0000831: How to allocate memory for readdir_r is unclear.

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Category

Severity

Type

Date Submitted

Last Update

0000831

[1003.1(2013)/Issue7+TC1] System Interfaces

Editorial

Clarification Requested

2014-03-29 23:16

2014-04-03 15:35

Reporter

sstewartgallus

View Status

public

Assigned To

Priority

normal

Resolution

Duplicate

Status

Closed

Name

Steven Stewart-Gallus

Organization

User Reference

Section

readdir_r

Page Number

Line Number

Interp Status

---

Final Accepted Text

Summary

0000831: How to allocate memory for readdir_r is unclear.

Description

The Linux man-pages project suggests that one allocates memory for the
entry structure passed to readdir_r as follows:

    len = offsetof(struct dirent, d_name) +
              pathconf(dirpath, _PC_NAME_MAX) + 1
    entryp = malloc(len);

This seems wrong, the Linux man-pages say that _PC_NAME_MAX returns
the maximum length of a filename that a process is allowed to create
and not the maximum length of a filename allowed in a directory.

The POSIX standard does not give a clear explanation of how to
allocate memory for the directory entries. I hypothesize that what is
intended is that one allocates space for an entry with a name
containing at least {NAME_MAX}+1 elements and that one reallocates the
entry length (perhaps doubling or tripling it) when an EOVERFLOW error
occurs.

POSIX seems to suggest this interpretation in it's explanation for
fpathconf, and pathconf:

    Note that implementations are allowed to accept pathnames longer
    than {PATH_MAX} bytes long, but are not allowed to return
    pathnames longer than this unless the user specifies a larger
    buffer using a function that provides a buffer size argument.

This suggest that one would not get an entry from readdir_r if the
entry was too small but only possibly an EOVERFLOW error.

Given that there are misunderstandings of how to use the readdir_r
function out in the wild and that POSIX does not give a clear
explanation I would like to request an example in the standard
clarifying how one should use the readdir_r function.

Desired Action

Please add a clarifying example to the documentation for readdir_r.

Tags

No tags attached.

Attached Files

Relationships

duplicate of

0000696

Closed

either NAME_MAX shouldn't be optional, or readdir_r() needs clarification

Notes
(0002208) eblake (manager) 2014-03-29 23:33	We are proposing marking readdir_r as obsolete in the next version of the standard, because its interface is inherently unusable by design. See more details in 0000696

(0002209) sstewartgallus (reporter) 2014-03-29 23:56 edited on: 2014-03-30 00:17	Thank you, my apologies for opening a duplicate issue. I will eagerly follow the status in http://austingroupbugs.net/view.php?id=696 [^]

Issue History
Date Modified	Username	Field	Change
2014-03-29 23:16	sstewartgallus	New Issue
2014-03-29 23:16	sstewartgallus	Name	=> Steven Stewart-Gallus
2014-03-29 23:16	sstewartgallus	Section	=> readdir_r
2014-03-29 23:32	eblake	Relationship added	duplicate of 0000696
2014-03-29 23:33	eblake	Note Added: 0002208
2014-03-29 23:56	sstewartgallus	Note Added: 0002209
2014-03-30 00:16	sstewartgallus	Note Edited: 0002209
2014-03-30 00:17	sstewartgallus	Note Edited: 0002209
2014-03-30 00:17	sstewartgallus	Note Edited: 0002209
2014-04-03 15:35	nick	Interp Status	=> ---
2014-04-03 15:35	nick	Status	New => Closed
2014-04-03 15:35	nick	Resolution	Open => Duplicate

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