elladan@eskimo.com (Elladan) wrote on 16.07.02 in <20020717022252.GA30570@eskimo.com>:
> I believe this demonstrates the need for a standard, one way, or the
> other. :-)
So then let's see what the actual standard says ...
--- snip ---
The Open Group Base Specifications Issue 6
IEEE Std 1003.1-2001
Copyright + 2001 The IEEE and The Open Group, All Rights reserved.
_________________________________________________________________
NAME
close - close a file descriptor
SYNOPSIS
#include <unistd.h>
int close(int fildes);
DESCRIPTION
The close() function shall deallocate the file descriptor indicated
by fildes. To deallocate means to make the file descriptor
available for return by subsequent calls to open() or other
functions that allocate file descriptors. All outstanding record
locks owned by the process on the file associated with the file
descriptor shall be removed (that is, unlocked).
If close() is interrupted by a signal that is to be caught, it
shall return -1 with errno set to [EINTR] and the state of fildes
is unspecified. If an I/O error occurred while reading from or
writing to the file system during close(), it may return -1 with
errno set to [EIO]; if this error is returned, the state of fildes
is unspecified.
When all file descriptors associated with a pipe or FIFO special
file are closed, any data remaining in the pipe or FIFO shall be
discarded.
When all file descriptors associated with an open file description
have been closed, the open file description shall be freed.
If the link count of the file is 0, when all file descriptors
associated with the file are closed, the space occupied by the file
shall be freed and the file shall no longer be accessible.
[XSR] [Option Start] If a STREAMS-based fildes is closed and the
calling process was previously registered to receive a SIGPOLL
signal for events associated with that STREAM, the calling process
shall be unregistered for events associated with the STREAM. The
last close() for a STREAM shall cause the STREAM associated with
fildes to be dismantled. If O_NONBLOCK is not set and there have
been no signals posted for the STREAM, and if there is data on the
module's write queue, close() shall wait for an unspecified time
(for each module and driver) for any output to drain before
dismantling the STREAM. The time delay can be changed via an
I_SETCLTIME ioctl() request. If the O_NONBLOCK flag is set, or if
there are any pending signals, close() shall not wait for output to
drain, and shall dismantle the STREAM immediately.
If the implementation supports STREAMS-based pipes, and fildes is
associated with one end of a pipe, the last close() shall cause a
hangup to occur on the other end of the pipe. In addition, if the
other end of the pipe has been named by fattach(), then the last
close() shall force the named end to be detached by fdetach(). If
the named end has no open file descriptors associated with it and
gets detached, the STREAM associated with that end shall also be
dismantled. [Option End]
[XSI] [Option Start] If fildes refers to the master side of a
pseudo-terminal, and this is the last close, a SIGHUP signal shall
be sent to the process group, if any, for which the slave side of
the pseudo-terminal is the controlling terminal. It is unspecified
whether closing the master side of the pseudo-terminal flushes all
queued input and output. [Option End]
[XSR] [Option Start] If fildes refers to the slave side of a
STREAMS-based pseudo-terminal, a zero-length message may be sent to
the master. [Option End]
[AIO] [Option Start] When there is an outstanding cancelable
asynchronous I/O operation against fildes when close() is called,
that I/O operation may be canceled. An I/O operation that is not
canceled completes as if the close() operation had not yet
occurred. All operations that are not canceled shall complete as if
the close() blocked until the operations completed. The close()
operation itself need not block awaiting such I/O completion.
Whether any I/O operation is canceled, and which I/O operation may
be canceled upon close(), is implementation-defined. [Option End]
[MF|SHM] [Option Start] If a shared memory object or a memory
mapped file remains referenced at the last close (that is, a
process has it mapped), then the entire contents of the memory
object shall persist until the memory object becomes unreferenced.
If this is the last close of a shared memory object or a memory
mapped file and the close results in the memory object becoming
unreferenced, and the memory object has been unlinked, then the
memory object shall be removed. [Option End]
If fildes refers to a socket, close() shall cause the socket to be
destroyed. If the socket is in connection-mode, and the SO_LINGER
option is set for the socket with non-zero linger time, and the
socket has untransmitted data, then close() shall block for up to
the current linger interval until all data is transmitted.
RETURN VALUE
Upon successful completion, 0 shall be returned; otherwise, -1
shall be returned and errno set to indicate the error.
ERRORS
The close() function shall fail if:
[EBADF]
The fildes argument is not a valid file descriptor.
[EINTR]
The close() function was interrupted by a signal.
The close() function may fail if:
[EIO]
An I/O error occurred while reading from or writing to the file
system.
_________________________________________________________________
The following sections are informative.
EXAMPLES
Reassigning a File Descriptor
The following example closes the file descriptor associated with
standard output for the current process, re-assigns standard output
to a new file descriptor, and closes the original file descriptor
to clean up. This example assumes that the file descriptor 0 (which
is the descriptor for standard input) is not closed.
#include <unistd.h>
...
int pfd;
...
close(1);
dup(pfd);
close(pfd);
...
Incidentally, this is exactly what could be achieved using:
dup2(pfd, 1);
close(pfd);
Closing a File Descriptor
In the following example, close() is used to close a file
descriptor after an unsuccessful attempt is made to associate that
file descriptor with a stream.
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#define LOCKFILE "/etc/ptmp"
...
int pfd;
FILE *fpfd;
...
if ((fpfd = fdopen (pfd, "w")) == NULL) {
close(pfd);
unlink(LOCKFILE);
exit(1);
}
...
APPLICATION USAGE
An application that had used the stdio routine fopen() to open a
file should use the corresponding fclose() routine rather than
close(). Once a file is closed, the file descriptor no longer
exists, since the integer corresponding to it no longer refers to a
file.
RATIONALE
The use of interruptible device close routines should be
discouraged to avoid problems with the implicit closes of file
descriptors by exec and exit(). This volume of IEEE Std 1003.1-2001
only intends to permit such behavior by specifying the [EINTR]
error condition.
FUTURE DIRECTIONS
None.
SEE ALSO
STREAMS , fattach() , fclose() , fdetach() , fopen() , ioctl() ,
open() , the Base Definitions volume of IEEE Std 1003.1-2001,
<unistd.h>
CHANGE HISTORY
First released in Issue 1. Derived from Issue 1 of the SVID.
Issue 5
The DESCRIPTION is updated for alignment with the POSIX Realtime
Extension.
Issue 6
The DESCRIPTION related to a STREAMS-based file or pseudo-terminal
is marked as part of the XSI STREAMS Option Group.
The following new requirements on POSIX implementations derive from
alignment with the Single UNIX Specification:
* The [EIO] error condition is added as an optional error.
* The DESCRIPTION is updated to describe the state of the fildes
file descriptor as unspecified if an I/O error occurs and an [EIO]
error condition is returned.
Text referring to sockets is added to the DESCRIPTION.
The DESCRIPTION is updated for alignment with IEEE Std 1003.1j-2000
by specifying that shared memory objects and memory mapped files
(and not typed memory objects) are the types of memory objects to
which the paragraph on last closes applies.
End of informative text.
_________________________________________________________________
_________________________________________________________________
UNIX « is a registered Trademark of The Open Group.
POSIX « is a registered Trademark of The IEEE.
[ Main Index | XBD | XCU | XSH | XRAT ]
_________________________________________________________________
--- snip ---
The standard is very explicit here: When close() returns an error,
*YOU LOSE*.
MfG Kai
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Tue Jul 23 2002 - 22:00:23 EST