156 lines
4.5 KiB
Groff
156 lines
4.5 KiB
Groff
.\" 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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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.\" $FreeBSD$
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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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.Fd #include <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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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
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the current
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.Em seek
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pointer associated with the file is lost;
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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;
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on the last close of a file holding an advisory lock
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the lock is released (see further
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.Xr flock 2 ) .
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However, the semantics of System V and
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.St -p1003.1-88
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dictate that all
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.Xr fcntl 2
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advisory record locks associated with a file for a given process
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are removed when
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.Em any
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file descriptor for that file is closed by that process.
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.Pp
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When a process exits,
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all associated file descriptors are freed, but since there is
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a limit on active descriptors per processes, the
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.Fn close
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function 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 forks (see
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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 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. Most
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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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.Xr execve 2
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is attempted, but if some of these descriptors will still
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be needed if the execve fails, it is necessary to arrange for them
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to be closed if the execve succeeds.
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For this reason, the call
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.Dq Li fcntl(d, F_SETFD, 1)
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is provided,
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which arranges that a descriptor will be closed after a successful
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execve; the call
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.Dq Li fcntl(d, F_SETFD, 0)
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restores the default,
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which is to not close the descriptor.
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.Sh IMPLEMENTATION NOTES
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In the non-threaded library
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.Fn close
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is implemented as the
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.Va close
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syscall.
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.Pp
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In the threaded library, the
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.Va close
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syscall is assembled to
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.Fn _thread_sys_close
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and
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.Fn close
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is implemented as a function which locks
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.Fa d
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for read and write, then calls
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.Fn _thread_sys_close .
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Before returning,
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.Fn close
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unlocks
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.Fa d .
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.Sh RETURN VALUES
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.Rv -std close
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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 call is expected to conform to
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.St -p1003.1-90 .
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.Sh HISTORY
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A
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.Fn close
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function call appeared in
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.At v7 .
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