How to obtain headers for OpenWRT's kernel ?
There is a relevant Makefile at this link but I can't figure out how to use it.
How to obtain headers for OpenWRT's kernel ?
There is a relevant Makefile at this link but I can't figure out how to use it.
define Host/Configure/all
mkdir -p $(BUILD_DIR_TOOLCHAIN)/linux-dev
$(HOST_KMAKE) \
INSTALL_HDR_PATH="$(BUILD_DIR_TOOLCHAIN)/linux-dev/" \
headers_install
This is the relevant part where we can see more or less where the headers are dropped by the build system. It's a host package so it's in the build folders only, in a folder called "linux-dev" somewhere in the tree.
Looking at a compiled firmware folder (i.e. where the build dirs are populated) I think I find headers in
openwrt/build_dir/toolchain-architecture_name_here-toolchain_name/linux-dev/include/
For example this is a full path from my build folders, for a mipsel system I guess.
openwrt/build_dir/toolchain-mipsel_24kc_gcc-8.3.0_musl/linux-dev/include/
Can you confirm if they are the headers you are looking for?
These are the .h files, which I have in this directory:
user@debian:/home/user/openwrt/build_dir/toolchain-arm_cortex-a15+neon-vfpv4_gcc-7.3.0_musl_eabi/linux-dev/include# find . -type f -name "*.h"
./sound/sb16_csp.h
./sound/snd_sst_tokens.h
./sound/hdsp.h
./sound/emu10k1.h
./sound/asound_fm.h
./sound/compress_params.h
./sound/asoc.h
./sound/hdspm.h
./sound/asound.h
./sound/compress_offload.h
./sound/asequencer.h
./sound/sfnt_info.h
./sound/firewire.h
./sound/usb_stream.h
./sound/tlv.h
./video/sisfb.h
./video/uvesafb.h
./video/edid.h
./misc/cxl.h
./scsi/scsi_bsg_fc.h
./scsi/scsi_netlink.h
./scsi/fc/fc_els.h
./scsi/fc/fc_fs.h
./scsi/fc/fc_gs.h
./scsi/fc/fc_ns.h
./scsi/cxlflash_ioctl.h
./scsi/scsi_netlink_fc.h
./linux/loop.h
./linux/smiapp.h
./linux/fou.h
./linux/devlink.h
./linux/switch.h
./linux/errqueue.h
./linux/elf-fdpic.h
./linux/nubus.h
./linux/mmc/ioctl.h
./linux/nfsd/debug.h
./linux/nfsd/cld.h
./linux/nfsd/export.h
./linux/nfsd/stats.h
./linux/nfsd/nfsfh.h
./linux/ip6_tunnel.h
./linux/seccomp.h
./linux/isdn_divertif.h
./linux/if_packet.h
./linux/usb/charger.h
./linux/usb/cdc.h
./linux/usb/ch9.h
./linux/usb/g_printer.h
./linux/usb/functionfs.h
./linux/usb/tmc.h
./linux/usb/audio.h
./linux/usb/gadgetfs.h
./linux/usb/midi.h
./linux/usb/ch11.h
./linux/usb/video.h
./linux/usb/cdc-wdm.h
./linux/coda.h
./linux/phonet.h
./linux/cec.h
./linux/sunrpc/debug.h
./linux/mtio.h
./linux/kernelcapi.h
./linux/unix_diag.h
./linux/vhost.h
./linux/bpf.h
./linux/xilinx-v4l2-controls.h
./linux/audit.h
./linux/netfilter.h
./linux/eventpoll.h
./linux/acct.h
./linux/ptrace.h
./linux/kcm.h
./linux/agpgart.h
./linux/pci_regs.h
./linux/ppp_defs.h
./linux/atmlec.h
./linux/switchtec_ioctl.h
./linux/module.h
./linux/const.h
./linux/if_tun.h
./linux/thermal.h
./linux/blkpg.h
./linux/ipv6.h
./linux/seg6_genl.h
./linux/netfilter_ipv4.h
./linux/tc_ematch/tc_em_text.h
./linux/tc_ematch/tc_em_meta.h
./linux/tc_ematch/tc_em_nbyte.h
./linux/tc_ematch/tc_em_cmp.h
./linux/netfilter_ipv6.h
./linux/media-bus-format.h
./linux/virtio_console.h
./linux/elf.h
./linux/tty.h
./linux/tls.h
./linux/phantom.h
./linux/wimax.h
./linux/atm_idt77105.h
./linux/kexec.h
./linux/hyperv.h
./linux/omapfb.h
./linux/icmp.h
./linux/random.h
./linux/virtio_crypto.h
./linux/nfs.h
./linux/irda.h
./linux/auto_dev-ioctl.h
./linux/nsfs.h
./linux/hw_breakpoint.h
./linux/net_namespace.h
./linux/atmmpc.h
./linux/pkt_cls.h
./linux/netfilter_ipv4/ipt_ecn.h
./linux/netfilter_ipv4/ipt_ah.h
./linux/netfilter_ipv4/ipt_ECN.h
./linux/netfilter_ipv4/ipt_TTL.h
./linux/netfilter_ipv4/ipt_ttl.h
./linux/netfilter_ipv4/ipt_LOG.h
./linux/netfilter_ipv4/ipt_REJECT.h
./linux/netfilter_ipv4/ipt_CLUSTERIP.h
./linux/netfilter_ipv4/ip_tables.h
./linux/timerfd.h
./linux/mempolicy.h
./linux/userfaultfd.h
./linux/dcbnl.h
./linux/atm_he.h
./linux/tc_act/tc_ife.h
./linux/tc_act/tc_ipt.h
./linux/tc_act/tc_csum.h
./linux/tc_act/tc_gact.h
./linux/tc_act/tc_mirred.h
./linux/tc_act/tc_vlan.h
./linux/tc_act/tc_connmark.h
./linux/tc_act/tc_defact.h
./linux/tc_act/tc_skbedit.h
./linux/tc_act/tc_pedit.h
./linux/tc_act/tc_tunnel_key.h
./linux/tc_act/tc_nat.h
./linux/tc_act/tc_bpf.h
./linux/tc_act/tc_sample.h
./linux/tc_act/tc_skbmod.h
./linux/posix_acl_xattr.h
./linux/veth.h
./linux/can/error.h
./linux/can/netlink.h
./linux/can/raw.h
./linux/can/bcm.h
./linux/can/gw.h
./linux/can/vxcan.h
./linux/pmu.h
./linux/netrom.h
./linux/soundcard.h
./linux/snmp.h
./linux/ip.h
./linux/socket.h
./linux/parport.h
./linux/inotify.h
./linux/timex.h
./linux/dlm.h
./linux/resource.h
./linux/media.h
./linux/sysinfo.h
./linux/termios.h
./linux/v4l2-mediabus.h
./linux/v4l2-subdev.h
./linux/flat.h
./linux/fdreg.h
./linux/nfc.h
./linux/nfs_fs.h
./linux/udf_fs_i.h
./linux/times.h
./linux/if_ether.h
./linux/mmtimer.h
./linux/sdla.h
./linux/virtio_9p.h
./linux/limits.h
./linux/atm_nicstar.h
./linux/nfs_mount.h
./linux/coff.h
./linux/uhid.h
./linux/gfs2_ondisk.h
./linux/membarrier.h
./linux/virtio_mmio.h
./linux/if_cablemodem.h
./linux/hiddev.h
./linux/virtio_ids.h
./linux/virtio_ring.h
./linux/lirc.h
./linux/hsi/cs-protocol.h
./linux/hsi/hsi_char.h
./linux/kcov.h
./linux/genetlink.h
./linux/tcp_metrics.h
./linux/seg6.h
./linux/pktcdvd.h
./linux/ax25.h
./linux/gigaset_dev.h
./linux/reiserfs_xattr.h
./linux/tipc_config.h
./linux/fsl_hypervisor.h
./linux/cramfs_fs.h
./linux/dvb/osd.h
./linux/dvb/ca.h
./linux/dvb/net.h
./linux/dvb/audio.h
./linux/dvb/dmx.h
./linux/dvb/frontend.h
./linux/dvb/video.h
./linux/dvb/version.h
./linux/byteorder/big_endian.h
./linux/byteorder/little_endian.h
./linux/hdlcdrv.h
./linux/nfs_idmap.h
./linux/mroute.h
./linux/hdlc.h
./linux/sem.h
./linux/bpf_common.h
./linux/dm-log-userspace.h
./linux/jffs2.h
./linux/atmarp.h
./linux/igmp.h
./linux/if_ppp.h
./linux/nl80211.h
./linux/poll.h
./linux/btrfs_tree.h
./linux/isdn_ppp.h
./linux/i2o-dev.h
./linux/if_fddi.h
./linux/gen_stats.h
./linux/connector.h
./linux/zorro.h
./linux/rtc.h
./linux/atmbr2684.h
./linux/cm4000_cs.h
./linux/ppp-comp.h
./linux/rds.h
./linux/rpmsg.h
./linux/aspeed-lpc-ctrl.h
./linux/if_hippi.h
./linux/tee.h
./linux/dqblk_xfs.h
./linux/x25.h
./linux/qnx4_fs.h
./linux/psample.h
./linux/cuda.h
./linux/i2c.h
./linux/romfs_fs.h
./linux/in.h
./linux/lightnvm.h
./linux/elfcore.h
./linux/videodev2.h
./linux/if_bonding.h
./linux/raid/md_p.h
./linux/raid/md_u.h
./linux/scif_ioctl.h
./linux/serial_core.h
./linux/fsmap.h
./linux/n_r3964.h
./linux/if_bridge.h
./linux/keyboard.h
./linux/fib_rules.h
./linux/stat.h
./linux/usbdevice_fs.h
./linux/adfs_fs.h
./linux/netdevice.h
./linux/tcp.h
./linux/gsmmux.h
./linux/types.h
./linux/virtio_pci.h
./linux/if_pppol2tp.h
./linux/zorro_ids.h
./linux/efs_fs_sb.h
./linux/msdos_fs.h
./linux/serio.h
./linux/isdnif.h
./linux/atmapi.h
./linux/cec-funcs.h
./linux/lwtunnel.h
./linux/mii.h
./linux/if_addrlabel.h
./linux/if_arcnet.h
./linux/perf_event.h
./linux/binfmts.h
./linux/ptp_clock.h
./linux/if_pppox.h
./linux/atmioc.h
./linux/ivtvfb.h
./linux/input.h
./linux/ppp-ioctl.h
./linux/baycom.h
./linux/kfd_ioctl.h
./linux/uleds.h
./linux/nfs3.h
./linux/xfrm.h
./linux/v4l2-common.h
./linux/elf-em.h
./linux/wireless.h
./linux/rio_cm_cdev.h
./linux/netlink.h
./linux/v4l2-controls.h
./linux/edd.h
./linux/adb.h
./linux/stddef.h
./linux/iso_fs.h
./linux/seg6_iptunnel.h
./linux/hsr_netlink.h
./linux/fadvise.h
./linux/virtio_balloon.h
./linux/affs_hardblocks.h
./linux/smc_diag.h
./linux/signalfd.h
./linux/utsname.h
./linux/aio_abi.h
./linux/dm-ioctl.h
./linux/magic.h
./linux/mdio.h
./linux/net.h
./linux/map_to_7segment.h
./linux/am437x-vpfe.h
./linux/sed-opal.h
./linux/chio.h
./linux/netfilter/xt_devgroup.h
./linux/netfilter/xt_IDLETIMER.h
./linux/netfilter/xt_connbytes.h
./linux/netfilter/xt_helper.h
./linux/netfilter/xt_LOG.h
./linux/netfilter/xt_cgroup.h
./linux/netfilter/nf_conntrack_common.h
./linux/netfilter/xt_connmark.h
./linux/netfilter/nfnetlink_compat.h
./linux/netfilter/xt_FLOWOFFLOAD.h
./linux/netfilter/xt_AUDIT.h
./linux/netfilter/nf_conntrack_ftp.h
./linux/netfilter/x_tables.h
./linux/netfilter/xt_conntrack.h
./linux/netfilter/xt_hashlimit.h
./linux/netfilter/xt_set.h
./linux/netfilter/xt_RATEEST.h
./linux/netfilter/xt_state.h
./linux/netfilter/xt_MARK.h
./linux/netfilter/xt_mac.h
./linux/netfilter/xt_policy.h
./linux/netfilter/xt_CONNMARK.h
./linux/netfilter/xt_rateest.h
./linux/netfilter/xt_connlimit.h
./linux/netfilter/xt_esp.h
./linux/netfilter/nfnetlink.h
./linux/netfilter/nfnetlink_conntrack.h
./linux/netfilter/xt_dccp.h
./linux/netfilter/xt_cpu.h
./linux/netfilter/xt_quota.h
./linux/netfilter/xt_rpfilter.h
./linux/netfilter/xt_HMARK.h
./linux/netfilter/xt_SECMARK.h
./linux/netfilter/xt_iprange.h
./linux/netfilter/xt_string.h
./linux/netfilter/xt_realm.h
./linux/netfilter/xt_TCPOPTSTRIP.h
./linux/netfilter/xt_statistic.h
./linux/netfilter/xt_TEE.h
./linux/netfilter/nf_conntrack_tcp.h
./linux/netfilter/ipset/ip_set_bitmap.h
./linux/netfilter/ipset/ip_set.h
./linux/netfilter/ipset/ip_set_hash.h
./linux/netfilter/ipset/ip_set_list.h
./linux/netfilter/xt_CONNSECMARK.h
./linux/netfilter/nfnetlink_log.h
./linux/netfilter/xt_NFQUEUE.h
./linux/netfilter/xt_limit.h
./linux/netfilter/xt_CT.h
./linux/netfilter/nf_tables_compat.h
./linux/netfilter/xt_CLASSIFY.h
./linux/netfilter/nfnetlink_queue.h
./linux/netfilter/xt_tcpmss.h
./linux/netfilter/nf_nat.h
./linux/netfilter/xt_ipvs.h
./linux/netfilter/xt_time.h
./linux/netfilter/xt_SYNPROXY.h
./linux/netfilter/nf_log.h
./linux/netfilter/xt_length.h
./linux/netfilter/xt_ecn.h
./linux/netfilter/xt_physdev.h
./linux/netfilter/xt_osf.h
./linux/netfilter/xt_l2tp.h
./linux/netfilter/xt_sctp.h
./linux/netfilter/xt_dscp.h
./linux/netfilter/nf_conntrack_tuple_common.h
./linux/netfilter/xt_connlabel.h
./linux/netfilter/xt_u32.h
./linux/netfilter/xt_ipcomp.h
./linux/netfilter/xt_socket.h
./linux/netfilter/xt_mark.h
./linux/netfilter/xt_LED.h
./linux/netfilter/xt_multiport.h
./linux/netfilter/nfnetlink_cttimeout.h
./linux/netfilter/nfnetlink_cthelper.h
./linux/netfilter/nfnetlink_acct.h
./linux/netfilter/xt_tcpudp.h
./linux/netfilter/xt_addrtype.h
./linux/netfilter/xt_CHECKSUM.h
./linux/netfilter/nf_conntrack_sctp.h
./linux/netfilter/xt_recent.h
./linux/netfilter/xt_comment.h
./linux/netfilter/xt_TPROXY.h
./linux/netfilter/xt_DSCP.h
./linux/netfilter/nf_tables.h
./linux/netfilter/xt_pkttype.h
./linux/netfilter/xt_NFLOG.h
./linux/netfilter/xt_TCPMSS.h
./linux/netfilter/xt_cluster.h
./linux/netfilter/xt_nfacct.h
./linux/netfilter/xt_owner.h
./linux/netfilter/xt_bpf.h
./linux/kernel.h
./linux/seg6_local.h
./linux/mqueue.h
./linux/virtio_rng.h
./linux/ethtool.h
./linux/virtio_blk.h
./linux/reboot.h
./linux/raw.h
./linux/atmsap.h
./linux/max2175.h
./linux/iio/types.h
./linux/iio/events.h
./linux/signal.h
./linux/qrtr.h
./linux/sound.h
./linux/if.h
./linux/mic_ioctl.h
./linux/errno.h
./linux/in_route.h
./linux/tipc_netlink.h
./linux/dma-buf.h
./linux/inet_diag.h
./linux/pcitest.h
./linux/pg.h
./linux/nvram.h
./linux/time.h
./linux/pfkeyv2.h
./linux/qnxtypes.h
./linux/nfs4.h
./linux/xattr.h
./linux/gpio.h
./linux/sync_file.h
./linux/if_ltalk.h
./linux/can.h
./linux/blkzoned.h
./linux/if_eql.h
./linux/rio_mport_cdev.h
./linux/cifs/cifs_mount.h
./linux/dlmconstants.h
./linux/fiemap.h
./linux/kdev_t.h
./linux/hash_info.h
./linux/if_arp.h
./linux/kernel-page-flags.h
./linux/virtio_input.h
./linux/virtio_config.h
./linux/sock_diag.h
./linux/blktrace_api.h
./linux/keyctl.h
./linux/nbd.h
./linux/fuse.h
./linux/hidraw.h
./linux/suspend_ioctls.h
./linux/uvcvideo.h
./linux/gameport.h
./linux/rfkill.h
./linux/telephony.h
./linux/auto_fs4.h
./linux/v4l2-dv-timings.h
./linux/bpqether.h
./linux/smc.h
./linux/futex.h
./linux/atm.h
./linux/reiserfs_fs.h
./linux/libc-compat.h
./linux/nvme_ioctl.h
./linux/psci.h
./linux/hdreg.h
./linux/bt-bmc.h
./linux/meye.h
./linux/netfilter_arp.h
./linux/net_dropmon.h
./linux/ipv6_route.h
./linux/if_slip.h
./linux/netfilter_arp/arp_tables.h
./linux/netfilter_arp/arpt_mangle.h
./linux/ixjuser.h
./linux/ipx.h
./linux/nilfs2_api.h
./linux/mman.h
./linux/input-event-codes.h
./linux/rtnetlink.h
./linux/sched/types.h
./linux/mei.h
./linux/ncp.h
./linux/atmclip.h
./linux/ivtv.h
./linux/nfsacl.h
./linux/i8k.h
./linux/virtio_net.h
./linux/vm_sockets.h
./linux/cdrom.h
./linux/shm.h
./linux/if_infiniband.h
./linux/msg.h
./linux/ncp_no.h
./linux/capability.h
./linux/sched.h
./linux/matroxfb.h
./linux/rxrpc.h
./linux/ncp_fs.h
./linux/scc.h
./linux/if_plip.h
./linux/vt.h
./linux/fb.h
./linux/llc.h
./linux/sockios.h
./linux/auto_fs.h
./linux/icmpv6.h
./linux/capi.h
./linux/hysdn_if.h
./linux/ife.h
./linux/virtio_types.h
./linux/atm_eni.h
./linux/android/binder.h
./linux/personality.h
./linux/dn.h
./linux/wimax/i2400m.h
./linux/l2tp.h
./linux/nfs2.h
./linux/arcfb.h
./linux/major.h
./linux/route.h
./linux/atalk.h
./linux/kvm.h
./linux/falloc.h
./linux/screen_info.h
./linux/fd.h
./linux/hdlc/ioctl.h
./linux/ultrasound.h
./linux/bfs_fs.h
./linux/hpet.h
./linux/netfilter_bridge/ebt_nflog.h
./linux/netfilter_bridge/ebt_arpreply.h
./linux/netfilter_bridge/ebtables.h
./linux/netfilter_bridge/ebt_ip.h
./linux/netfilter_bridge/ebt_redirect.h
./linux/netfilter_bridge/ebt_mark_m.h
./linux/netfilter_bridge/ebt_mark_t.h
./linux/netfilter_bridge/ebt_ip6.h
./linux/netfilter_bridge/ebt_vlan.h
./linux/netfilter_bridge/ebt_stp.h
./linux/netfilter_bridge/ebt_802_3.h
./linux/netfilter_bridge/ebt_nat.h
./linux/netfilter_bridge/ebt_among.h
./linux/netfilter_bridge/ebt_log.h
./linux/netfilter_bridge/ebt_pkttype.h
./linux/netfilter_bridge/ebt_arp.h
./linux/netfilter_bridge/ebt_limit.h
./linux/dlm_netlink.h
./linux/toshiba.h
./linux/bpf_perf_event.h
./linux/coresight-stm.h
./linux/un.h
./linux/sctp.h
./linux/pr.h
./linux/mic_common.h
./linux/seg6_hmac.h
./linux/if_addr.h
./linux/cgroupstats.h
./linux/cryptouser.h
./linux/lp.h
./linux/ipmi.h
./linux/swab.h
./linux/isdn/capicmd.h
./linux/sysctl.h
./linux/pci.h
./linux/if_alg.h
./linux/fcntl.h
./linux/tiocl.h
./linux/openvswitch.h
./linux/mpls_iptunnel.h
./linux/bcache.h
./linux/virtio_scsi.h
./linux/usbip.h
./linux/cycx_cfm.h
./linux/wait.h
./linux/pkt_sched.h
./linux/ndctl.h
./linux/atmdev.h
./linux/netconf.h
./linux/utime.h
./linux/posix_acl.h
./linux/if_x25.h
./linux/genwqe/genwqe_card.h
./linux/irqnr.h
./linux/if_phonet.h
./linux/if_vlan.h
./linux/cyclades.h
./linux/oom.h
./linux/cn_proc.h
./linux/netlink_diag.h
./linux/nbd-netlink.h
./linux/memfd.h
./linux/target_core_user.h
./linux/virtio_gpu.h
./linux/joystick.h
./linux/firewire-cdev.h
./linux/ila.h
./linux/ipsec.h
./linux/selinux_netlink.h
./linux/param.h
./linux/patchkey.h
./linux/if_link.h
./linux/vfio.h
./linux/cciss_defs.h
./linux/minix_fs.h
./linux/taskstats.h
./linux/ppdev.h
./linux/if_frad.h
./linux/netfilter_decnet.h
./linux/netfilter_ipv6/ip6_tables.h
./linux/netfilter_ipv6/ip6t_LOG.h
./linux/netfilter_ipv6/ip6t_HL.h
./linux/netfilter_ipv6/ip6t_hl.h
./linux/netfilter_ipv6/ip6t_mh.h
./linux/netfilter_ipv6/ip6t_REJECT.h
./linux/netfilter_ipv6/ip6t_opts.h
./linux/netfilter_ipv6/ip6t_ah.h
./linux/netfilter_ipv6/ip6t_NPT.h
./linux/netfilter_ipv6/ip6t_ipv6header.h
./linux/netfilter_ipv6/ip6t_rt.h
./linux/netfilter_ipv6/ip6t_frag.h
./linux/ipmi_msgdefs.h
./linux/ncp_mount.h
./linux/coda_psdev.h
./linux/if_macsec.h
./linux/dccp.h
./linux/rose.h
./linux/spi/spidev.h
./linux/firewire-constants.h
./linux/prctl.h
./linux/securebits.h
./linux/uuid.h
./linux/ip_vs.h
./linux/radeonfb.h
./linux/virtio_vsock.h
./linux/atmppp.h
./linux/fanotify.h
./linux/apm_bios.h
./linux/pps.h
./linux/cciss_ioctl.h
./linux/uinput.h
./linux/udp.h
./linux/sonypi.h
./linux/bsg.h
./linux/vtpm_proxy.h
./linux/auxvec.h
./linux/neighbour.h
./linux/if_tunnel.h
./linux/serial_reg.h
./linux/bcm933xx_hcs.h
./linux/caif/caif_socket.h
./linux/caif/if_caif.h
./linux/vsockmon.h
./linux/dlm_plock.h
./linux/gtp.h
./linux/serial.h
./linux/atm_zatm.h
./linux/vfio_ccw.h
./linux/wanrouter.h
./linux/b1lli.h
./linux/unistd.h
./linux/atm_tcp.h
./linux/btrfs.h
./linux/filter.h
./linux/net_tstamp.h
./linux/stm.h
./linux/i2c-dev.h
./linux/nilfs2_ondisk.h
./linux/dlm_device.h
./linux/mroute6.h
./linux/if_team.h
./linux/ioctl.h
./linux/tty_flags.h
./linux/omap3isp.h
./linux/posix_types.h
./linux/isdn.h
./linux/packet_diag.h
./linux/fs.h
./linux/kd.h
./linux/atmsvc.h
./linux/tipc.h
./linux/if_fc.h
./linux/kcmp.h
./linux/ipc.h
./linux/quota.h
./linux/mpls.h
./linux/batman_adv.h
./linux/kvm_para.h
./linux/string.h
./linux/sonet.h
./linux/userio.h
./linux/synclink.h
./linux/uio.h
./linux/in6.h
./linux/watchdog.h
./linux/nfs4_mount.h
./linux/hid.h
./linux/version.h
./linux/netfilter_bridge.h
./mtd/mtd-abi.h
./mtd/inftl-user.h
./mtd/mtd-user.h
./mtd/nftl-user.h
./mtd/ubi-user.h
./rdma/rdma_user_ioctl.h
./rdma/qedr-abi.h
./rdma/rdma_user_rxe.h
./rdma/ib_user_mad.h
./rdma/ib_user_ioctl_verbs.h
./rdma/hfi/hfi1_user.h
./rdma/hfi/hfi1_ioctl.h
./rdma/mthca-abi.h
./rdma/rdma_user_cm.h
./rdma/mlx4-abi.h
./rdma/mlx5-abi.h
./rdma/rdma_netlink.h
./rdma/ib_user_cm.h
./rdma/cxgb3-abi.h
./rdma/ocrdma-abi.h
./rdma/ib_user_verbs.h
./rdma/vmw_pvrdma-abi.h
./rdma/bnxt_re-abi.h
./rdma/hns-abi.h
./rdma/nes-abi.h
./rdma/ib_user_sa.h
./rdma/cxgb4-abi.h
./asm/ptrace.h
./asm/socket.h
./asm/sigcontext.h
./asm/perf_regs.h
./asm/resource.h
./asm/setup.h
./asm/termios.h
./asm/unistd-eabi.h
./asm/termbits.h
./asm/ipcbuf.h
./asm/hwcap.h
./asm/sembuf.h
./asm/unistd-common.h
./asm/poll.h
./asm/statfs.h
./asm/stat.h
./asm/types.h
./asm/msgbuf.h
./asm/ioctls.h
./asm/signal.h
./asm/errno.h
./asm/mman.h
./asm/siginfo.h
./asm/bitsperlong.h
./asm/sockios.h
./asm/kvm.h
./asm/byteorder.h
./asm/swab.h
./asm/fcntl.h
./asm/param.h
./asm/unistd-oabi.h
./asm/auxvec.h
./asm/unistd.h
./asm/ioctl.h
./asm/posix_types.h
./asm/shmbuf.h
./asm/kvm_para.h
./xen/gntdev.h
./xen/gntalloc.h
./xen/privcmd.h
./xen/evtchn.h
./drm/vc4_drm.h
./drm/drm.h
./drm/tegra_drm.h
./drm/armada_drm.h
./drm/mga_drm.h
./drm/nouveau_drm.h
./drm/sis_drm.h
./drm/omap_drm.h
./drm/exynos_drm.h
./drm/i810_drm.h
./drm/drm_mode.h
./drm/via_drm.h
./drm/drm_sarea.h
./drm/amdgpu_drm.h
./drm/savage_drm.h
./drm/msm_drm.h
./drm/vgem_drm.h
./drm/radeon_drm.h
./drm/drm_fourcc.h
./drm/qxl_drm.h
./drm/virtgpu_drm.h
./drm/r128_drm.h
./drm/i915_drm.h
./drm/vmwgfx_drm.h
./drm/etnaviv_drm.h
./asm-generic/mman-common.h
./asm-generic/socket.h
./asm-generic/resource.h
./asm-generic/setup.h
./asm-generic/termios.h
./asm-generic/termbits.h
./asm-generic/ipcbuf.h
./asm-generic/sembuf.h
./asm-generic/signal-defs.h
./asm-generic/poll.h
./asm-generic/statfs.h
./asm-generic/stat.h
./asm-generic/int-ll64.h
./asm-generic/shmparam.h
./asm-generic/types.h
./asm-generic/msgbuf.h
./asm-generic/ioctls.h
./asm-generic/signal.h
./asm-generic/errno.h
./asm-generic/int-l64.h
./asm-generic/ucontext.h
./asm-generic/mman.h
./asm-generic/siginfo.h
./asm-generic/hugetlb_encode.h
./asm-generic/bitsperlong.h
./asm-generic/sockios.h
./asm-generic/swab.h
./asm-generic/fcntl.h
./asm-generic/errno-base.h
./asm-generic/param.h
./asm-generic/auxvec.h
./asm-generic/unistd.h
./asm-generic/ioctl.h
./asm-generic/posix_types.h
./asm-generic/shmbuf.h
./asm-generic/kvm_para.h
That's more or less similar to the content I have on mine, and I know what "headers" are in C, those are definitely header files.
I don't know if that's enough to compile a kernel module. I never used Linux From Scratch, I don't know how to compile a kernel (or kernel module) manually.
Are these the headers after the OpenWRT's patches are applied to the vanilla kernel sources ...or before?
It does not seem to do any patching to these files, only "install" into that folder.
Another place where you find headers is (example from my build folders)
openwrt/build_dir/target-arm_cortex-a7+neon-vfpv4_musl_eabi/linux-ipq40xx_generic/linux-4.19.88/user_headers/include/
as stated in thhis part of the build system https://github.com/openwrt/openwrt/blob/master/include/kernel-defaults.mk#L107
These are the only two places you will find headers in, for each architecture/target you compile.
I don't know if they are patched or not, I guess you will have to find out by checksumming the files to see if they are different in the two folders
You can also try to ask in the mailing list or IRC chat as there is where actual OpenWrt developers mostly are.
Start with this (package/custom/devel/kernel-headers/Makefile):
include $(TOPDIR)/rules.mk
# Be sure to sync version with kernel version
include $(INCLUDE_DIR)/package.mk
include $(INCLUDE_DIR)/kernel.mk
PKG_NAME:=kernel-headers
PKG_VERSION:=$(LINUX_VERSION)-$(LINUX_RELEASE)-$(LINUX_VERMAGIC)
PKG_RELEASE:=1
define Package/$(PKG_NAME)
SECTION:=devel
CATEGORY:=Development
TITLE:=kernel-headers (Development headers)
DEPENDS:=+libncursesw +xz +coreutils-whoami +libelf
URL:=http://www.kernel.org/
endef
define Package/$(PKG_NAME)/description
kernel-headers files for development
endef
# Prepare, Configure, Compile already done by kernel depends
define Build/Prepare
endef
define Build/Configure
endef
define Build/Compile
endef
# Fails on libtinfo.so.5 dependency. Disable dependency checking
#define CheckDependencies
#endef
# Determine gcc version
GCC_VERSION:=$(call qstrip,$(CONFIG_GCC_VERSION))
# Same version as in feeds/packages/devel/gcc/Makefile
GCC_VER:=7.4.0
define Package/$(PKG_NAME)/install
echo INSTALL_DIR: /usr/src/linux-$(LINUX_VERSION)
echo SRC_DIR: $(LINUX_DIR)/
echo STDARG_LOCATION: /usr/gcc-$(GCC_VER)/lib/gcc/$(REAL_GNU_TARGET_NAME)/$(GCC_VER)/include/stdarg.h
echo STDARG_LINK: /usr/src/linux-$(LINUX_VERSION)/include/stdarg.h
$(INSTALL_DIR) $(1)/usr/src/linux-$(LINUX_VERSION)
cp $(LINUX_DIR)/.config $(1)/usr/src/linux-$(LINUX_VERSION)
$(CP) $(LINUX_DIR)/* $(1)/usr/src/linux-$(LINUX_VERSION)
endef
define Package/$(PKG_NAME)/postinst
#!/bin/sh
# Some compiles fail without this link to stdarg.h
ln -sf /usr/lib/gcc/$(REAL_GNU_TARGET_NAME)/$(GCC_VER)/include/stdarg.h /usr/src/linux-$(LINUX_VERSION)/include/stdarg.h
ln -sf /usr/src/linux-$(LINUX_VERSION) /lib/modules/$(LINUX_VERSION)/build
endef
$(eval $(call BuildPackage,$(PKG_NAME)))