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skbuff: introduce skb_expand_head()

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[ Upstream commit f1260ff15a71b8fc122b2c9abd8a7abffb6e0168 ]

Like skb_realloc_headroom(), new helper increases headroom of specified skb.
Unlike skb_realloc_headroom(), it does not allocate a new skb if possible;
copies skb->sk on new skb when as needed and frees original skb in case
of failures.

This helps to simplify ip[6]_finish_output2() and a few other similar cases.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit f1260ff15a71b8fc122b2c9abd8a7abffb6e0168)
Signed-off-by: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Vasily Averin 2024-12-24 21:16:21 -08:00 • committed by Ksawlii
parent 61e1810272
commit a8a822bd1e
2 changed files with 43 additions and 0 deletions
include/linux
skbuff.h
net/core
skbuff.c

1
include/linux/skbuff.h
View file

@ -1196,6 +1196,7 @@ static inline struct sk_buff *__pskb_copy(struct sk_buff *skb, int headroom,
int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, gfp_t gfp_mask);
struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
unsigned int headroom);
struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom);
struct sk_buff *skb_copy_expand(const struct sk_buff *skb, int newheadroom,
int newtailroom, gfp_t priority);
int __must_check skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,

42
net/core/skbuff.c
View file

@ -1765,6 +1765,48 @@ int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri)
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);
if (WARN_ONCE(delta <= 0,
"%s is expecting an increase in the headroom", __func__))
return skb;
/* pskb_expand_head() might crash, if skb is shared */
if (skb_shared(skb)) {
struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
if (likely(nskb)) {
if (skb->sk)
skb_set_owner_w(nskb, skb->sk);
consume_skb(skb);
} else {
kfree_skb(skb);
}
skb = nskb;
}
if (skb &&
pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
kfree_skb(skb);
skb = NULL;
}
return skb;
}
EXPORT_SYMBOL(skb_expand_head);
/**
* skb_copy_expand - copy and expand sk_buff
* @skb: buffer to copy