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Thu, 08 Oct 2026 14:03:18 -0700 (PDT) From: Josef Bacik Date: Thu, 08 Oct 2026 21:02:48 +0000 Subject: [PATCH net-next v2 01/10] net: skbuff: add skb_drop_empty_frags() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261008-b4-pskb-pull-tail-drivers-v2-1-8f2bd9bee138@toxicpanda.com> References: <20261008-b4-pskb-pull-tail-drivers-v2-0-8f2bd9bee138@toxicpanda.com> In-Reply-To: <20261008-b4-pskb-pull-tail-drivers-v2-0-8f2bd9bee138@toxicpanda.com> To: Jakub Kicinski , Paolo Abeni , Eric Dumazet , "David S. Miller" , Andrew Lunn Cc: Saeed Mahameed , Tariq Toukan , Mark Bloch , Leon Romanovsky , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Tony Nguyen , Przemek Kitszel , Manish Chopra , Rahul Verma , GR-Linux-NIC-Dev@marvell.com, Shahed Shaikh , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, xen-devel@lists.xenproject.org, intel-wired-lan@lists.osuosl.org, Josef Bacik X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openssh-sha256; t=1791493384; l=3047; i=josef@toxicpanda.com; h=from:subject:message-id; bh=eNF9AfY31ifKJcp/wEnDWb5NxkFPFrVkSamyLYsUttM=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgUBr36M/n0nWN0DNbnxwzIiCZez6MG JiruuNaSCI/zXsAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QOI8lG/wdh6wd8yc4i7FHBwvmuyCaLtAuFDjmIGDKRvpDQpmhSkJsjkYyP5E/1+czZMvAKz61ka mmydLfI/gLQo= X-Developer-Key: i=josef@toxicpanda.com; a=openssh; fpr=SHA256:C8kOX2QUJCMqnCX+KEeoqRAjLo9L+ELOSH2NSAJHqGA __pskb_pull_tail() releases every zero-length page frag as it walks the frags array, even when it's asked to pull nothing. Some drivers depend on that. xen-netfront calls it with a zero count on purpose to make room when a backend fills the frags with empty slots, see commit d81c5054a5d1 ("xen/netfront: tolerate frags with no data"). netxen and qlcnic get the same effect when the frags they pull to fit a TX descriptor happen to be empty. pskb_may_pull() returns before getting there when the head already holds the requested length, so these drivers can't simply switch to it. Add skb_drop_empty_frags() to do just that part, unsharing the skb first if it's cloned like __pskb_pull_tail() does. Assisted-by: LLM Signed-off-by: Josef Bacik --- include/linux/skbuff.h | 1 + net/core/skbuff.c | 40 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 27ec1e38c828..c1295f6baf6d 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2840,6 +2840,7 @@ static inline void *skb_pull_inline(struct sk_buff *skb, unsigned int len) void *skb_pull_data(struct sk_buff *skb, size_t len); void *__pskb_pull_tail(struct sk_buff *skb, int delta); +int skb_drop_empty_frags(struct sk_buff *skb, gfp_t gfp); static __always_inline enum skb_drop_reason pskb_may_pull_reason(struct sk_buff *skb, unsigned int len) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 43ebe61c7fc4..f798118df112 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3004,6 +3004,46 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta) } EXPORT_SYMBOL(__pskb_pull_tail); +/** + * skb_drop_empty_frags - release the zero-length page frags of an skb + * @skb: buffer to clean up + * @gfp: allocation priority, used if @skb has to be unshared + * + * Releases every page frag of @skb that holds no data and closes up + * the frags array, so the remaining frags keep their order. The + * frag_list is left alone. A cloned @skb is unshared first, since + * the frags array is shared between clones. + * + * Returns 0 on success, or -ENOMEM if @skb had to be unshared and + * that failed, in which case @skb is unchanged. + */ +int skb_drop_empty_frags(struct sk_buff *skb, gfp_t gfp) +{ + struct skb_shared_info *shinfo = skb_shinfo(skb); + int i, k; + + for (i = 0; i < shinfo->nr_frags; i++) + if (!skb_frag_size(&shinfo->frags[i])) + break; + if (i == shinfo->nr_frags) + return 0; + + if (skb_unclone(skb, gfp)) + return -ENOMEM; + + shinfo = skb_shinfo(skb); + for (i = 0, k = 0; i < shinfo->nr_frags; i++) { + if (!skb_frag_size(&shinfo->frags[i])) { + skb_frag_unref(skb, i); + continue; + } + shinfo->frags[k++] = shinfo->frags[i]; + } + shinfo->nr_frags = k; + return 0; +} +EXPORT_SYMBOL(skb_drop_empty_frags); + /** * skb_copy_bits - copy bits from skb to kernel buffer * @skb: source skb -- 2.55.0