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Extend the description of the framework of interface capabilities.

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This commit is contained in:
Yaroslav Tykhiy 2004-01-22 00:10:21 +00:00
parent 76f80df62e
commit d4030ed6c5
1 changed files with 90 additions and 4 deletions
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94
share/man/man9/ifnet.9
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@ -470,8 +470,18 @@ Interface capabilities are specialized features an interface may
or may not support.
These capabilities are very hardware-specific
and allow, when enabled,
to offload specific network processing to the interface.
.Bl -tag -width ".Dv IFCAP_NETCONS" -offset indent
to offload specific network processing to the interface
or to offer a particular feature for use by upper layers.
.Pp
It should be noted that a capability can be completely
uncontrolled (i.e., stay always enabled with no way to disable it)
or allow limited control over itself (e.g., depend on another
capability's state.)
Such peculiarities are determined solely by the hardware and driver
of a particular interface.
.Pp
The following capabilities are currently supported by the system:
.Bl -tag -width ".Dv IFCAP_VLAN_HWTAGGING" -offset indent
.It Dv IFCAP_NETCONS
This interface can be a network console.
.It Dv IFCAP_RXCSUM
@ -482,7 +492,74 @@ The driver for the interface might disable hardware checksum validation
if the MTU is set above the hardcoded limit.
.It Dv IFCAP_TXCSUM
This interface can do checksum calculation on transmitting data.
.It Dv IFCAP_HWCSUM
A shorthand for
.Dq Dv IFCAP_RXCSUM | Dv IFCAP_TXCSUM .
.It Dv IFCAP_VLAN_HWTAGGING
This interface can do VLAN tagging on output and
demultiplex frames by their VLAN tag on input.
.It Dv IFCAP_VLAN_MTU
The
.Xr vlan 4
driver can operate over this interface in software tagging mode
without having to decrease MTU on
.Xr vlan 4
interfaces below 1500 bytes.
This implies the ability of this interface to cope with frames somewhat
longer than permitted by the Ethernet specification.
.It Dv IFCAP_JUMBO_MTU
This Ethernet interface can transmit and receive frames up to
9000 bytes long.
.El
.Pp
The ability of advanced network interfaces to offload certain
computational tasks from the host CPU to the board is limited
mostly to TCP/IP.
Therefore a separate field associated with an interface
(see
.Va ifnet.if_data.ifi_hwassist
below)
keeps a detailed description of its enabled capabilities
specific to TCP/IP processing.
The TCP/IP module consults the field to see which tasks
can be done on an
.Em outgoing
packet by the interface.
The flags defined for that field are a superset of those for
.Va mbuf.m_pkthdr.csum_flags ,
namely:
.Bl -tag -width ".Dv CSUM_FRAGMENT" -offset indent
.It Dv CSUM_IP
The interface will compute IP checksums.
.It Dv CSUM_TCP
The interface will compute TCP checksums.
.It Dv CSUM_UDP
The interface will compute UDP checksums.
.It Dv CSUM_IP_FRAGS
The interface can compute a TCP or UDP checksum for a packet
fragmented by the host CPU.
Makes sense only along with
.Dv CSUM_TCP
or
.Dv CSUM_UDP .
.It Dv CSUM_FRAGMENT
The interface will do the fragmentation of IP packets if necessary.
The host CPU doesn't need to care about MTU on this interface
as long as a packet to transmit through it is an IP one and it
doesn't exceed the size of the hardware buffer.
.El
.Pp
An interface notifies the TCP/IP module about the tasks
the former has performed on an
.Em incoming
packet by setting the corresponding flags in the field
.Va mbuf.m_pkthdr.csum_flags
of the
.Vt mbuf chain
containing the packet.
See
.Xr mbuf 9
for details.
.Ss The Vt if_data Ss Structure
In
.Bx 4.4 ,
@ -549,6 +626,15 @@ A dimensionless metric interpreted by a user-mode routing process.
.It Va ifi_baudrate
.Pq Vt u_long
The line rate of the interface, in bits per second.
.It Va ifi_hwassist
.Pq Vt u_long
A detailed interpretation of the capabilities
to offload computational tasks for
.Em outgoing
packets.
The interface driver must keep this field in accord with
the current value of
.Va if_capenable .
.El
.Pp
The structure additionally contains generic statistics applicable to a
@ -873,7 +959,7 @@ Get interface capabilities, flags, metric, MTU, medium selection.
(No call-down to driver.)
.Pp
.It Dv SIOCSIFCAP
Enable interface capabilities.
Enable or disable interface capabilities.
Caller must have appropriate privilege.
.Pp
.It Dv SIOCSIFFLAGS
@ -1068,7 +1154,7 @@ if one is found, else it returns a null pointer.
.Xr netintro 4 ,
.Xr config 8 ,
.Xr ppp 8 ,
.\" .Xr mbuf 9 ,
.Xr mbuf 9 ,
.Xr rtentry 9
.Rs
.%A Gary R. Wright