diff options
| -rw-r--r-- | share/man/man4/tun.4 | 67 |
1 files changed, 65 insertions, 2 deletions
diff --git a/share/man/man4/tun.4 b/share/man/man4/tun.4 index 2668f68d8d7..9e3a44c2b05 100644 --- a/share/man/man4/tun.4 +++ b/share/man/man4/tun.4 @@ -1,4 +1,4 @@ -.\" $OpenBSD: tun.4,v 1.48 2024/11/17 00:51:04 dlg Exp $ +.\" $OpenBSD: tun.4,v 1.49 2024/11/17 01:44:25 dlg Exp $ .\" .\" Copyright (c) 2003 Marcus D. Watts All rights reserved. .\" @@ -132,6 +132,8 @@ The .Fa tun_if_capabilities field is set with IFCAP values from .In net/if.h . +It is acceptable to enable the offload header without enabling any +interface offload capabilities. .Pp The prepending of network packets with the a .Vt struct tun_hdr @@ -190,7 +192,68 @@ commands: .It Dv SIOCSIFADDR Fa uint8_t Ns [ETHER_ADDR_LEN] Get or set the link layer address (MAC address) of the interface. .El -.\" .Ss Network offload support +.Ss Network offload support +When network offload support has been enabled with the +.Dv TUNSCAP +.Xr ioctl 2 +command, +.Va struct tun_hdr +is prepended to packets read from and written to the device special +file. +.Pp +The kernel will populate the offload header for reads from the +device special file depending on which interface offload capabilities +are enabled. +A program may use any offload feature when writing to the device +special file regardless of which interface offload capabilities are +enabled. +The offload header can be read from one device special file and +written directly to another without interpretation or modification. +.Pp +.Bd -literal +struct tun_hdr { + uint16_t th_flags; + uint16_t th_pad; + uint16_t th_vtag; + uint16_t th_mss; +}; +.Ed +.Pp +The following flags can be set in +.Fa th_flags +to specify which offloads are requested for the current packet: +.Pp +.Bl -tag -width indent -compact +.It Dv TUN_H_VTAG +.Fa th_vtag +is set. +.It Dv TUN_H_TCP_MSS +TCP segmentation offload is requested for the current packet. +The maximum segment size is specified in +.Fa th_mss . +.It Dv TUN_H_IPV4_CSUM +IPv4 header checksum calculation requested. +.It Dv TUN_H_TCP_CSUM +TCP checksum calculation requested. +.It Dv TUN_H_UDP_CSUM +UDP checksum calculation requested. +.It Dv TUN_H_ICMP_CSUM +ICMP checksum calculation requested. +.El +.Pp +Only one of +.Dv TUN_H_TCP_CSUM , +.Dv TUN_H_UDP_CSUM , +and TUN_H_ICMP_CSUM +can be specified at a time. +.Dv TUN_H_VTAG +can only be used with +.Nm tap +interfacse. +.Pp +.Fa th_pad +should be set to 0 when writing to the device special file, and +ignored when reading from the device special file. .Sh FILES .Bl -tag -width /dev/tun* -compact .It Pa /dev/tun* |