Commit 95430c0b authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont Committed by David S. Miller

Phonet: pipe end-point protocol documentation

Signed-off-by: default avatarRémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 02a47617
......@@ -112,6 +112,60 @@ However, connect() and getpeername() are not supported, as they did
not seem useful with Phonet usages (could be added easily).
Phonet Pipe protocol
--------------------
The Phonet Pipe protocol is a simple sequenced packets protocol
with end-to-end congestion control. It uses the passive listening
socket paradigm. The listening socket is bound to an unique free object
ID. Each listening socket can handle up to 255 simultaneous
connections, one per accept()'d socket.
int lfd, cfd;
lfd = socket(PF_PHONET, SOCK_SEQPACKET, PN_PROTO_PIPE);
listen (lfd, INT_MAX);
/* ... */
cfd = accept(lfd, NULL, NULL);
for (;;)
{
char buf[...];
ssize_t len = read(cfd, buf, sizeof(buf));
/* ... */
write(cfd, msg, msglen);
}
Connections are established between two endpoints by a "third party"
application. This means that both endpoints are passive; so connect()
is not possible.
WARNING:
When polling a connected pipe socket for writability, there is an
intrinsic race condition whereby writability might be lost between the
polling and the writing system calls. In this case, the socket will
block until write because possible again, unless non-blocking mode
becomes enabled.
The pipe protocol provides two socket options at the SOL_PNPIPE level:
PNPIPE_ENCAP accepts one integer value (int) of:
PNPIPE_ENCAP_NONE: The socket operates normally (default).
PNPIPE_ENCAP_IP: The socket is used as a backend for a virtual IP
interface. This requires CAP_NET_ADMIN capability. GPRS data
support on Nokia modems can use this. Note that the socket cannot
be reliably poll()'d or read() from while in this mode.
PNPIPE_IFINDEX is a read-only integer value. It contains the
interface index of the network interface created by PNPIPE_ENCAP,
or zero if encapsulation is off.
Authors
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