d639820bc8
better represent failures of special files accessed over NFS. Approved by: schweikh (mentor) Reviewed by: bde (as a description) MFC after: 6 weeks
329 lines
9.1 KiB
Groff
329 lines
9.1 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)open.2 8.2 (Berkeley) 11/16/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd November 16, 1993
|
|
.Dt OPEN 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm open
|
|
.Nd open or create a file for reading or writing
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In fcntl.h
|
|
.Ft int
|
|
.Fn open "const char *path" "int flags" "..."
|
|
.Sh DESCRIPTION
|
|
The file name specified by
|
|
.Fa path
|
|
is opened
|
|
for reading and/or writing as specified by the
|
|
argument
|
|
.Fa flags
|
|
and the file descriptor returned to the calling process.
|
|
The
|
|
.Fa flags
|
|
argument may indicate the file is to be
|
|
created if it does not exist (by specifying the
|
|
.Dv O_CREAT
|
|
flag).
|
|
In this case
|
|
.Fn open
|
|
requires a third argument
|
|
.Fa "mode_t mode" ,
|
|
and the file is created with mode
|
|
.Fa mode
|
|
as described in
|
|
.Xr chmod 2
|
|
and modified by the process' umask value (see
|
|
.Xr umask 2 ) .
|
|
.Pp
|
|
The flags specified are formed by
|
|
.Em or Ns 'ing
|
|
the following values
|
|
.Pp
|
|
.Bd -literal -offset indent -compact
|
|
O_RDONLY open for reading only
|
|
O_WRONLY open for writing only
|
|
O_RDWR open for reading and writing
|
|
O_NONBLOCK do not block on open
|
|
O_APPEND append on each write
|
|
O_CREAT create file if it does not exist
|
|
O_TRUNC truncate size to 0
|
|
O_EXCL error if create and file exists
|
|
O_SHLOCK atomically obtain a shared lock
|
|
O_EXLOCK atomically obtain an exclusive lock
|
|
O_DIRECT eliminate or reduce cache effects
|
|
O_FSYNC synchronous writes
|
|
O_NOFOLLOW do not follow symlinks
|
|
.Ed
|
|
.Pp
|
|
Opening a file with
|
|
.Dv O_APPEND
|
|
set causes each write on the file
|
|
to be appended to the end.
|
|
If
|
|
.Dv O_TRUNC
|
|
is specified and the
|
|
file exists, the file is truncated to zero length.
|
|
If
|
|
.Dv O_EXCL
|
|
is set with
|
|
.Dv O_CREAT
|
|
and the file already
|
|
exists,
|
|
.Fn open
|
|
returns an error.
|
|
This may be used to
|
|
implement a simple exclusive access locking mechanism.
|
|
If
|
|
.Dv O_EXCL
|
|
is set and the last component of the pathname is
|
|
a symbolic link,
|
|
.Fn open
|
|
will fail even if the symbolic
|
|
link points to a non-existent name.
|
|
If the
|
|
.Dv O_NONBLOCK
|
|
flag is specified and the
|
|
.Fn open
|
|
system call would result
|
|
in the process being blocked for some reason (e.g., waiting for
|
|
carrier on a dialup line),
|
|
.Fn open
|
|
returns immediately.
|
|
The descriptor remains in non-blocking mode for subsequent operations.
|
|
.Pp
|
|
If
|
|
.Dv O_FSYNC
|
|
is used in the mask, all writes will
|
|
immediately be written to disk,
|
|
the kernel will not cache written data
|
|
and all writes on the descriptor will not return until
|
|
the data to be written completes.
|
|
.Pp
|
|
If
|
|
.Dv O_NOFOLLOW
|
|
is used in the mask and the target file passed to
|
|
.Fn open
|
|
is a symbolic link then the
|
|
.Fn open
|
|
will fail.
|
|
.Pp
|
|
When opening a file, a lock with
|
|
.Xr flock 2
|
|
semantics can be obtained by setting
|
|
.Dv O_SHLOCK
|
|
for a shared lock, or
|
|
.Dv O_EXLOCK
|
|
for an exclusive lock.
|
|
If creating a file with
|
|
.Dv O_CREAT ,
|
|
the request for the lock will never fail
|
|
(provided that the underlying file system supports locking).
|
|
.Pp
|
|
.Dv O_DIRECT
|
|
may be used to minimize or eliminate the cache effects of reading and writing.
|
|
The system will attempt to avoid caching the data you read or write.
|
|
If it cannot avoid caching the data,
|
|
it will minimize the impact the data has on the cache.
|
|
Use of this flag can drastically reduce performance if not used with care.
|
|
.Pp
|
|
If successful,
|
|
.Fn open
|
|
returns a non-negative integer, termed a file descriptor.
|
|
It returns -1 on failure.
|
|
The file pointer used to mark the current position within the
|
|
file is set to the beginning of the file.
|
|
.Pp
|
|
When a new file is created it is given the group of the directory
|
|
which contains it.
|
|
.Pp
|
|
The new descriptor is set to remain open across
|
|
.Xr execve 2
|
|
system calls; see
|
|
.Xr close 2
|
|
and
|
|
.Xr fcntl 2 .
|
|
.Pp
|
|
The system imposes a limit on the number of file descriptors
|
|
open simultaneously by one process.
|
|
The
|
|
.Xr getdtablesize 2
|
|
system call returns the current system limit.
|
|
.Sh RETURN VALUES
|
|
If successful,
|
|
.Fn open
|
|
returns a non-negative integer, termed a file descriptor.
|
|
It returns -1 on failure, and sets
|
|
.Va errno
|
|
to indicate the error.
|
|
.Sh ERRORS
|
|
The named file is opened unless:
|
|
.Bl -tag -width Er
|
|
.It Bq Er ENOTDIR
|
|
A component of the path prefix is not a directory.
|
|
.It Bq Er ENAMETOOLONG
|
|
A component of a pathname exceeded 255 characters,
|
|
or an entire path name exceeded 1023 characters.
|
|
.It Bq Er ENOENT
|
|
.Dv O_CREAT
|
|
is not set and the named file does not exist.
|
|
.It Bq Er ENOENT
|
|
A component of the path name that must exist does not exist.
|
|
.It Bq Er EACCES
|
|
Search permission is denied for a component of the path prefix.
|
|
.It Bq Er EACCES
|
|
The required permissions (for reading and/or writing)
|
|
are denied for the given flags.
|
|
.It Bq Er EACCES
|
|
.Dv O_CREAT
|
|
is specified,
|
|
the file does not exist,
|
|
and the directory in which it is to be created
|
|
does not permit writing.
|
|
.It Bq Er ELOOP
|
|
Too many symbolic links were encountered in translating the pathname.
|
|
.It Bq Er EISDIR
|
|
The named file is a directory, and the arguments specify
|
|
it is to be opened for writing.
|
|
.It Bq Er EROFS
|
|
The named file resides on a read-only file system,
|
|
and the file is to be modified.
|
|
.It Bq Er EMFILE
|
|
The process has already reached its limit for open file descriptors.
|
|
.It Bq Er ENFILE
|
|
The system file table is full.
|
|
.It Bq Er EMLINK
|
|
.Dv O_NOFOLLOW
|
|
was specified and the target is a symbolic link.
|
|
.It Bq Er ENXIO
|
|
The named file is a character special or block
|
|
special file, and the device associated with this special file
|
|
does not exist.
|
|
.It Bq Er ENXIO
|
|
The named file is a fifo, no process has
|
|
it open for reading, and the arguments specify it is
|
|
to be opened for writing.
|
|
.It Bq Er EINTR
|
|
The
|
|
.Fn open
|
|
operation was interrupted by a signal.
|
|
.It Bq Er EOPNOTSUPP
|
|
.Dv O_SHLOCK
|
|
or
|
|
.Dv O_EXLOCK
|
|
is specified but the underlying file system does not support locking.
|
|
.It Bq Er EOPNOTSUPP
|
|
The named file is a special file mounted through a filesystem that
|
|
does not support access to it (e.g. NFS).
|
|
.It Bq Er EWOULDBLOCK
|
|
.Dv O_NONBLOCK
|
|
and one of
|
|
.Dv O_SHLOCK
|
|
or
|
|
.Dv O_EXLOCK
|
|
is specified and the file is locked.
|
|
.It Bq Er ENOSPC
|
|
.Dv O_CREAT
|
|
is specified,
|
|
the file does not exist,
|
|
and the directory in which the entry for the new file is being placed
|
|
cannot be extended because there is no space left on the file
|
|
system containing the directory.
|
|
.It Bq Er ENOSPC
|
|
.Dv O_CREAT
|
|
is specified,
|
|
the file does not exist,
|
|
and there are no free inodes on the file system on which the
|
|
file is being created.
|
|
.It Bq Er EDQUOT
|
|
.Dv O_CREAT
|
|
is specified,
|
|
the file does not exist,
|
|
and the directory in which the entry for the new file
|
|
is being placed cannot be extended because the
|
|
user's quota of disk blocks on the file system
|
|
containing the directory has been exhausted.
|
|
.It Bq Er EDQUOT
|
|
.Dv O_CREAT
|
|
is specified,
|
|
the file does not exist,
|
|
and the user's quota of inodes on the file system on
|
|
which the file is being created has been exhausted.
|
|
.It Bq Er EIO
|
|
An I/O error occurred while making the directory entry or
|
|
allocating the inode for
|
|
.Dv O_CREAT .
|
|
.It Bq Er ETXTBSY
|
|
The file is a pure procedure (shared text) file that is being
|
|
executed and the
|
|
.Fn open
|
|
system call requests write access.
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa path
|
|
argument
|
|
points outside the process's allocated address space.
|
|
.It Bq Er EEXIST
|
|
.Dv O_CREAT
|
|
and
|
|
.Dv O_EXCL
|
|
were specified and the file exists.
|
|
.It Bq Er EOPNOTSUPP
|
|
An attempt was made to open a socket (not currently implemented).
|
|
.It Bq Er EINVAL
|
|
An attempt was made to open a descriptor with an illegal combination
|
|
of
|
|
.Dv O_RDONLY ,
|
|
.Dv O_WRONLY ,
|
|
and
|
|
.Dv O_RDWR .
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr chmod 2 ,
|
|
.Xr close 2 ,
|
|
.Xr dup 2 ,
|
|
.Xr getdtablesize 2 ,
|
|
.Xr lseek 2 ,
|
|
.Xr read 2 ,
|
|
.Xr umask 2 ,
|
|
.Xr write 2 ,
|
|
.Xr fopen 3
|
|
.Sh HISTORY
|
|
The
|
|
.Fn open
|
|
function appeared in
|
|
.At v6 .
|