This change adds all the kernel parts of a network stack. The network stack is partial but implements many of the important parts. Add if(4) network interface abstraction. Network interfaces are registered in a global list that can be iterated and each assigned an unique integer identifier. Add reference counted packets with a cache that recycles recent packets. Add support for lo(4) loopback and ether(4) ethernet network interfaces. The /dev/lo0 loopback device is created automatically on boot. Add arp(4) address resolution protocol driver for translation of inet(4) network layer addresses into ether(4) link layer addresses. arp(4) entries are cached and evicted from the cache when needed or when the entry has not been used for a while. The cache is limited to 256 entries for now. Add ip(4) internet protocol version 4 support. IP fragmentation and options are not implemented yet. Add tcp(4) transmission control protocol sockets for a reliable transport layer protocol that provides a reliable byte stream connection between two hosts. The implementation is incomplete and does not yet implement out of band data, options, and high performance extensions. Add udp(4) user datagram protocol sockets for a connectionless transport layer that provides best-effort delivery of datagrams. Add ping(4) sockets for a best-effort delivery of echo datagrams. Change type of sa_family_t from unsigned short to uint16_t. Add --disable-network-drivers to the kernel(7) options and expose it with a bootloader menu. tix-iso-bootconfig can set this option by default. Import CRC32 code from libz for the Ethernet checksum. This is a compatible ABI change that adds features to socket(2) (AF_INET, IPPROTO_TCP, IPPROTO_UDP, IPPROTO_PING), the ioctls for if(4), socket options, and the lo0 loopback interface. This commit is based on work by Meisaka Yukara contributed as the commit bbf7f1e8a5238a2bd1fe8eb1d2cc5c9c2421e2c4. Almost no lines of this work remains in this final commit as it has been rewritten or refactored away over the years, see the individual file headers for which files contain remnants of this work. Co-authored-by: Meisaka Yukara <Meisaka.Yukara@gmail.com>
538 lines
16 KiB
Groff
538 lines
16 KiB
Groff
.Dd June 4, 2017
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.Dt PING 4
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.Os
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.Sh NAME
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.Nm ping
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.Nd ping protocol
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.Sh SYNOPSIS
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.In sys/socket.h
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.In netinet/in.h
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.In netinet/ping.h
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.Ft int
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.Fn socket AF_INET SOCK_DGRAM IPPROTO_PING
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.Sh DESCRIPTION
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The Ping Protocol uses the Echo Request and Echo Reply messages of the Internet
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Control Message Protocol (ICMP) to provide a connectionless best-effort echo of
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datagrams.
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A cooperating host will send back a Echo Reply message containing the same data
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as any Echo Request messages it receives.
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It is designed for packet-switched networks and provides multiplexing with a
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16-bit port number (using the identifier field of the Echo Request and Echo
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Reply messages), and basic data integrity checks (16-bit ones' complement sum),
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and broadcasting.
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It does not provide a guarantee of delivery, avoidance of delivering multiple
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times, ordering, out of band data, nor flow control.
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.Pp
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Ping sockets allow only sending Echo Request messages and receiving Echo Reply
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messages.
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The kernel will automatically send Echo Reply messages in response to any
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received Echo Request Messages.
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.Pp
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The structure of ping datagrams is a 4 bytes sequence number (in big endian)
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followed by 0 or more bytes of an optional payload.
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Ping datagrams are sent inside a Echo Request message (with that sequence
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number) and received inside a Echo Reply message (also containing a sequence
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number).
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.Pp
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Ping sockets are made with
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.Xr socket 2
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by passing an appropriate
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.Fa domain
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.Dv ( AF_INET ) ,
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.Dv SOCK_DGRAM
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as the
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.Fa type ,
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and
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.Dv IPPROTO_PING
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as the
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.Fa protocol .
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Initially a socket is not bound, it won't receive datagrams, and it does not
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have a remote address and port set.
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.Pp
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A Ping socket has the following state:
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.Pp
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.Bl -bullet -compact
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.It
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The address family it belongs to.
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.It
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The network interface it is bound to (if any)
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.Dv ( SO_BINDTODEVICE
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and
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.Dv SO_BINDTOINDEX )
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(initially none).
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.It
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The local address and port (when bound) (initially none).
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.It
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The remote address and port (when connected) (initially none).
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.It
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A receive queue (initially empty).
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.It
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Whether the socket has been
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.Xr shutdown 2
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for read and/or write (initially neither).
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.It
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A single pending asynchronous error (if any)
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.Dv ( SO_ERROR )
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(initially none).
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.It
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Whether broadcast datagrams can be sent
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.Dv ( SO_BROADCAST )
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(initially no).
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.It
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Whether binding to the any address and a port doesn't conflict with binding to
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another address on the same port
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.Dv ( SO_REUSEADDR )
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(initially no).
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.It
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Limits on the size of the receive and send queues
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.Dv ( SO_RCVBUF
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and
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.Dv SO_SNDBUF ) .
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.El
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.Pp
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Datagrams are sent as a packet with a header and the datagram itself.
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The header contains the port and the checksum.
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The header is 8 bytes.
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.Pp
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Port numbers are 16-bit and range from 1 to 65535.
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Port 0 is not valid.
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Binding to port 0 will assign an available port on the requested address.
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Sending or connecting to port 0 will fail with
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.Er EADDRNOTAVAIL .
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Received Echo Reply packets whose port number is port 0 will be silently
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dropped.
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Ping ports are distinct from ports in other transport layer protocols.
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.Pp
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Packets contain a 16-bit ones' complement checksum.
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A received packet will be silently discarded if its checksum does not match its
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contents.
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.Pp
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Sockets can be bound to a local address and port with
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.Xr bind 2
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(if not already bound),
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or an local address and port will be automatically assigned on the first send
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or connect operation.
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The local address and port can be read with
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.Xr getsockname 2 .
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If the socket hasn't been bound, the local address and port is reported as the
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any address on port 0.
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There are no ports that require superuser privileges.
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.Pp
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Sockets can be bound to the any address, the broadcast address, the address of
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a network interface, or the broadcast address of a network interface.
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Binding to port 0 will automatically assign an available port on the requested
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local address or fail with
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.Er EAGAIN
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if no port is available.
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No two sockets can bind to the same local address and port.
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No two sockets can be bound such that one is bound to the any address and a
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port, and the other socket is bound to another address and the same port; unless
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both sockets had the
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.Dv SO_REUSEADDR
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socket option set when the second socket was bound, and the current user is the
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same that bound the first socket or the current user has superuser privileges.
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.Pp
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A socket bound to a local address and port will receive an incoming datagram of
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the following conditions hold:
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.Pp
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.Bl -bullet -compact
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.It
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The datagram belongs to the socket's address family and the protocol is Ping.
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.It
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The datagram's checksum matches the datagram.
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.It
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The datagram is an Echo Reply message.
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.It
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The datagram's port number is not port 0.
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.It
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The datagram is sent to the address or broadcast address of the network
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interface it is received on, or the datagram was sent to the broadcast address;
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.It
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The socket is either bound to the receiving network interface, or the socket is
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not bound to a network interface;
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.It
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The datagram is sent to the socket's local port;
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.It
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The datagram is sent to the socket's local address, or the socket's local
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address is the any address (and no other socket is bound to the datagram's
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address and that port);
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.It
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The socket is connected and the datagram was sent from the remote address and
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the remote port, or the socket is not connected; and
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.It
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The socket is not shut down for reading.
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.El
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.Pp
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If so, the datagram is added to the socket's receive queue, otherwise it is
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discarded.
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The receive queue contains incoming packets waiting to be received.
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Incoming packets are dropped if the receive queue is full.
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Shrinking the receive queue limit drops packets as needed to stay below the
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limit.
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.Pp
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The remote address and port can be set multiple times with
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.Xr connect 2 ,
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after which the socket is said to be connected, but Ping is connectionless and
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no handshake is sent.
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The remote port must not be port 0 or the connection will fail with
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.Er EADDRNOTAVAIL .
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If the socket is not bound,
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.Xr connect 2
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will determine which network interface will be used to send to the remote
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address, and then bind to the address of that network interface together with an
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available port.
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.Xr connect 2
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will fail if there is no route from the local address to the requested remote
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address.
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A connected socket only receive datagrams from the remote address and port.
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.Xr connect 2
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will drop datagrams in the receive queue that don't originate from the
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requested remote address.
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The
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.Xr send 2 ,
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.Xr write 2 ,
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and
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.Xr writev 2
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functions can be used on a connected socket and they send to the remote address
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and port by default.
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If the socket is connected, the destination given to
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.Xr sendto 2
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and
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.Xr sendmsg 2
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must be
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.Dv NULL .
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The remote address and port can be read with
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.Xr getpeername 2 .
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.Pp
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The socket can be disconnected by connecting to a socket address with the family
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value set to
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.Dv AF_UNSPEC ,
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which resets the remote address and port (if set), and otherwise has no effect.
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.Pp
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Datagrams can be sent with
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.Xr sendmsg 2
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and
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.Xr sendto 2 .
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Sending on a socket not bound to a local address and port will bind to the
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any address and an available port, or fail with
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.Er EAGAIN
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if no port is available.
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Datagrams can be received with
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.Xr recvmsg 2 ,
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.Xr recvfrom 2 ,
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.Xr recv 2 ,
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.Xr read 2 ,
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and
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.Xr readv 2 .
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If an asynchronous error is pending, the next send and receive operation will
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fail with that error and clear the asynchronous eror, so the next operation can
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succeed.
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Asynchronous errors can arise from network problems.
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There is no send queue at the Ping level and datagrams are directly forwarded to
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the network layer.
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It is an error to use any of the flags
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.Dv MSG_CMSG_CLOEXEC ,
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.Dv MSG_CMSG_CLOFORK ,
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.Dv MSG_EOR ,
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.Dv MSG_OOB ,
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and
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.Dv MSG_WAITALL .
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.Pp
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The condition of the socket can be tested with
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.Xr poll 2
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where
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.Dv POLLIN
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signifies a packet has been received (or the socket is shut down for reading),
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.Dv POLLOUT
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signifies a packet can be sent now (and the socket is not shut down for
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writing),
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.Dv POLLHUP
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signifies the socket is shut down for writing, and
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.Dv POLLERR
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signifies an asynchronous error is pending.
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.Pp
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The socket can be shut down for receiving and/or sending with
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.Xr shutdown 2 .
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The receive queue is emptied when shut down for receive (asynchronous errors are
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preserved) and receive operations will succeed with an end of file
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condition, but any pending asynchronous errors will take precedence and be
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delivered instead.
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Sending when shut down for writing will raise
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.Dv SIGPIPE
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and fail with
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.Er EPIPE
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(regardless of a pending asynchronous error).
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.Pp
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Socket options can be set with
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.Xr setsockopt 2
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and read with
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.Xr getsockopt 2
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and exist on the
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.Dv IPPROTO_PING
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level as well as applicable underlying protocol levels.
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.Pp
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Broadcast Echo Requests can be sent by setting the
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.Dv SO_BROADCAST
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socket option with
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.Xr setsockopt 2
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and sending to a broadcast address of the network layer.
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RFC 1122 3.2.2.6 allows hosts to ignore broadcast Echo Requests.
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.Sh SOCKET OPTIONS
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Ping sockets support these
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.Xr setsockopt 2 /
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.Xr getsockopt 2
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options at level
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.Dv SOL_SOCKET :
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.Bl -tag -width "12345678"
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.It Dv SO_BINDTODEVICE Fa "char[]"
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Bind to a network interface by its name.
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(Described in
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.Xr if 4 )
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.It Dv SO_BINDTOINDEX Fa "unsigned int"
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Bind to a network interface by its index number.
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(Described in
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.Xr if 4 )
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.It Dv SO_BROADCAST Fa "int"
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Whether sending to a broadcast address is allowed.
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(Described in
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.Xr if 4 )
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.It Dv SO_DEBUG Fa "int"
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Whether the socket is in debug mode.
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This option is not implemented and is initially 0.
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Attempting to set it to non-zero will fail with
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.Er EPERM .
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(Described in
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.Xr if 4 )
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.It Dv SO_DOMAIN Fa "sa_family_t"
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The socket
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.Fa domain
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(the address family).
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This option can only be read.
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(Described in
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.Xr if 4 )
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.It Dv SO_DONTROUTE Fa "int"
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Whether to bypass the routing table and only send on the local network.
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This option is not implemented and is initially 0.
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Attempting to set it to non-zero will fail with
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.Er EPERM .
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(Described in
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.Xr if 4 )
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.It Dv SO_ERROR Fa "int"
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The asynchronous pending error
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(an
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.Xr errno 3
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value).
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Cleared to 0 when read.
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This option can only be read.
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(Described in
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.Xr if 4 )
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.It Dv SO_PROTOCOL Fa "int"
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The socket protocol
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.Dv ( IPPROTO_PING ) .
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This option can only be read.
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(Described in
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.Xr if 4 )
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.It Dv SO_RCVBUF Fa "int"
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How many bytes the receive queue can use (default is 64 pages, max 4096 pages).
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(Described in
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.Xr if 4 )
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.It Dv SO_REUSEADDR Fa "int"
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Whether binding to the any address on a port doesn't conflict with binding to
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another address and the same port, if both sockets have this option set and the
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user binding the second socket is the same that bound the first socket or the
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user binding the second socket has superuser privileges.
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(Described in
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.Xr if 4 )
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.It Dv SO_SNDBUF Fa "int"
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How many bytes the send queue can use (default is 64 pages, max 4096 pages).
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(Described in
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.Xr if 4 )
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.It Dv SO_TYPE Fa "int"
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The socket type
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.Dv ( SOCK_DGRAM ) .
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This option can only be read.
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(Described in
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.Xr if 4 )
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.El
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.Sh IMPLEMENTATION NOTES
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Received broadcast echo requests are ignored as permitted by RFC 1122 3.2.2.6.
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.Pp
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Each packet currently use a page of memory, which counts towards the receive
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queue limit.
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.Pp
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If no specific port is requested, one is randomly selected in the dynamic port
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range 32768 (inclusive) through 61000 (exclusive).
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.Sh EXAMPLES
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This example sends a Echo Request and blocks indefinitely until it receives a
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Echo Reply.
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.Va remote
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is the remote socket address and
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.Va remote_len
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is the size of
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.Va remote.
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The
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.Va remote
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and
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.Va remote_len
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values should all be chosen according to the address family and network layer.
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.Bd -literal
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sa_family_t af = /* ... */;
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const struct sockaddr *remote = /* ... */;
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socklen_t remote_len = /* ... */;
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int fd = socket(af, SOCK_DGRAM, IPPROTO_PING);
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if (fd < 0)
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err(1, "socket");
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if (connect(fd, remote, remote_len) < 0)
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err(1, "connect");
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unsigned char request[56];
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arc4random_buf(request, sizeof(request));
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if (send(fd, request, sizeof(request), 0) < 0)
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err(1, "send");
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unsigned char reply[56 + 1 /* detect too large reply */];
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ssize_t amount = recv(fd, reply, sizeof(reply), 0);
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if (amount < 0 )
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err(1, "recv");
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if (amount == sizeof(request) && !memcmp(request, reply, sizeof(request)))
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printf("correct echo reply\\n");
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else
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printf("incorrect echo reply\\n");
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.Ed
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.Sh ERRORS
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Socket operations can fail due to these error conditions, in addition to the
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error conditions of the network and link layer, and the error conditions of the
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invoked function.
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.Bl -tag -width [EADDRNOTAVAIL]
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.It Bq Er EACCES
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A datagram was sent to a broadcast address, but
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.Dv SO_BROADCAST
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is turned off.
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.It Bq Er EADDRINUSE
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The socket cannot be bound to the requested address and port because another
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socket was already bound to 1) the same address and port 2) the any address
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and the same port (and
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.Dv SO_REUSEADDR
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was not set on both sockets), or 3) some address and the same port but the
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requested address was the any address (and
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.Dv SO_REUSEADDR
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was not set on both sockets).
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.It Bq Er EADDRNOTAVAIL
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The socket cannot be bound to the requested address because no network interface
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had that address or broadcast address.
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.It Bq Er EAGAIN
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A port could not be assigned because each port in the dynamic port range had
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already been bound to a socket in a conflicting manner.
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.It Bq Er ECONNREFUSED
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The destination host of a datagram was not listening on the port.
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This error can happen asynchronously.
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.It Bq Er EHOSTDOWN
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The destination host of a datagram is not up.
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This error can happen asynchronously.
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.It Bq Er EHOSTUNREACH
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The destination host of a datagram was unreachable.
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This error can happen asynchronously.
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.It Bq Er EISCONN
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A destination address and port was specified when sending a datagram, but the
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socket has already been connected to a remote address and port.
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.It Bq Er EMSGSIZE
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The datagram was too large to be sent because it exceeded the maximum
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transmission unit (MTU) on the path between the local and remote address.
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This error can happen asynchronously.
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.It Bq Er ENETDOWN
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The network interface used to deliver a datagram isn't up.
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This error can happen asynchronously.
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.It Bq Er ENETUNREACH
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The destination network of a datagram was unreachable.
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This error can happen asynchronously.
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.It Bq Er ENETUNREACH
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The remote address could not be connected because there was no route from the
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local address to the remote address.
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.It Bq Er ENOBUFS
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There was not enough memory available for network packets.
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.It Bq Er EPERM
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One of the unimplemented
|
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.Dv SO_DEBUG
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and
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.Dv SO_DONTROUTE
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socket options was attempted to be set to a non-zero value.
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.El
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|
.Sh SEE ALSO
|
|
.Xr bind 2 ,
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|
.Xr connect 2 ,
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.Xr getpeername 2 ,
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|
.Xr getsockname 2 ,
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.Xr getsockopt 2 ,
|
|
.Xr poll 2 ,
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.Xr recvfrom 2 ,
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.Xr recvmsg 2 ,
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.Xr sendmsg 2 ,
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.Xr sendto 2 ,
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.Xr setsockopt 2 ,
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.Xr shutdown 2 ,
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.Xr socket 2 ,
|
|
.Xr icmp 4 ,
|
|
.Xr if 4 ,
|
|
.Xr inet 4 ,
|
|
.Xr ip 4 ,
|
|
.Xr kernel 7
|
|
.Sh STANDARDS
|
|
.Rs
|
|
.%A J. Postel (ed.)
|
|
.%D September 1981
|
|
.%R STD 5
|
|
.%R RFC 792
|
|
.%T Internet Control Message Protocol - DARPA Internet Program Protocol Specification
|
|
.%Q USC/Information Sciences Institute
|
|
.Re
|
|
.Pp
|
|
.Rs
|
|
.%A Internet Engineering Task Force
|
|
.%A R. Braden (ed.)
|
|
.%D October 1989
|
|
.%R STD 3
|
|
.%R RFC 1122
|
|
.%T Requirements for Internet Hosts -- Communication Layers
|
|
.%Q USC/Information Sciences Institute
|
|
.Re
|
|
.Sh HISTORY
|
|
Ping sockets originally appeared in Sortix 1.1.
|
|
.Sh BUGS
|
|
The handling of
|
|
.Dv SO_REUSEADDR in
|
|
.Xr bind 2
|
|
does not yet enforce the two sockets to be bound by the same user or the second
|
|
socket to be bound by a user with superuser privileges.
|
|
The requirement that both sockets have
|
|
.Dv SO_REUSEADDR
|
|
set might be relaxed to only the second socket having it set when this
|
|
permission check is implemented.
|
|
.Pp
|
|
The integration with the network layer is inadequate and the asynchronous errors
|
|
.Er ECONNREFUSED ,
|
|
.Er EHOSTDOWN ,
|
|
.Er EHOSTUNREACH ,
|
|
and
|
|
.Er ENETUNREACH
|
|
are never delivered asynchronously from the network.
|
|
.Pp
|
|
Ping sockets does not yet provide access to IP header values such as the Time
|
|
To Live and does not yet report ICMP error messages.
|
|
.Pp
|
|
The
|
|
.Xr send 2
|
|
flag
|
|
.Dv MSG_DONTROUTE
|
|
and the
|
|
.Dv SO_DONTROUTE
|
|
socket option are not implemented yet.
|
|
.Pp
|
|
The
|
|
.Dv SO_SNDBUF
|
|
socket option is currently not used and the send queue is not limited at the
|
|
socket level.
|
|
.Pp
|
|
The automatic assignment of ports is random, but is statistically biased.
|
|
A random port is picked, and if it is taken, the search sequentially iterates
|
|
ports in ascending order until an available port is found or the search
|
|
terminates.
|