.\" Copyright (c) 2012-2013 Luigi Rizzo, Universita` di Pisa
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.\" This document is derived in part from the enet man page (enet.4)
.\" distributed with 4.3BSD Unix.
.\"
.\" $FreeBSD: head/share/man/man4/vale.4 228017 2011-11-27 06:55:57Z gjb $
.\"
.Dd December 26, 2013
.Dt VALE 4
.Os
.Sh NAME
.Nm vale
.Nd a very fast Virtual Local Ethernet using the netmap API
.Sh SYNOPSIS
.Cd device netmap
.Sh DESCRIPTION
.Nm
is a feature of the
.Xr netmap 4
module that implements multiple virtual switches that can
be used to interconnect
.Xr netmap 4
clients, including traffic sources and sinks, packet forwarders,
userspace firewalls, and so on.
.Pp
.Nm
is implemented completely in software, and is extremely fast.
On a modern machine it can move almost 20 Million packets per
second (Mpps) per core with small frames, and about 70 Gbit/s
with 1500 byte frames.
.Sh OPERATION
.Nm
dynamically creates switches and ports as client connect
to it using the
.Xr netmap 4
API.
.Pp
.Nm
ports are named
.Pa vale[bdg:][port]
where
.Pa vale
is the prefix indicating a VALE switch rather than a standard interface,
.Pa bdg
indicates a specific switch (the colon is a separator),
and
.Pa port
indicates a port within the switch.
Bridge and ports names are arbitrary strings, the only
constraint being that the full name must fit within 16
characters.
.Pp
.Nm
ports can be physical network interfaces that support the
.Xr netmap 4
API
by specifying the interface name for
.Pa [port] .
See
.Xr netmap 4
for details of the naming rule.
.Pp
Physical interfaces are attached using the
.Dv NIOCGREGIF
command of
.Xr ioctl 2 ,
and
.Dv NETMAP_BDG_ATTACH
for the
.Va nr_cmd
field in
.Vt struct nmreq .
The corresponding host stack can also be attached to the bridge, specifying
.Dv NETMAP_BDG_HOST
in
.Va nr_arg1 .
To detach the interface from the bridge,
.Dv NETMAP_BDG_DETACH
is used instead of
.Dv NETMAP_BDG_ATTACH .
The host stack is also detached from the bridge at the same
time if it had been attached.
.Pp
Physical interfaces are treated as a system configuration;
they remain attached even after the configuring process died,
and can be detached by any other process.
.Pp
Once a physical interface is attached, this interface is no longer
available to be directly accessed by
.Xr netmap 4
clients (user processes) or to be attached by another bridge.
On the other hand, when a
.Xr netmap 4
client holds the physical interface,
this interface cannot be attached to a bridge.
.Pp
.Va NETMAP_BDG_LIST
subcommand in
.Va nr_cmd
of
.Vt struct nmreq
is used to obtain bridge and port information.
There are two modes of how this works.
If any
.Va nr_name
starting from non '\\0' is provided,
.Xr ioctl 2
returning indicates the position of the named interface.
This position is represented by an index of the bridge and the port,
and put into the
.Va nr_arg1
and
.Va nr_arg2
fields, respectively.
If the named interface does not exist,
.Xr ioctl 2
returns
.Dv EINVAL .
.Pp
If
.Va nr_name
starting from '\\0' is provided,
.Xr ioctl 2
returning indicates the
first existing interface on and after the position specified in
.Va nr_arg1
and
.Va nr_arg2 .
If the caller specified a port index greater than the highest
index of the ports, it is recognized as port index 0 of the
next bridge (
.Va nr_arg1
+ 1,
.Va nr_arg2
= 0).
.Xr ioctl 2
returns
.Dv EINVAL
if the given position is higher than that of
any existing interface.
On successful return of
.Xr ioctl 2 ,
the interface name is also stored in
.Va nr_name .
.Dv NETMAP_BDG_LIST
is always used with the
.Dv NIOCGINFO
command of
.Xr ioctl 2 .
.Pp
Below is an example of printing all the existing ports walking through
all the bridges.
.Bd -literal
struct nmreq nmr;
int fd = open("/dev/netmap", O_RDWR);

bzero(&nmr, sizeof(nmr));
nmr.nr_version = NETMAP_API;
nmr.nr_cmd = NETMAP_BDG_LIST;
nmr.nr_arg1 = nmr.nr_arg2 = 0; /* start from bridge:0 port:0 */
for (; !ioctl(fd, NIOCGINFO, &nmr); nmr.nr_arg2++) {
	D("bridge:%d port:%d %s", nmr.nr_arg1, nmr.nr_arg2,
	    nmr.nr_name);
	nmr.nr_name[0] = '\\0';
}
.Ed
.Ss LIMITS
.Nm
currently supports up to 8 switches, 254 ports per switch,
1024 buffers per port.
These hard limits will be changed to
.Xr sysctl 8
variables in future releases.
.Pp
Attaching the host stack to the bridge imposes significant performance
degradation when many packets are forwarded to the host stack.
This is because each packet forwarded to the host stack causes
.Xr mbuf 9
allocation in the same thread context.
.Sh SYSCTL VARIABLES
.Nm
uses the following
.Xr sysctl 8
variables to control operation:
.Bl -tag -width "dev.netmap.verbose"
.It dev.netmap.bridge
The maximum number of packets processed internally
in each iteration.
Defaults to 1024, use lower values to trade latency
with throughput.
.It dev.netmap.verbose
Set to non-zero values to enable in-kernel diagnostics.
.El
.Sh EXAMPLES
Create one switch, with a traffic generator connected to one
port, and a
.Xr netmap 4 Ns -enabled
.Xr tcpdump 1
instance on another port:
.Bd -literal -offset indent
tcpdump -ni vale-a:1 &
pkt-gen  -i vale-a:0 -f tx &
.Ed
.Pp
Create two switches,
each connected to two qemu machines on different ports.
.Bd -literal -offset indent
qemu -net nic -net netmap,ifname=vale-1:a ... &
qemu -net nic -net netmap,ifname=vale-1:b ... &
qemu -net nic -net netmap,ifname=vale-2:c ... &
qemu -net nic -net netmap,ifname=vale-2:d ... &
.Ed
.Sh SEE ALSO
.Xr netmap 4
.Rs
.%A Luigi Rizzo
.%A Giuseppe Lettieri
.%T VALE, a switched ethernet for virtual machines
.%J http://info.iet.unipi.it/~luigi/vale/
.%D June 2012
.Re
.Sh AUTHORS
.An -nosplit
The
.Nm
switch has been designed and implemented in 2012 by
.An Luigi Rizzo
and
.An Giuseppe Lettieri
at the Universita` di Pisa.
.Pp
.Nm
has been funded by the European Commission within the FP7 Projects
CHANGE (257422) and OPENLAB (287581).