usb虚拟网卡
1. USB Gadget functions configurable through configfs
1.1. RNDIS
Microsoft Windows XP bundles the "Remote NDIS" (RNDIS) protocol,
and Microsoft provides redistributable binary RNDIS drivers for
older versions of Windows.
To make MS-Windows work with this, use Documentation/usb/linux.inf
as the "driver info file". For versions of MS-Windows older than
XP, you'll need to download drivers from Microsoft's website; a URL
is given in comments found in that info file.
1.2. CDC ECM
The "Communication Device Class" (CDC) Ethernet Control Model.
That protocol is often avoided with pure Ethernet adapters, in
favor of simpler vendor-specific hardware, but is widely
supported by firmware for smart network devices
1.3. CDC ECM subset
On hardware that can't implement the full protocol,
a simple CDC subset is used, placing fewer demands on USB.
1.4. CDC NCM
NCM is an advanced protocol for Ethernet encapsulation, allows
grouping of several ethernet frames into one USB transfer and
different alignment possibilities.
1.5. EEM
CDC EEM is a newer USB standard that is somewhat simpler than CDC ECM
and therefore can be supported by more hardware. Technically ECM and
EEM are designed for different applications. The ECM model extends
the network interface to the target (e.g. a USB cable modem), and the
EEM model is for mobile devices to communicate with hosts using
ethernet over USB. For Linux gadgets, however, the interface with
the host is the same (a usbX device), so the differences are minimal
2. USB Gadget precomposed configurations
2.1. NCM
This driver implements USB CDC NCM subclass standard. NCM is
an advanced protocol for Ethernet encapsulation, allows grouping
of several ethernet frames into one USB transfer and different
alignment possibilities.
2.2. Ethernet Gadget
This driver implements Ethernet style communication, in one of
several ways:
- The "Communication Device Class" (CDC) Ethernet Control Model.
That protocol is often avoided with pure Ethernet adapters, in
favor of simpler vendor-specific hardware, but is widely
supported by firmware for smart network devices.
- On hardware can't implement that protocol, a simple CDC subset
is used, placing fewer demands on USB.
- CDC Ethernet Emulation Model (EEM) is a newer standard that has
a simpler interface that can be used by more USB hardware.
RNDIS support is an additional option, more demanding than subset.
Within the USB device, this gadget driver exposes a network device
"usbX", where X depends on what other networking devices you have.
Treat it like a two-node Ethernet link: host, and gadget.
The Linux-USB host-side "usbnet" driver interoperates with this
driver, so that deep I/O queues can be supported. On 2.4 kernels,
use "CDCEther" instead, if you're using the CDC option. That CDC
mode should also interoperate with standard CDC Ethernet class
drivers on other host operating systems.
