On 05/01, Jon Kohler wrote: > > > > On Apr 30, 2025, at 5:09 PM, Stanislav Fomichev <stfomichev@xxxxxxxxx> wrote: > > > > !-------------------------------------------------------------------| > > CAUTION: External Email > > > > |-------------------------------------------------------------------! > > > > On 04/30, Jon Kohler wrote: > >> Introduce new XDP helpers: > >> - xdp_headlen: Similar to skb_headlen > >> - xdp_headroom: Similar to skb_headroom > >> - xdp_metadata_len: Similar to skb_metadata_len > >> > >> Integrate these helpers into tap, tun, and XDP implementation to start. > >> > >> No functional changes introduced. > >> > >> Signed-off-by: Jon Kohler <jon@xxxxxxxxxxx> > >> --- > >> v1->v2: Integrate feedback from Willem > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__patchwork.kernel.org_project_netdevbpf_patch_20250430182921.1704021-2D1-2Djon-40nutanix.com_&d=DwIBaQ&c=s883GpUCOChKOHiocYtGcg&r=NGPRGGo37mQiSXgHKm5rCQ&m=9pdxzQszX_M0K3gEPeYOyMZZYSkRR8IMvxslS8320Eoctk58y-ELCdZ5iaryF2GH&s=J-ILB7E9VQ_plo0hyjEtzGzjy6G0_o4MMMmmE_z8vvc&e= > >> > >> drivers/net/tap.c | 6 +++--- > >> drivers/net/tun.c | 12 +++++------ > >> include/net/xdp.h | 54 +++++++++++++++++++++++++++++++++++++++++++---- > >> net/core/xdp.c | 12 +++++------ > >> 4 files changed, 65 insertions(+), 19 deletions(-) > >> > >> diff --git a/drivers/net/tap.c b/drivers/net/tap.c > >> index d4ece538f1b2..a62fbca4b08f 100644 > >> --- a/drivers/net/tap.c > >> +++ b/drivers/net/tap.c > >> @@ -1048,7 +1048,7 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp) > >> struct sk_buff *skb; > >> int err, depth; > >> > >> - if (unlikely(xdp->data_end - xdp->data < ETH_HLEN)) { > >> + if (unlikely(xdp_headlen(xdp) < ETH_HLEN)) { > >> err = -EINVAL; > >> goto err; > >> } > >> @@ -1062,8 +1062,8 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp) > >> goto err; > >> } > >> > >> - skb_reserve(skb, xdp->data - xdp->data_hard_start); > >> - skb_put(skb, xdp->data_end - xdp->data); > >> + skb_reserve(skb, xdp_headroom(xdp)); > >> + skb_put(skb, xdp_headlen(xdp)); > >> > >> skb_set_network_header(skb, ETH_HLEN); > >> skb_reset_mac_header(skb); > >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c > >> index 7babd1e9a378..4c47eed71986 100644 > >> --- a/drivers/net/tun.c > >> +++ b/drivers/net/tun.c > >> @@ -1567,7 +1567,7 @@ static int tun_xdp_act(struct tun_struct *tun, struct bpf_prog *xdp_prog, > >> dev_core_stats_rx_dropped_inc(tun->dev); > >> return err; > >> } > >> - dev_sw_netstats_rx_add(tun->dev, xdp->data_end - xdp->data); > >> + dev_sw_netstats_rx_add(tun->dev, xdp_headlen(xdp)); > >> break; > >> case XDP_TX: > >> err = tun_xdp_tx(tun->dev, xdp); > >> @@ -1575,7 +1575,7 @@ static int tun_xdp_act(struct tun_struct *tun, struct bpf_prog *xdp_prog, > >> dev_core_stats_rx_dropped_inc(tun->dev); > >> return err; > >> } > >> - dev_sw_netstats_rx_add(tun->dev, xdp->data_end - xdp->data); > >> + dev_sw_netstats_rx_add(tun->dev, xdp_headlen(xdp)); > >> break; > >> case XDP_PASS: > >> break; > >> @@ -2355,7 +2355,7 @@ static int tun_xdp_one(struct tun_struct *tun, > >> struct xdp_buff *xdp, int *flush, > >> struct tun_page *tpage) > >> { > >> - unsigned int datasize = xdp->data_end - xdp->data; > >> + unsigned int datasize = xdp_headlen(xdp); > >> struct tun_xdp_hdr *hdr = xdp->data_hard_start; > >> struct virtio_net_hdr *gso = &hdr->gso; > >> struct bpf_prog *xdp_prog; > >> @@ -2415,14 +2415,14 @@ static int tun_xdp_one(struct tun_struct *tun, > >> goto out; > >> } > >> > >> - skb_reserve(skb, xdp->data - xdp->data_hard_start); > >> - skb_put(skb, xdp->data_end - xdp->data); > >> + skb_reserve(skb, xdp_headroom(xdp)); > >> + skb_put(skb, xdp_headlen(xdp)); > >> > >> /* The externally provided xdp_buff may have no metadata support, which > >> * is marked by xdp->data_meta being xdp->data + 1. This will lead to a > >> * metasize of -1 and is the reason why the condition checks for > 0. > >> */ > >> - metasize = xdp->data - xdp->data_meta; > >> + metasize = xdp_metadata_len(xdp); > >> if (metasize > 0) > >> skb_metadata_set(skb, metasize); > >> > >> diff --git a/include/net/xdp.h b/include/net/xdp.h > >> index 48efacbaa35d..044345b18305 100644 > >> --- a/include/net/xdp.h > >> +++ b/include/net/xdp.h > >> @@ -151,10 +151,56 @@ xdp_get_shared_info_from_buff(const struct xdp_buff *xdp) > >> return (struct skb_shared_info *)xdp_data_hard_end(xdp); > >> } > >> > >> +/** > >> + * xdp_headlen - Calculate the length of the data in an XDP buffer > >> + * @xdp: Pointer to the XDP buffer structure > >> + * > >> + * Compute the length of the data contained in the XDP buffer. Does not > >> + * include frags, use xdp_get_buff_len() for that instead. > >> + * > >> + * Analogous to skb_headlen(). > >> + * > >> + * Return: The length of the data in the XDP buffer in bytes. > >> + */ > >> +static inline unsigned int xdp_headlen(const struct xdp_buff *xdp) > >> +{ > >> + return xdp->data_end - xdp->data; > >> +} > >> + > >> +/** > >> + * xdp_headroom - Calculate the headroom available in an XDP buffer > >> + * @xdp: Pointer to the XDP buffer structure > >> + * > >> + * Compute the headroom in an XDP buffer. > >> + * > >> + * Analogous to the skb_headroom(). > >> + * > >> + * Return: The size of the headroom in bytes. > >> + */ > >> +static inline unsigned int xdp_headroom(const struct xdp_buff *xdp) > >> +{ > >> + return xdp->data - xdp->data_hard_start; > >> +} > >> + > >> +/** > >> + * xdp_metadata_len - Calculate the length of metadata in an XDP buffer > >> + * @xdp: Pointer to the XDP buffer structure > >> + * > >> + * Compute the length of the metadata region in an XDP buffer. > >> + * > >> + * Analogous to skb_metadata_len(). > >> + * > >> + * Return: The length of the metadata in bytes. > >> + */ > >> +static inline unsigned int xdp_metadata_len(const struct xdp_buff *xdp) > > > > I believe this has to return int, not unsigned int. There are places > > where we do data_meta = data + 1, and the callers check whether > > the result is signed or sunsigned. > > The existing SKB APIs are the exact same return type (I copied them 1:1), > but I have a feeling that we’re never intending these values to either A) be > negative and/or B) wrap in strange ways? > > > > >> +{ > >> + return xdp->data - xdp->data_meta; > >> +} > >> + > >> static __always_inline unsigned int > >> xdp_get_buff_len(const struct xdp_buff *xdp) > >> { > >> - unsigned int len = xdp->data_end - xdp->data; > >> + unsigned int len = xdp_headlen(xdp); > >> const struct skb_shared_info *sinfo; > >> > >> if (likely(!xdp_buff_has_frags(xdp))) > >> @@ -364,8 +410,8 @@ int xdp_update_frame_from_buff(const struct xdp_buff *xdp, > >> int metasize, headroom; > > Said another way, perhaps this should be unsigned? > > >> > >> /* Assure headroom is available for storing info */ > >> - headroom = xdp->data - xdp->data_hard_start; > >> - metasize = xdp->data - xdp->data_meta; > >> + headroom = xdp_headroom(xdp); > >> + metasize = xdp_metadata_len(xdp); > >> metasize = metasize > 0 ? metasize : 0; > > > > ^^ like here > > Look across the tree, seems like more are unsigned than signed The ones that are unsigned are either calling xdp_data_meta_unsupported explicitly (and it does > to check for this condition, not signed math) or are running in the drivers that are guaranteed to have metadata support (and, hence, always have data_meta <= data). > These ones use unsigned: > xdp_convert_zc_to_xdp_frame This uses xdp_data_meta_unsupported > veth_xdp_rcv_skb > xsk_construct_skb > bnxt_copy_xdp > i40e_build_skb > i40e_construct_skb_zc > ice_build_skb (this is u8) > ice_construct_skb_zc > igb_build_skb > igb_construct_skb_zc > igc_build_skb > igc_construct_skb > igc_construct_skb_zc > ixgbe_build_skb > ixgbe_construct_skb_zc > ixgbevf_build_skb > mvneta_swbm_build_skb > mlx5e_xsk_construct_skb > mana_build_skb > stmmac_construct_skb_zc > bpf_prog_run_generic_xdp These run in the drivers that support metadata (data_meta <= data) > xdp_get_metalen This uses xdp_data_meta_unsupported > These ones are regular int: > xdp_build_skb_from_buff > xdp_build_skb_from_zc > xdp_update_frame_from_buff > tun_xdp_one > build_skb_from_xdp_buff These can be called from the drivers that support and don't support the metadata, so have to (correctly) use int. > Perhaps a separate patch to convert the regulars to unsigned, > thoughts? Take a look at xdp_set_data_meta_invalid and xdp_data_meta_unsupported. There are cases where xdp->data - xdp->data_meta is -1 (and the callers check for this condition), we can't use unsigned unconditionally (unless we use xdp_data_meta_unsupported).
