SHMIF(4)

SHMIF(4) | Device Drivers Manual | SHMIF(4)

# NAME

`shmif` — rump kernel shared memory network interface

# SYNOPSIS

`#include <rump/rump.h>`

int
`rump_pub_shmif_create`(const char *path, int *ifnum);

# DESCRIPTION

The `shmif` interface uses a memory mapped regular file as a virtual Ethernet bus. All interfaces connected to the same bus see each others' traffic.

Using a memory mapped regular file as a bus has two implications:

1. The bus identifier is not in flat global namespace.
2. Configuring and using the interface is possible without superuser privileges on the host (normal host file access permissions for the bus hold).

It is not possible to directly access the host networking facilities from a rump kernel using purely `shmif`. However, traffic can be routed to another rump kernel instance which provides both `shmif` and virt(4) networking.

An `shmif` interface can be created in two ways:

- Programmatically by calling `rump_pub_shmif_create`(). The bus pathname is passed in path. The number of the newly created interface is available after a successful call by dereferencing ifnum.
- Dynamically at runtime with ifconfig(8) or equivalent using the create command. In this case the bus path must be configured with ifconfig(8) linkstr before the interface address can be configured.

Destroying an `shmif` interface is possible only via ifconfig(8) destroy.

An `shmif` interface emulates TX/RX offload options in software. They are specified by ifconfig(8). Alternatively, its if_capenable flag is directly specified by environment variable `RUMP_SHMIF_CAPENABLE`, for example:

0x7ff80
  for all TX/RX offload
0x6aa80
  for all TX offload
0x15500
  for all RX offload

See /usr/include/net/if.h for more details.

# SEE ALSO

rump(3), virt(4), ifconfig(8)

December 12, 2018 | NetBSD 11.0