FATTACH(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
fattach — attach a STREAMS-based file descriptor to a file in the file system name space (STREAMS)

SYNOPSIS

#include <stropts.h>

int fattach(int fildes, const char *path);

DESCRIPTION
The fattach() function shall attach a STREAMS-based file descriptor to a file, effectively associating a pathname with fildes. The application shall ensure that the fildes argument is a valid open file descriptor associated with a STREAMS file. The path argument points to a pathname of an existing file. The application shall have appropriate privileges or be the owner of the file named by path and have write permission. A successful call to fattach() shall cause all pathnames that name the file named by path to name the STREAMS file associated with fildes, until the STREAMS file is detached from the file. A STREAMS file can be attached to more than one file and can have several pathnames associated with it.

The attributes of the named STREAMS file shall be initialized as follows: the permissions, user ID, group ID, and times are set to those of the file named by path, the number of links is set to 1, and the size and device identifier are set to those of the STREAMS file associated with fildes. If any attributes of the named STREAMS file are subsequently changed (for example, by chmod()), neither the attributes of the underlying file nor the attributes of the STREAMS file to which fildes refers shall be affected.

File descriptors referring to the underlying file, opened prior to an fattach() call, shall continue to refer to the underlying file.

RETURN VALUE
Upon successful completion, fattach() shall return 0. Otherwise, -1 shall be returned and errno set to indicate the error.

ERRORS
The fattach() function shall fail if:

EACCES
    Search permission is denied for a component of the path prefix, or the process is the owner of path but does not have write permissions on the file named by path.

EBADF
    The fildes argument is not a valid open file descriptor.

EBUSY
    The file named by path is currently a mount point or has a STREAMS file attached to it.

ELOOP
    A loop exists in symbolic links encountered during resolution of the path argument.

ENAMETOOLONG
    The length of a component of a pathname is longer than {NAME_MAX}.

ENOENT
    A component of path does not name an existing file or path is an empty string.

ENOTDIR
    A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory, or the path argument contains at least one non-<slash> character and ends with one or more trailing <slash> characters.

EPERM
    The effective user ID of the process is not the owner of the file named by path and the process does not have appropriate privileges.

The fattach() function may fail if:

EINVAL
    The fildes argument does not refer to a STREAMS file.

ELOOP
    More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

ENAMETOOLONG
    The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.

EXDEV
    A link to a file on another file system was attempted.

The following sections are informative.

EXAMPLES

  Attaching a File Descriptor to a File

In the following example, fd refers to an open STREAMS file. The call to fattach() associates this STREAM with the file /tmp/named-STREAM, such that any future calls to open /tmp/named-STREAM, prior to breaking the attachment via a call to fdetach(), will instead create a new file handle referring to the STREAMS file associated with fd.

    #include <stropts.h>
    ...
        int fd;
        char *pathname = "/tmp/named-STREAM";
        int ret;

        ret = fattach(fd, pathname);

APPLICATION USAGE
The fattach() function behaves similarly to the traditional mount() function in the way a file is temporarily replaced by the root directory of the mounted file system. In the case of fattach(), the replaced file need not be a directory and the replacing file is a STREAMS file.

RATIONALE
The file attributes of a file which has been the subject of an fattach() call are specifically set because of an artifact of the original implementation. The internal mechanism was the same as for the mount() function. Since mount() is typically only applied to directories, the effects when applied to a regular file are a little surprising, especially as regards the link count which rigidly remains one, even if there were several links originally and despite the fact that all original links refer to the STREAM as long as the fattach() remains in effect.

FUTURE DIRECTIONS
The fattach() function may be removed in a future version.

SEE ALSO
fdetach(), isastream()

The Base Definitions volume of POSIX.1-2017, <stropts.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

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