2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
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11 KiB
Groff
377 lines
11 KiB
Groff
.\" $NetBSD: open.2,v 1.47 2010/09/22 17:58:09 wiz Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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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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.\" @(#)open.2 8.2 (Berkeley) 11/16/93
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.\"
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.Dd September 22, 2010
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.Dt OPEN 2
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.Os
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.Sh NAME
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.Nm open
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.Nd open or create a file for reading or writing
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In fcntl.h
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.Ft int
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.Fn open "const char *path" "int flags" "mode_t mode"
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.Sh DESCRIPTION
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The file name specified by
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.Fa path
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is opened
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for reading and/or writing as specified by the
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argument
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.Fa flags
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and the file descriptor returned to the calling process.
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The
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.Fa flags
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are specified by
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.Em or Ns 'ing
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the values listed below.
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Applications must specify exactly one of the first three values
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(file access methods):
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.Bl -tag -offset indent -width O_NONBLOCK
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.It Dv O_RDONLY
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Open for reading only.
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.It Dv O_WRONLY
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Open for writing only.
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.It Dv O_RDWR
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Open for reading and writing.
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.El
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.Pp
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Any combination of the following may be used:
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.Bl -tag -offset indent -width O_NONBLOCK
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.It Dv O_NONBLOCK
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Do not block on open or for data to become available.
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.It Dv O_APPEND
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Append to the file on each write.
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.It Dv O_CREAT
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Create the file if it does not exist, in which case the file is
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created with mode
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.Ar mode
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as described in
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.Xr chmod 2
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and modified by the process' umask value (see
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.Xr umask 2 ) .
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.It Dv O_TRUNC
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Truncate size to 0.
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.It Dv O_EXCL
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Error if
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.Dv O_CREAT
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and the file already exists.
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.It Dv O_SHLOCK
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Atomically obtain a shared lock.
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.It Dv O_EXLOCK
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Atomically obtain an exclusive lock.
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.It Dv O_NOFOLLOW
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If last path element is a symlink, don't follow it.
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This option is provided for compatibility with other operating
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systems, but its security value is questionable.
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.It Dv O_DSYNC
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If set, write operations will be performed according to synchronized
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I/O data integrity completion:
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each write will wait for the file data to be committed to stable
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storage.
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.It Dv O_SYNC
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If set, write operations will be performed according to synchronized
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I/O file integrity completion:
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each write will wait for both the file data and file status to be
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committed to stable storage.
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.It Dv O_RSYNC
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If set, read operations will complete at the same level of
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integrity which is in effect for write operations:
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if specified together with
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.Dv O_SYNC ,
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each read will wait for the file status to be committed to stable
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storage.
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.Pp
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Combining
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.Dv O_RSYNC
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with
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.Dv O_DSYNC
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only, or specifying it without any other synchronized I/O integrity
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completion flag set, has no further effect.
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.It Dv O_ALT_IO
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Alternate I/O semantics will be used for read and write operations
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on the file descriptor.
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Alternate semantics are defined by the underlying layers and will not
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have any alternate effect in most cases.
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.It Dv O_NOCTTY
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If the file is a terminal device, the opened device is not
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made the controlling terminal for the session.
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This flag has no effect on
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.Nx ,
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since the system defaults to the abovementioned behaviour.
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The flag is present only for standards conformance.
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.It Dv O_DIRECT
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If set on a regular file, data I/O operations will not buffer the data
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being transferred in the kernel's cache, but rather transfer the data
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directly between user memory and the underlying device driver if possible.
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This flag is advisory; the request may be performed in the normal
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buffered fashion if certain conditions are not met, e.g. if the request
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is not sufficiently aligned or if the file is mapped.
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.Pp
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To meet the alignment requirements for direct I/O, the file offset,
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the length of the I/O and the address of the buffer in memory must all
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be multiples of
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.Dv DEV_BSIZE
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(512 bytes).
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If the I/O request is made
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using an interface that supports scatter/gather via struct iovec, each
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element of the request must meet the above alignment constraints.
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.It Dv O_DIRECTORY
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Fail if the file is not a directory.
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.El
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.Pp
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Opening a file with
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.Dv O_APPEND
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set causes each write on the file
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to be appended to the end.
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If
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.Dv O_TRUNC
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is specified and the
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file exists, the file is truncated to zero length.
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.Pp
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If
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.Dv O_EXCL
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is set with
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.Dv O_CREAT
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and the file already
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exists,
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.Fn open
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returns an error.
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This may be used to implement a simple exclusive access locking mechanism.
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If
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.Dv O_EXCL
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is set and the last component of the pathname is
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a symbolic link,
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.Fn open
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will fail even if the symbolic
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link points to a non-existent name.
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.Pp
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If the
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.Dv O_NONBLOCK
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flag is specified, do not wait for the device or file to be ready or
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available.
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If the
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.Fn open
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call would result
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in the process being blocked for some reason (e.g., waiting for
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carrier on a dialup line),
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.Fn open
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returns immediately.
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This flag also has the effect of making all subsequent I/O on the open file non-blocking.
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.Pp
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When opening a file, a lock with
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.Xr flock 2
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semantics can be obtained by setting
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.Dv O_SHLOCK
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for a shared lock, or
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.Dv O_EXLOCK
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for an exclusive lock.
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If creating a file with
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.Dv O_CREAT ,
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the request for the lock will never fail
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(provided that the underlying filesystem supports locking).
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.Pp
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If
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.Fn open
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is successful, the file pointer used to mark the current position within
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the file is set to the beginning of the file.
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.Pp
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When a new file is created it is given the group of the directory
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which contains it.
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.Pp
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The new descriptor is set to remain open across
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.Xr execve 2
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system calls; see
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.Xr close 2
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and
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.Xr fcntl 2 .
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.Pp
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The system imposes a limit on the number of file descriptors
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open simultaneously by one process.
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Calling
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.Xr getdtablesize 3
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returns the current system limit.
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.Sh RETURN VALUES
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If successful,
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.Fn open
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returns a non-negative integer, termed a file descriptor.
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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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The named file is opened unless:
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.Bl -tag -width Er
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix,
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the required permissions (for reading and/or writing)
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are denied for the given flags, or
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the directory in which it is to be created
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does not permit writing.
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.It Bq Er EDQUOT
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the directory in which the entry for the new file
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is being placed cannot be extended because the
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user's quota of disk blocks on the file system
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containing the directory has been exhausted; or
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the user's quota of inodes on the file system on
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which the file is being created has been exhausted.
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.It Bq Er EEXIST
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.Dv O_CREAT
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and
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.Dv O_EXCL
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were specified and the file exists.
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.It Bq Er EFAULT
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.Fa path
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points outside the process's allocated address space.
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.It Bq Er EFTYPE
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.Dv O_NOFOLLOW
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was specified, but the last path component is a symlink.
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.Em Note :
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.St -p1003.1-2008
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specifies returning
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.Bq Er ELOOP
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for this case.
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.It Bq Er EINTR
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The
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.Fn open
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operation was interrupted by a signal.
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.It Bq Er EIO
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An I/O error occurred while making the directory entry or
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allocating the inode for
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.Dv O_CREAT .
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.It Bq Er EISDIR
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The named file is a directory, and the arguments specify
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it is to be opened for writing.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EMFILE
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The process has already reached its limit for open file descriptors.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Brq Dv NAME_MAX
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characters, or an entire path name exceeded
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.Brq Dv PATH_MAX
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characters.
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.It Bq Er ENFILE
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The system file table is full.
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.It Bq Er ENOENT
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.Dv O_CREAT
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is not set and the named file does not exist, or
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a component of the path name that must exist does not exist.
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.It Bq Er ENOSPC
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the directory in which the entry for the new file is being placed
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cannot be extended because there is no space left on the file
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system containing the directory; or
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and there are no free inodes on the file system on which the
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file is being created.
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory; or
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.Dv O_DIRECTORY
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is specified and the last path component is not a directory.
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.It Bq Er ENXIO
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The named file is a character special or block
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special file, and the device associated with this special file
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does not exist, or
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the named file is a
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.Tn FIFO ,
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.Dv O_NONBLOCK
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and
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.Dv O_WRONLY
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is set and no process has the file open for reading.
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.It Bq Er EOPNOTSUPP
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.Dv O_SHLOCK
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or
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.Dv O_EXLOCK
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is specified but the underlying filesystem does not support locking; or
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an attempt was made to open a socket (not currently implemented).
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.It Bq Er EPERM
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The file's flags (see
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.Xr chflags 2 )
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don't allow the file to be opened.
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.It Bq Er EROFS
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The named file resides on a read-only file system,
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and the file is to be modified.
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.It Bq Er ETXTBSY
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The file is a pure procedure (shared text) file that is being
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executed and the
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.Fn open
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call requests write access.
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.El
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.Sh SEE ALSO
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.Xr chmod 2 ,
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.Xr close 2 ,
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.Xr dup 2 ,
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.Xr lseek 2 ,
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.Xr read 2 ,
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.Xr umask 2 ,
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.Xr write 2 ,
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.Xr getdtablesize 3
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.Sh STANDARDS
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The
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.Fn open
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function conforms to
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.St -p1003.1-90 .
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The
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.Fa flags
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values
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.Dv O_DSYNC ,
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.Dv O_SYNC
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and
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.Dv O_RSYNC
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are extensions defined in
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.St -p1003.1b-93 .
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.Pp
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The
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.Dv O_SHLOCK
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and
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.Dv O_EXLOCK
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flags are non-standard extensions and should not be used if portability
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is of concern.
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.Sh HISTORY
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An
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.Fn open
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function call appeared in
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.At v2 .
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