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c4f16b69e1
any open file descriptors >= 'lowfd'. It is largely identical to the same function on other operating systems such as Solaris, DFly, NetBSD, and OpenBSD. One difference from other *BSD is that this closefrom() does not fail with any errors. In practice, while the manpages for NetBSD and OpenBSD claim that they return EINTR, they ignore internal errors from close() and never return EINTR. DFly does return EINTR, but for the common use case (closing fd's prior to execve()), the caller really wants all fd's closed and returning EINTR just forces callers to call closefrom() in a loop until it stops failing. Note that this implementation of closefrom(2) does not make any effort to resolve userland races with open(2) in other threads. As such, it is not multithread safe. Submitted by: rwatson (initial version) Reviewed by: rwatson MFC after: 2 weeks
141 lines
4.2 KiB
Groff
141 lines
4.2 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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.\" 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 December 4, 2006
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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
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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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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 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.
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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, FD_CLOEXEC)
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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 RETURN VALUES
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.Rv -std close
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.Sh ERRORS
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The
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.Fn close
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system call will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa d
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argument
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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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.It Bq Er ENOSPC
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The underlying object did not fit, cached data was lost.
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.It Bq Er ECONNRESET
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The underlying object was a stream socket that was shut down by the peer
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before all pending data was delivered.
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.El
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr closefrom 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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system call is expected to conform to
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.St -p1003.1-90 .
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.Sh HISTORY
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The
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.Fn close
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function appeared in
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.At v7 .
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