lib/libc/sys/close.2 - master - nerfur/openbsd-src

lib/libc/sys/close.2
133 строки4 KB
deraadt
delete an ancient paragraph suggesting the wrong reason to use close(2)
15 апр 2022, 06:04
15 апр 2022, 06:04f0263d4
.\"	$OpenBSD: close.2,v 1.19 2022/04/15 03:04:52 deraadt Exp $
.\"	$NetBSD: close.2,v 1.5 1995/02/27 12:32:14 cgd Exp $
.\"
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.\"     @(#)close.2	8.2 (Berkeley) 4/19/94
.\"
.Dd $Mdocdate: April 15 2022 $
.Dt CLOSE 2
.Os
.Sh NAME
.Nm close
.Nd delete a descriptor
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn close "int d"
.Sh DESCRIPTION
The
.Fn close
call deletes a descriptor
.Fa d
from the per-process object
reference table.
If this is the last reference to the underlying object, the
object will be deactivated.
For example, on the last close of a file,
the current
.Em seek
pointer associated with the file is lost;
on the last close of a
.Xr socket 2 ,
associated naming information and queued data are discarded;
and on the last close of a file holding an advisory lock,
the lock is released (see
.Xr flock 2 ) .
However, the semantics of System V and
.St -p1003.1-88
dictate that all
.Xr fcntl 2
advisory record locks associated with a file for a given process
are removed when
.Em any
file descriptor for that file is closed by that process.
.Pp
When a process forks (see
.Xr fork 2 ) ,
all descriptors for the new child process reference the same
objects as they did in the parent before the fork.
If a new process image is to then be run using
.Xr execve 2 ,
the process would normally inherit these descriptors.
Most of the descriptors can be rearranged with
.Xr dup2 2
or deleted with
.Fn close
before the
.Xr execve 2
is attempted, but since some of these descriptors may still
be needed should the
.Xr execve 2
fail, it is necessary to arrange for them
to be closed when the
.Xr execve 2
succeeds.
For this reason, the call
.Fn fcntl d F_SETFD FD_CLOEXEC
is provided,
which arranges that a descriptor will be closed after a successful
.Xr execve 2 ;
the call
.Fn fcntl d F_SETFD 0
restores the default,
which is to not close the descriptor.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn close
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa d
is not an active descriptor.
.It Bq Er EINTR
An interrupt was received.
.It Bq Er EIO
An I/O error occurred while writing to the file system.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr closefrom 2 ,
.Xr dup2 2 ,
.Xr execve 2 ,
.Xr fcntl 2 ,
.Xr flock 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
.Xr socketpair 2
.Sh STANDARDS
.Fn close
conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn close
system call first appeared in
.At v1 .