socket (9)

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 Copyright (c) 2006 Robert N. M. Watson
 Copyright (c) 2014 Benjamin J. Kaduk
 All rights reserved.

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 1. Redistributions of source code must retain the above copyright
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(The comments found at the beginning of the groff file "man9/socket.9freebsd".)

NAME

socket - kernel socket interface

SYNOPSIS

In sys/socket.h In sys/socketvar.h Ft int Fn sobind struct socket *so struct sockaddr *nam struct thread *td Ft void Fn soclose struct socket *so Ft int Fn soconnect struct socket *so struct sockaddr *nam struct thread *td Ft int Fo socreate Fa int dom struct socket **aso int type int proto Fa struct ucred *cred struct thread *td Fc Ft int Fn sogetopt struct socket *so struct sockopt *sopt Ft int Fo soreceive Fa struct socket *so struct sockaddr **psa struct uio *uio Fa struct mbuf **mp0 struct mbuf **controlp int *flagsp Fc Ft int Fn sosetopt struct socket *so struct sockopt *sopt Ft int Fo sosend Fa struct socket *so struct sockaddr *addr struct uio *uio Fa struct mbuf *top struct mbuf *control int flags struct thread *td Fc Ft int Fn soshutdown struct socket *so int how

DESCRIPTION

The kernel ifconfig programming interface permits in-kernel consumers to interact with local and network socket objects in a manner similar to that permitted using the socket(2) user API. These interfaces are appropriate for use by distributed file systems and other network-aware kernel services. While the user API operates on file descriptors, the kernel interfaces operate directly on Vt struct socket pointers.

Except where otherwise indicated, ifconfig functions may sleep, and are not appropriate for use in an ithread(9) context or while holding non-sleepable kernel locks.

Creating and Destroying Sockets

A new socket may be created using Fn socreate . As with socket(2), arguments specify the requested domain, type, and protocol via Fa dom , type , and Fa proto . The socket is returned via Fa aso on success. In addition, the credential used to authorize operations associated with the socket will be passed via Fa cred (and will be cached for the lifetime of the socket), and the thread performing the operation via Fa td . Warning authorization of the socket creation operation will be performed using the thread credential for some protocols (such as raw sockets).

Sockets may be closed and freed using Fn soclose , which has similar semantics to close(2).

Connections and Addresses

The Fn sobind function is equivalent to the bind(2) system call, and binds the socket Fa so to the address Fa nam . The operation would be authorized using the credential on thread Fa td .

The Fn soconnect function is equivalent to the connect(2) system call, and initiates a connection on the socket Fa so to the address Fa nam . The operation will be authorized using the credential on thread Fa td . Unlike the user system call, Fn soconnect returns immediately; the caller may msleep(9) on Fa so->so_timeo while holding the socket mutex and waiting for the SS_ISCONNECTING flag to clear or Fa so->so_error to become non-zero. If Fn soconnect fails, the caller must manually clear the SS_ISCONNECTING flag.

The Fn soshutdown function is equivalent to the shutdown(2) system call, and causes part or all of a connection on a socket to be closed down.

Socket Options

The Fn sogetopt function is equivalent to the getsockopt(2) system call, and retrieves a socket option on socket Fa so . The Fn sosetopt function is equivalent to the setsockopt(2) system call, and sets a socket option on socket Fa so .

The second argument in both Fn sogetopt and Fn sosetopt is the Fa sopt pointer to a Vt struct sopt describing the socket option operation. The caller-allocated structure must be zeroed, and then have its fields initialized to specify socket option operation arguments:

sopt_dir

Set to SOPT_SET or SOPT_GET depending on whether this is a get or set operation.

sopt_level

Specify the level in the network stack the operation is targeted at; for example, SOL_SOCKET

sopt_name

Specify the name of the socket option to set.

sopt_val

Kernel space pointer to the argument value for the socket option.

sopt_valsize

Size of the argument value in bytes.

Socket I/O

The Fn soreceive function is equivalent to the recvmsg(2) system call, and attempts to receive bytes of data from the socket Fa so , optionally blocking awaiting for data if none is ready to read. Data may be retrieved directly to kernel or user memory via the Fa uio argument, or as an mbuf chain returned to the caller via Fa mp0 , avoiding a data copy. The Fa uio must always be non- NULL If Fa mp0 is non- NULL only the uio_resid of Fa uio is used. The caller may optionally retrieve a socket address on a protocol with the PR_ADDR capability by providing storage via non- NULL Fa psa argument. The caller may optionally retrieve control data mbufs via a non- NULL Fa controlp argument. Optional flags may be passed to Fn soreceive via a non- NULL Fa flagsp argument, and use the same flag name space as the recvmsg(2) system call.

The Fn sosend function is equivalent to the sendmsg(2) system call, and attempts to send bytes of data via the socket Fa so , optionally blocking if data cannot be immediately sent. Data may be sent directly from kernel or user memory via the Fa uio argument, or as an mbuf chain via Fa top , avoiding a data copy. Only one of the Fa uio or Fa top pointers may be non- NULL An optional destination address may be specified via a non- NULL Fa addr argument, which may result in an implicit connect if supported by the protocol. The caller may optionally send control data mbufs via a non- NULL Fa control argument. Flags may be passed to Fn sosend using the Fa flags argument, and use the same flag name space as the sendmsg(2) system call.

Kernel callers running in ithread(9) context, or with a mutex held, will wish to use non-blocking sockets and pass the MSG_DONTWAIT flag in order to prevent these functions from sleeping.

SEE ALSO

bind(2), close(2), connect(2), getsockopt(2), recv(2), send(2), setsockopt(2), shutdown(2), socket(2), ng_ksocket4, ithread(9), msleep(9), ucred(9)

HISTORY

The socket(2) system call appeared in BSD 4.2 This manual page was introduced in Fx 7.0 .

AUTHORS

This manual page was written by An Robert Watson .

BUGS

The use of explicitly passed credentials, credentials hung from explicitly passed threads, the credential on curthread and the cached credential from socket creation time is inconsistent, and may lead to unexpected behaviour. It is possible that several of the Fa td arguments should be Fa cred arguments, or simply not be present at all.

The caller may need to manually clear SS_ISCONNECTING if Fn soconnect returns an error.

The MSG_DONTWAIT flag is not implemented for Fn sosend , and may not always work with Fn soreceive when zero copy sockets are enabled.

This manual page does not describe how to register socket upcalls or monitor a socket for readability/writability without using blocking I/O.

The Fn soref and Fn sorele functions are not described, and in most cases should not be used, due to confusing and potentially incorrect interactions when Fn sorele is last called after Fn soclose .