WG15 Defect Report Ref: 9945-1-30
Topic: Max # of directory levels

This is an approved interpretation of 9945-1:1990.


Last update: 1997-05-20

                                                                9945-1-90 #30

	Topic:			Max # of directory levels
	Relevant Sections:	2.3.6
	Classification:		No Change required.

Defect Report:

I wish for an interpretation of ISO/IEC 9945-1 (ISO/IEC 9945-1) regarding
the maximum number of directory levels that a conforming implementation must
support. The value {PATH_MAX} defines the maximum number of bytes in a pathname.
The error [ENAMETOOLONG] is returned when the length of the path or file 
arguments exceeds {PATH_MAX}. All other references to {PATH_MAX} are to
arguments or the result of the pathconf() function.

All the arguments that are checked against {PATH_MAX} go thru pathname
resolution (2.3.6). However, the current working directory mechanism can be used
to effectively by-pass any limits imposed by {PATH_MAX}. If the pathname is too
long, change the current working directory to some directory on the pathname,
delete upto and including that directory, and try again. {PATH_MAX} only
controls how many directories can be described at any one call.

If this is the correct interpretation, it would prevent a conforming 
implementation on file systems that associates each file with an absolute 
pathname (with filename) stored in a limited size array. Such a file system
is used on A Series from Unisys, and I suspect on many other operating systems.
I hope that instead the correct interpretation is that the maximum number of
directory levels that a conforming implementation must support is limited by
{PATH_MAX} when expressed as an absolute pathname. Note that this would not
restrict what an implementation may support, only what it must support.

WG15 response for 9945-1:1990 (9945-1:1990):

No, {PATH_MAX} was not intended to constrain actual absolute pathnames.

{PATH_MAX} specifies the length of the string that can be
passed to any of a number of POSIX.1 interfaces as an
argument that represents a pathname.  ISO/IEC 9945-1:1990
does not state an upper limit or a lower limit for the
number of levels in directory hierarchies that must be

Since {PATH_MAX} is not the maximum length of an absolute path,
the absolute path for a file can be much longer than {PATH_MAX}
as long as the pathname used to refer to the file is not longer
than {PATH_MAX}.

Rationale for Interpretation: