133 lines
3.9 KiB
Groff
133 lines
3.9 KiB
Groff
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.\" $NetBSD: close.2,v 1.17 2004/06/01 16:14:10 kleink Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)close.2 8.2 (Berkeley) 4/19/94
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.\"
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.Dd April 19, 1994
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.Dt CLOSE 2
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.Os
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.Sh NAME
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.Nm close
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.Nd delete a descriptor
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn close "int d"
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.Sh DESCRIPTION
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The
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.Fn close
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system call deletes a descriptor from the per-process object
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reference table.
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If this is the last reference to the underlying object, the
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object will be deactivated.
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For example, on the last close of a file the current
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.Em seek
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pointer associated with the file is lost; on the last close of a
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.Xr socket 2
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associated naming information and queued data are discarded; on
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the last close of a file holding an advisory lock the lock is
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released (see
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.Xr flock 2 ) .
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.Pp
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When a process exits, all associated descriptors are freed, but
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since there is a limit on active descriptors per processes, the
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.Fn close
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system call
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is useful when a large quantity of file descriptors are being handled.
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.Pp
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When a process calls
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.Xr fork 2 ,
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all descriptors for the new child process reference the same
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objects as they did in the parent before the
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.Fn fork .
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If a new process is then to be run using
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.Xr execve 2 ,
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the process would normally inherit these descriptors.
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Most of the descriptors can be rearranged with
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.Xr dup2 2
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or deleted with
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.Fn close
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before the
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.Fn execve
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is attempted, but if some of these descriptors will still be needed if the
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.Fn execve
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fails, it is necessary to arrange for them to be closed only if the
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.Fn execve
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succeeds.
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For this reason, the system call
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.Bl -item -offset indent
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.It
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.Fn fcntl d F_SETFD 1 ;
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.El
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.Pp
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is provided,
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which arranges that a descriptor
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.Dq Fa d
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will be closed after a successful
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.Fn execve ;
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the system call
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.Bl -item -offset indent
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.It
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.Fn fcntl d F_SETFD 0 ;
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.El
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.Pp
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restores the default, which is to not close descriptor
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.Dq Fa d .
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.Sh RETURN VALUES
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Upon successful completion, a value of 0 is returned.
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Otherwise, a value of \-1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn close
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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.Fa d
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is not an active descriptor.
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.It Bq Er EINTR
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An interrupt was received.
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.El
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr execve 2 ,
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.Xr fcntl 2 ,
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.Xr flock 2 ,
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.Xr open 2 ,
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.Xr pipe 2 ,
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.Xr socket 2 ,
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.Xr socketpair 2
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.Sh STANDARDS
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The
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.Fn close
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function conforms to
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.St -p1003.1-90 .
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