FATTACH(3P)

💅 FATTACH(3P) 💅

okay so bestie, buckle up, because we're reading fattach from the POSIX Programmer's Manual (that's the 3P in the corner, iykyk) and honestly? it's giving niche-but-iconic. STREAMS content, no cap.

✨ PROLOG ✨

Real talk before we even start: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, go read the corresponding Linux manual page for the deets on Linux behavior), or the interface may not be implemented on Linux at all. 💀 Yes, that's a real possibility. We move.

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🌸 NAME 🌸

fattach — attach a STREAMS-based file descriptor to a file in the file system name space (STREAMS). It's exactly what it says on the tin, periodt.

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🦋 SYNOPSIS 🦋

#include <stropts.h>

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

two arguments, one vibe. let's go.

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💖 DESCRIPTION 💖

The fattach() function shall attach a STREAMS-based file descriptor to a file, effectively associating a pathname with fildes. that's the whole point of her existence.

Here's the tea on who's responsible for what:

• You, the application, shall ensure that the fildes argument is a valid open file descriptor associated with a STREAMS file. that's on you bestie, not on fattach().
• 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. pick a lane, either works.

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. and no, she's not monogamous — a STREAMS file can be attached to more than one file and can have several pathnames associated with it. polyamorous file descriptor energy, we love to see it. 👑

The attributes of the named STREAMS file shall be initialized as follows — literally just copy these down, this is the important part:

• 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
• the size and device identifier are set to those of the STREAMS file associated with fildes

and 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. so no messy cross-contamination, okay? they're independent. mind your business. 🙈

One more thing, and it matters: file descriptors referring to the underlying file, opened prior to an fattach() call, shall continue to refer to the underlying file. they don't get rewired, they don't get an invite to the new party. they're grandfathered in.

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⭐ RETURN VALUE ⭐

• Upon successful completion, fattach() shall return 0. 🎉 slay.
• Otherwise, -1 shall be returned and errno set to indicate the error. 😭 not slay.

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🔥 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. you own it but you can't write to it? tragic. heartbreaking, even.
• EBADF — The fildes argument is not a valid open file descriptor. bestie that's not a file descriptor, that's a vibe.
• EBUSY — The file named by path is currently a mount point or has a STREAMS file attached to it. she's taken, back off.
• ELOOP — A loop exists in symbolic links encountered during resolution of the path argument. it's giving circular. we're going in circles. literally.
• 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. nothing there. void. ghost town.
• 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. not your file, not your privileges, not your moment. 🚫

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. cross-filesystem linking? not today, not ever.

The following sections are informative. (translation: the ✨lore✨ is over, now we're just gossiping.)

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🎀 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. iconic behavior tbh.

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

    ret = fattach(fd, pathname);

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🧚 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. but here's the plot twist: in the case of fattach(), the replaced file need not be a directory and the replacing file is a STREAMS file. so it's like mount() but with main character energy and fewer rules. 💅

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👑 RATIONALE 👑

ngl this part is juicy. 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. so yeah. the link count is stubborn. it simply will not budge. that's just how it is, no notes. 😌

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🌈 FUTURE DIRECTIONS 🌈

The fattach() function may be removed in a future version. enjoy her while she's here bestie, she's on borrowed time. 💀

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🫶 SEE ALSO 🫶

• fdetach()
• isastream()
• The Base Definitions volume of POSIX.1‐2017, <stropts.h>

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💜 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie! this one came to you courtesy of IEEE/The Open Group, 2017, FATTACH(3P). go forth and attach responsibly. mwah. 💖✨🎀