Phonet: improve documentation
Fix grammar errors spotted by Randy Dunlap, and adds some more details. Signed-off-by: Remi Denis-Courmont <remi.denis-courmont@nokia.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -21,7 +21,7 @@ depending on the device, such as:
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Packets format
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--------------
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Phonet packet have a common header as follow:
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Phonet packets have a common header as follows:
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struct phonethdr {
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uint8_t pn_media; /* Media type (link-layer identifier) */
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@ -33,14 +33,17 @@ Phonet packet have a common header as follow:
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uint8_t pn_sobj; /* Sender object ID */
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};
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The device ID is split: the 6 higher order bits consitutes the device
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address, while the 2 lower order bits are used for multiplexing, as are
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the 8-bits object identifiers. As such, Phonet can be considered as a
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On Linux, the link-layer header includes the pn_media byte (see below).
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The next 7 bytes are part of the network-layer header.
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The device ID is split: the 6 higher-order bits consitute the device
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address, while the 2 lower-order bits are used for multiplexing, as are
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the 8-bit object identifiers. As such, Phonet can be considered as a
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network layer with 6 bits of address space and 10 bits for transport
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protocol (much like port numbers in IP world).
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The modem always has address number zero. Each other device has a its
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own 6-bits address.
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The modem always has address number zero. All other device have a their
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own 6-bit address.
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Link layer
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@ -49,11 +52,18 @@ Link layer
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Phonet links are always point-to-point links. The link layer header
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consists of a single Phonet media type byte. It uniquely identifies the
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link through which the packet is transmitted, from the modem's
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perspective.
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perspective. Each Phonet network device shall prepend and set the media
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type byte as appropriate. For convenience, a common phonet_header_ops
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link-layer header operations structure is provided. It sets the
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media type according to the network device hardware address.
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Linux Phonet network interfaces use a dedicated link layer type
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(ETH_P_PHONET) which is out of the Ethernet type range. They can only
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send and receive Phonet packets.
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Linux Phonet network interfaces support a dedicated link layer packets
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type (ETH_P_PHONET) which is out of the Ethernet type range. They can
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only send and receive Phonet packets.
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The virtual TUN tunnel device driver can also be used for Phonet. This
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requires IFF_TUN mode, _without_ the IFF_NO_PI flag. In this case,
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there is no link-layer header, so there is no Phonet media type byte.
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Note that Phonet interfaces are not allowed to re-order packets, so
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only the (default) Linux FIFO qdisc should be used with them.
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