and frees original skb in case of failures.
 *
 *	It expect increased headroom and generates warning otherwise.
 */

struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
{
	int delta = headroom - skb_headroom(skb);
	int osize = skb_end_offset(skb);
	struct sock *sk = skb->sk;

	if (WARN_ONCE(delta <= 0,
		      "%s is expecting an increase in the headroom", __func__))
		return skb;

	delta = SKB_DATA_ALIGN(delta);
	/* pskb_expand_head() might crash, if skb is shared. */
	if (skb_shared(skb) || !is_skb_wmem(skb)) {
		struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);

		if (unlikely(!nskb))
			goto fail;

		if (sk)
			skb_set_owner_w(nskb, sk);
		consume_skb(skb);
		skb = nskb;
	}
	if (pskb_expand_head(skb, delta, 0, GFP_ATOMIC))
		goto fail;

	if (sk && is_skb_wmem(skb)) {
		delta = skb_end_offset(skb) - osize;
		refcount_add(delta, &sk->sk_wmem_alloc);
		skb->truesize += delta;
	}
	return skb;

fail:
	kfree_skb(skb);
	return NULL;
}
EXPORT_SYMBOL(skb_expand_head);

/**
 *	skb_copy_expand	-	copy and expand sk_buff
 *	@skb: buffer to copy
 *	@newheadroom: new free bytes at head
 *	@newtailroom: new free bytes at tail
 *	@gfp_mask: allocation priority
 *
 *	Make a copy of both an &sk_buff and its data and while doing so
 *	allocate additional space.
 *
 *	This is used when the caller wishes to modify the data and needs a
 *	private copy of the data to alter as well as more space for new fields.
 *	Returns %NULL on failure or the pointer to the buffer
 *	on success. The returned buffer has a reference count of 1.
 *
 *	You must pass %GFP_ATOMIC as the allocation priority if this function
 *	is called from an interrupt.
 */
struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
				int newheadroom, int newtailroom,
				gfp_t gfp_mask)
{
	/*
	 *	Allocate the copy buffer
	 */
	int head_copy_len, head_copy_off;
	struct sk_buff *n;
	int oldheadroom;

	if (WARN_ON_ONCE(skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST))
		return NULL;

	oldheadroom = skb_headroom(skb);
	n = __alloc_skb(newheadroom + skb->len + newtailroom,
			gfp_mask, skb_alloc_rx_flag(skb),
			NUMA_NO_NODE);
	if (!n)
		return NULL;

	skb_reserve(n, newheadroom);

	/* Set the tail pointer and length */
	skb_put(n, skb->len);

	head_copy_len = oldheadroom;
	head_copy_off = 0;
	if (newheadroom <= head_copy_len)
		head_copy_len = newheadroom;
	else
		head_copy_off = newheadroom - head_copy_len;

	/* Copy the linear header and data. */
	BUG_ON(skb_copy_bits(skb, -head_copy_len, n->head + head_copy_off,
			     skb->len + head_copy_len));

	skb_copy_header(n, skb);

	skb_headers_offset_update(n, newheadroom - oldheadroom);

	return n;
}
EXPORT_SYMBOL(skb_copy_expand);

/**
 *	__skb_pad		-	zero pad the tail of an skb
 *	@skb: buffer to pad
 *	@pad: space to pad
 *	@free_on_error: free buffer on error
 *
 *	Ensure that a buffer is followed by a padding area that is zero
 *	filled. Used by network drivers which may DMA or transfer data
 *	beyond the buffer end onto the wire.
 *
 *	May return error in out of memory cases. The skb is freed on error
 *	if @free_on_error is true.
 */

int __skb_pad(struct sk_buff *skb, int pad, bool free_on_error)
{
	int err;
	int ntail;

	/* If the skbuff is non linear tailroom is always zero.. */
	if (!skb_cloned(skb) && skb_tailroom(skb) >= pad) {
		memset(skb->data+skb->len, 0, pad);
		return 0;
	}

	ntail = skb->data_len + pad - (skb->end - skb->tail);
	if (likely(skb_cloned(skb) || ntail > 0)) {
		err = pskb_expand_head(skb, 0, ntail, GFP_ATOMIC);
		if (unlikely(err))
			goto free_skb;
	}

	/* FIXME: The use of this function with non-linear skb's really needs
	 * to be audited.
	 */
	err = skb_linearize(skb);
	if (unlikely(err))
		goto free_skb;

	memset(skb->data + skb->len, 0, pad);
	return 0;

free_skb:
	if (free_on_error)
		kfree_skb(skb);
	return err;
}
EXPORT_SYMBOL(__skb_pad);

/**
 *	pskb_put - add data to the tail of a potentially fragmented buffer
 *	@skb: start of the buffer to use
 *	@tail: tail fragment of the buffer to use
 *	@len: amount of data to add
 *
 *	This function extends the used data area of the potentially
 *	fragmented buffer. @tail must be the last fragment of @skb -- or
 *	@skb itself. If this would exceed the total buffer size the kernel
 *	will panic. A pointer to the first byte of the extra data is
 *	returned.
 */

void *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len)
{
	if (tail != skb) {
		skb->data_len += len;
		skb->len += len;
	}
	return skb_put(tail, len);
}
EXPORT_SYMBOL_GPL(pskb_put);

/**
 *	skb_put - add data to a buffer
 *	@skb: buffer to use
 *	@len: amount of data to add
 *
 *	This function extends the used data area of the buffer. If this would
 *	exceed the total buffer size the kernel will panic. A pointer to the
 *	first byte of the extra data is returned.
 */
void *skb_put(struct sk_buff *skb, unsigned int len)
{
	void *tmp = skb_tail_pointer(skb);
	SKB_LINEAR_ASSERT(skb);
	skb->tail += len;
	skb->len  += len;
	if (unlikely(skb->tail > skb->end))
		skb_over_panic(skb, len, __builtin_return_address(0));
	return tmp;
}
EXPORT_SYMBOL(skb_put);

/**
 *	skb_push - add data to the start of a buffer
 *	@skb: buffer to use
 *	@len: amount of data to add
 *
 *	This function extends the used data area of the buffer at the buffer
 *	start. If this would exceed the total buffer headroom the kernel will
 *	panic. A pointer to the first byte of the extra data is returned.
 */
void *skb_push(struct sk_buff *skb, unsigned int len)
{
	skb->data -= len;
	skb->len  += len;
	if (unlikely(skb->data < skb->head))
		skb_under_panic(skb, len, __builtin_return_address(0));
	return skb->data;
}
EXPORT_SYMBOL(skb_push);

/**
 *	skb_pull - remove data from the start of a buffer
 *	@skb: buffer to use
 *	@len: amount of data to remove
 *
 *	This function removes data from the start of a buffer, returning
 *	the memory to the headroom. A pointer to the next data in the buffer
 *	is returned. Once the data has been pulled future pushes will overwrite
 *	the old data.
 */
void *skb_pull(struct sk_buff *skb, unsigned int len)
{
	return skb_pull_inline(skb, len);
}
EXPORT_SYMBOL(skb_pull);

/**
 *	skb_pull_data - remove data from the start of a buffer returning its
 *	original position.
 *	@skb: buffer to use
 *	@len: amount of data to remove
 *
 *	This function removes data from the start of a buffer, returning
 *	the memory to the headroom. A pointer to the original data in the buffer
 *	is returned after checking if there is enough data to pull. Once the
 *	data has been pulled future pushes will overwrite the old data.
 */
void *skb_pull_data(struct sk_buff *skb, size_t len)
{
	void *data = skb->data;

	if (skb->len < len)
		return NULL;

	skb_pull(skb, len);

	return data;
}
EXPORT_SYMBOL(skb_pull_data);

/**
 *	skb_trim - remove end from a buffer
 *	@skb: buffer to alter
 *	@len: new length
 *
 *	Cut the length of a buffer down by removing data from the tail. If
 *	the buffer is already under the length specified it is not modified.
 *	The skb must be linear.
 */
void skb_trim(struct sk_buff *skb, unsigned int len)
{
	if (skb->len > len)
		__skb_trim(skb, len);
}
EXPORT_SYMBOL(skb_trim);

/* Trims skb to length len. It can change skb pointers.
 */

int ___pskb_trim(struct sk_buff *skb, unsigned int len)
{
	struct sk_buff **fragp;
	struct sk_buff *frag;
	int offset = skb_headlen(skb);
	int nfrags = skb_shinfo(skb)->nr_frags;
	int i;
	int err;

	if (skb_cloned(skb) &&
	    unlikely((err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC))))
		return err;

	i = 0;
	if (offset >= len)
		goto drop_pages;

	for (; i < nfrags; i++) {
		int end = offset + skb_frag_size(&skb_shinfo(skb)->frags[i]);

		if (end < len) {
			offset = end;
			continue;
		}

		skb_frag_size_set(&skb_shinfo(skb)->frags[i++], len - offset);

drop_pages:
		skb_shinfo(skb)->nr_frags = i;

		for (; i < nfrags; i++)
			skb_frag_unref(skb, i);

		if (skb_has_frag_list(skb))
			skb_drop_fraglist(skb);
		goto done;
	}

	for (fragp = &skb_shinfo(skb)->frag_list; (frag = *fragp);
	     fragp = &frag->next) {
		int end = offset + frag->len;

		if (skb_shared(frag)) {
			struct sk_buff *nfrag;

			nfrag = skb_clone(frag, GFP_ATOMIC);
			if (unlikely(!nfrag))
				return -ENOMEM;

			nfrag->next = frag->next;
			consume_skb(frag);
			frag = nfrag;
			*fragp = frag;
		}

		if (end < len) {
			offset = end;
			continue;
		}

		if (end > len &&
		    unlikely((err = pskb_trim(frag, len - offset))))
			return err;

		if (frag->next)
			skb_drop_list(&frag->next);
		break;
	}

done:
	if (len > skb_headlen(skb)) {
		skb->data_len -= skb->len - len;
		skb->len       = len;
	} else {
		skb->len       = len;
		skb->data_len  = 0;
		skb_set_tail_pointer(skb, len);
	}

	if (!skb->sk || skb->destructor == sock_edemux)
		skb_condense(skb);
	return 0;
}
EXPORT_SYMBOL(___pskb_trim);

/* Note : use pskb_trim_rcsum() instead of calling this directly
 */
int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len)
{
	if (skb->ip_summed == CHECKSUM_COMPLETE) {
		int delta = skb->len - len;

		skb->csum = csum_block_sub(skb->csum,
					   skb_checksum(skb, len, delta, 0),
					   len);
	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
		int hdlen = (len > skb_headlen(skb)) ? skb_headlen(skb) : len;
		int offset = skb_checksum_start_offset(skb) + skb->csum_offset;

		if (offset + sizeof(__sum16) > hdlen)
			return -EINVAL;
	}
	return __pskb_trim(skb, len);
}
EXPORT_SYMBOL(pskb_trim_rcsum_slow);

/**
 *	__pskb_pull_tail - advance tail of skb header
 *	@skb: buffer to reallocate
 *	@delta: number of bytes to advance tail
 *
 *	The function makes a sense only on a fragmented &sk_buff,
 *	it expands header moving its tail forward and copying necessary
 *	data from fragmented part.
 *
 *	&sk_buff MUST have reference count of 1.
 *
 *	Returns %NULL (and &sk_buff does not change) if pull failed
 *	or value of new tail of skb in the case of success.
 *
 *	All the pointers pointing into skb header may change and must be
 *	reloaded after call to this function.
 */

/* Moves tail of skb head forward, copying data from fragmented part,
 * when it is necessary.
 * 1. It may fail due to malloc failure.
 * 2. It may change skb pointers.
 *
 * It is pretty complicated. Luckily, it is called only in exceptional cases.
 */
void *__pskb_pull_tail(struct sk_buff *skb, int delta)
{
	/* If skb has not enough free space at tail, get new one
	 * plus 128 bytes for future expansions. If we have enough
	 * room at tail, reallocate without expansion only if skb is cloned.
	 */
	int i, k, eat = (skb->tail + delta) - skb->end;

	if (eat > 0 || skb_cloned(skb)) {
		if (pskb_expand_head(skb, 0, eat > 0 ? eat + 128 : 0,
				     GFP_ATOMIC))
			return NULL;
	}

	BUG_ON(skb_copy_bits(skb, skb_headlen(skb),
			     skb_tail_pointer(skb), delta));

	/* Optimization: no fragments, no reasons to preestimate
	 * size of pulled pages. Superb.
	 */
	if (!skb_has_frag_list(skb))
		goto pull_pages;

	/* Estimate size of pulled pages. */
	eat = delta;
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
		int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);

		if (size >= eat)
			goto pull_pages;
		eat -= size;
	}

	/* If we need update frag list, we are in troubles.
	 * Certainly, it is possible to add an offset to skb data,
	 * but taking into account that pulling is expected to
	 * be very rare operation, it is worth to fight against
	 * further bloating skb head and crucify ourselves here instead.
	 * Pure masohism, indeed. 8)8)
	 */
	if (eat) {
		struct sk_buff *list = skb_shinfo(skb)->frag_list;
		struct sk_buff *clone = NULL;
		struct sk_buff *insp = NULL;

		do {
			if (list->len <= eat) {
				/* Eaten as whole. */
				eat -= list->len;
				list = list->next;
				insp = list;
			} else {
				/* Eaten partially. */
				if (skb_is_gso(skb) && !list->head_frag &&
				    skb_headlen(list))
					skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;

				if (skb_shared(list)) {
					/* Sucks! We need to fork list. :-( */
					clone = skb_clone(list, GFP_ATOMIC);
					if (!clone)
						return NULL;
					insp = list->next;
					list = clone;
				} else {
					/* This may be pulled without
					 * problems. */
					insp = list;
				}
				if (!pskb_pull(list, eat)) {
					kfree_skb(clone);
					return NULL;
				}
				break;
			}
		} while (eat);

		/* Free pulled out fragments. */
		while ((list = skb_shinfo(skb)->frag_list) != insp) {
			skb_shinfo(skb)->frag_list = list->next;
			consume_skb(list);
		}
		/* And insert new clone at head. */
		if (clone) {
			clone->next = list;
			skb_shinfo(skb)->frag_list = clone;
		}
	}
	/* Success! Now we may commit changes to skb data. */

pull_pages:
	eat = delta;
	k = 0;
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
		int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);

		if (size <= eat) {
			skb_frag_unref(skb, i);
			eat -= size;
		} else {
			skb_frag_t *frag = &skb_shinfo(skb)->frags[k];

			*frag = skb_shinfo(skb)->frags[i];
			if (eat) {
				skb_frag_off_add(frag, eat);
				skb_frag_size_sub(frag, eat);
				if (!i)
					goto end;
				eat = 0;
			}
			k++;
		}
	}
	skb_shinfo(skb)->nr_frags = k;

end:
	skb->tail     += delta;
	skb->data_len -= delta;

	if (!skb->data_len)
		skb_zcopy_clear(skb, false);

	return skb_tail_pointer(skb);
}
EXPORT_SYMBOL(__pskb_pull_tail);

/**
 *	skb_copy_bits - copy bits from skb to kernel buffer
 *	@skb: source skb
 *	@offset: offset in source
 *	@to: destination buffer
 *	@len: number of bytes to copy
 *
 *	Copy the specified number of bytes from the source skb to the
 *	destination buffer.
 *
 *	CAUTION ! :
 *		If its prototype is ever changed,
 *		check arch/{*}/net/{*}.S files,
 *		since it is called from BPF assembly code.
 */
int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
{
	int start = skb_headlen(skb);
	struct sk_buff *frag_iter;
	int i, copy;

	if (offset > (int)skb->len - len)
		goto fault;

	/* Copy header. */
	if ((copy = start - offset) > 0) {
		if (copy > len)
			copy = len;
		skb_copy_from_linear_data_offset(skb, offset, to, copy);
		if ((len -= copy) == 0)
			return 0;
		offset += copy;
		to     += copy;
	}

	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
		int end;
		skb_frag_t *f = &skb_shinfo(skb)->frags[i];

		WARN_ON(start > offset + len);

		end = start + skb_frag_size(f);
		if ((copy = end - offset) > 0) {
			u32 p_off, p_len, copied;
			struct page *p;
			u8 *vaddr;

			if (copy > len)
				copy = len;

			skb_frag_foreach_page(f,
					      skb_frag_off(f) + offset - start,
					      copy, p, p_off, p_len, copied) {
				vaddr = kmap_atomic(p);
				memcpy(to + copied, vaddr + p_off, p_len);
				kunmap_atomic(vaddr);
			}

			if ((len -= copy) == 0)
				return 0;
			offset += copy;
			to     += copy;
		}
		start = end;
	}

	skb_walk_frags(skb, frag_iter) {
		int end;

		WARN_ON(start > offset + len);

		end = start + frag_iter->len;
		if ((copy = end - offset) > 0) {
			if (copy > len)
				copy = len;
			if (skb_copy_bits(frag_iter, offset - start, to, copy))
				goto fault;
			if ((len -= copy) == 0)
				return 0;
			offset += copy;
			to     += copy;
		}
		start = end;
	}

	if (!len)
		return 0;

fault:
	return -EFAULT;
}
EXPORT_SYMBOL(skb_copy_bits);

/*
 * Callback from splice_to_pipe(), if we need to release some pages
 * at the end of the spd in case we error'ed out in filling the pipe.
 */
static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
{
	put_page(spd->pages[i]);
}

static struct page *linear_to_page(struct page *page, unsigned int *len,
				   unsigned int *offset,
				   struct sock *sk)
{
	struct page_frag *pfrag = sk_page_frag(sk);

	if (!sk_page_frag_refill(sk, pfrag))
		return NULL;

	*len = min_t(unsigned int, *len, pfrag->size - pfrag->offset);

	memcpy(page_address(pfrag->page) + pfrag->offset,
	       page_address(page) + *offset, *len);
	*offset = pfrag->offset;
	pfrag->offset += *len;

	return pfrag->page;
}

static bool spd_can_coalesce(const struct splice_pipe_desc *spd,
			     struct page *page,
			     unsigned int offset)
{
	return	spd->nr_pages &&
		spd->pages[spd->nr_pages - 1] == page &&
		(spd->partial[spd->nr_pages - 1].offset +
		 spd->partial[spd->nr_pages - 1].len == offset);
}

/*
 * Fill page/offset/length into spd, if it can hold more pages.
 */
static bool spd_fill_page(struct splice_pipe_desc *spd,
			  struct pipe_inode_info *pipe, struct page *page,
			  unsigned int *len, unsigned int offset,
			  bool linear,
			  struct sock *sk)
{
	if (unlikely(spd->nr_pages == MAX_SKB_FRAGS))
		return true;

	if (linear) {
		page = linear_to_page(page, len, &offset, sk);
		if (!page)
			return true;
	}
	if (spd_can_coalesce(spd, page, offset)) {
		spd->partial[spd->nr_pages - 1].len += *len;
		return false;
	}
	get_page(page);
	spd->pages[spd->nr_pages] = page;
	spd->partial[spd->nr_pages].len = *len;
	spd->partial[spd->nr_pages].offset = offset;
	spd->nr_pages++;

	return false;
}

static bool __splice_segment(struct page *page, unsigned int poff,
			     unsigned int plen, unsigned int *off,
			     unsigned int *len,
			     struct splice_pipe_desc *spd, bool linear,
			     struct sock *sk,
			     struct pipe_inode_info *pipe)
{
	if (!*len)
		return true;

	/* skip this segment if already processed */
	if (*off >= plen) {
		*off -= plen;
		return false;
	}

	/* ignore any bits we already processed */
	poff += *off;
	plen -= *off;
	*off = 0;

	do {
		unsigned int flen = min(*len, plen);

		if (spd_fill_page(spd, pipe, page, &flen, poff,
				  linear, sk))
			return true;
		poff += flen;
		plen -= flen;
		*len -= flen;
	} while (*len && plen);

	return false;
}

/*
 * Map linear and fragment data from the skb to spd. It reports true if the
 * pipe is full or if we already spliced the requested length.
 */
static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
			      unsigned int *offset, unsigned int *len,
			      struct splice_pipe_desc *spd, struct sock *sk)
{
	int seg;
	struct sk_buff *iter;

	/* map the linear part :
	 * If skb->head_frag is set, this 'linear' part is backed by a
	 * fragment, and if the head is not shared with any clones then
	 * we can avoid a copy since we own the head portion of this page.
	 */
	if (__splice_segment(virt_to_page(skb->data),
			     (unsigned long) skb->data & (PAGE_SIZE - 1),
			     skb_headlen(skb),
			     offset, len, spd,
			     skb_head_is_locked(skb),
			     sk, pipe))
		return true;

	/*
	 * then map the fragments
	 */
	for (seg = 0; seg < skb_shinfo(skb)->nr_frags; seg++) {
		const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];

		if (__splice_segment(skb_frag_page(f),
				     skb_frag_off(f), skb_frag_size(f),
				     offset, len, spd, false, sk, pipe))
			return true;
	}

	skb_walk_frags(skb, iter) {
		if (*offset >= iter->len) {
			*offset -= iter->len;
			continue;
		}
		/* __skb_splice_bits() only fails if the output has no room
		 * left, so no point in going over the frag_list for the error
		 * case.
		 */
		if (__skb_splice_bits(iter, pipe, offset, len, spd, sk))
			return true;
	}

	return false;
}

/*
 * Map data from the skb to a pipe. Should handle both the linear part,
 * the fragments, and the frag list.
 */
int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
		    struct pipe_inode_info *pipe, unsigned int tlen,
		    unsigned int flags)
{
	struct partial_page partial[MAX_SKB_FRAGS];
	struct page *pages[MAX_SKB_FRAGS];
	struct splice_pipe_desc spd = {
		.pages = pages,
		.partial = partial,
		.nr_pages_max = MAX_SKB_FRAGS,
		.ops = &nosteal_pipe_buf_ops,
		.spd_release = sock_spd_release,
	};
	int ret = 0;

	__skb_splice_bits(skb, pipe, &offset, &tlen, &spd, sk);

	if (spd.nr_pages)
		ret = splice_to_pipe(pipe, &spd);

	return ret;
}
EXPORT_SYMBOL_GPL</