PATH_MAX true POSIX size?

[Heny Townsend]

I notice that PATH_MAX on Solaris is at (2**n - 1):

% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

Whereas on Linux and FreeBSD it's the full round number (256/1024 on
FreeBSD, 256/4096 on Linux). Did somebody read POSIX wrong? Or is it a
case where POSIX is unclear and Sun decided to be pessimistic while the
freebies were optimistic? Or maybe Solaris is counting on the fact that
a request for 1023 bytes will generally be padded to 1024, thus allowing
a "hidden" spot for the null byte and avoiding programmer off-by-one errors?

Notice that it's not just the interpretation of PATH_MAX that differs.
They disagree on the interpretation of _POSIX_PATH_MAX too.

[Heiner Steven]

Post by Heny Townsend
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

I tried this with Solaris 8, and could not verify your results:

$ getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255

Post by Heny Townsend
Whereas on Linux and FreeBSD it's the full round number (256/1024 on
FreeBSD, 256/4096 on Linux). Did somebody read POSIX wrong? Or is it a
case where POSIX is unclear and Sun decided to be pessimistic while the
freebies were optimistic? Or maybe Solaris is counting on the fact that
a request for 1023 bytes will generally be padded to 1024, thus allowing
a "hidden" spot for the null byte and avoiding programmer off-by-one errors?
Notice that it's not just the interpretation of PATH_MAX that differs.
They disagree on the interpretation of _POSIX_PATH_MAX too.

POSIX (at least IEEE Std 1003.1, 2004 Edition) is clear on this:

PATH_MAX
Maximum number of bytes in a pathname, including the terminating
null character. Minimum Acceptable Value: _POSIX_PATH_MAX
[...]

_POSIX_PATH_MAX
Maximum number of bytes in a pathname. Value: 256

So it seems that with Solaris 8 "getconf" prints PATH_MAX correctly,
but prints a wrong result for _POSIX_PATH_MAX .

Confusingly enough NAME_MAX (the length of a path component) does not
include the terminating null character:

NAME_MAX
Maximum number of bytes in a filename (not including terminating
null). Minimum Acceptable Value: _POSIX_NAME_MAX

_POSIX_NAME_MAX
Maximum number of bytes in a filename (not including terminating
null). Value: 14

Solaris 2.8 and (SuSE) Linux both get this right.

Heiner

[Heny Townsend]

Post by Heiner Steven

Post by Heny Townsend
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

$ getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255

Interesting. My results are from Solaris 9 and are quite verifiable:

% uname -a
SunOS xxxxx 5.9 Generic_117171-13 sun4u sparc SUNW,Ultra-5_10
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

But hang on, let me fire up my beta of Solaris 10 from a few months ago ...

% getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255
_XOPEN_PATH_MAX: 1024

Sheesh, they're all over the map on such a basic thing! And they still
don't know that POSIX says _POSIX_PATH_MAX *must* be 256? Someone from
Sun please restore my faith!

[Richard B. Gilbert]

Post by Heny Townsend

Post by Heiner Steven

Post by Heny Townsend
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

$ getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255

% uname -a
SunOS xxxxx 5.9 Generic_117171-13 sun4u sparc SUNW,Ultra-5_10
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255
But hang on, let me fire up my beta of Solaris 10 from a few months ago ...
% getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255
_XOPEN_PATH_MAX: 1024
Sheesh, they're all over the map on such a basic thing! And they still
don't know that POSIX says _POSIX_PATH_MAX *must* be 256? Someone from
Sun please restore my faith!

sunburn_$ uname -a
SunOS sunburn 5.9 Generic sun4u sparc SUNW,Ultra-5_10
sunburn_$ getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255

I upgraded Sunburn from Solaris 8 a few months ago.

sunblok_$ uname -a
SunOS sunblok 5.8 Generic_117350-12 sun4u sparc SUNW,Ultra-5_10
sunblok_$ getconf -a | grep PATH_MAX
_POSIX_PATH_MAX: 255
PATH_MAX: 1024

[Alex Zarutin]

bash-2.05$ uname -a
SunOS qadmz41 5.9 Generic_117171-08 sun4u sparc SUNW,Sun-Fire-V240
bash-2.05$ getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255
bash-2.05$

[Geoff Clare]

Post by Heny Townsend
Sheesh, they're all over the map on such a basic thing! And they still
don't know that POSIX says _POSIX_PATH_MAX *must* be 256?

The cause of the confusion was POSIX itself. Up until the 2001 revision
it was unclear whether PATH_MAX included the null terminator or not,
and _POSIX_PATH_MAX was required to be 255. In the 2001 revision the
confusion was fixed by requiring PATH_MAX to include the null, and
_POSIX_PATH_MAX was changed to 256 to match.

[Joerg Schilling]

Post by Geoff Clare

Post by Heny Townsend
Sheesh, they're all over the map on such a basic thing! And they still
don't know that POSIX says _POSIX_PATH_MAX *must* be 256?

The cause of the confusion was POSIX itself. Up until the 2001 revision
it was unclear whether PATH_MAX included the null terminator or not,
and _POSIX_PATH_MAX was required to be 255. In the 2001 revision the
confusion was fixed by requiring PATH_MAX to include the null, and
_POSIX_PATH_MAX was changed to 256 to match.

Which is even honored by Solaris 10 (the first POSIX.1-2001 Solaris system).
It depenfs on XGP6 to return 256 instead of 255.

[Casper H.S. Dik]

Post by Heny Townsend
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

I get:

/bin/getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255

on everything from Solaris 7 to 10. (may not have checked 8).

What are you running, which shell?

Note that both numbers are correct; PATH_MAX/1024 is the path buffer size and
_POSIX_PATH_MAX is the minimal acceptable value. It is defined in
XPG4 and before as 255; only XPG6 defines it asa 256.

Post by Heny Townsend
Whereas on Linux and FreeBSD it's the full round number (256/1024 on
FreeBSD, 256/4096 on Linux). Did somebody read POSIX wrong? Or is it a
case where POSIX is unclear and Sun decided to be pessimistic while the
freebies were optimistic? Or maybe Solaris is counting on the fact that
a request for 1023 bytes will generally be padded to 1024, thus allowing
a "hidden" spot for the null byte and avoiding programmer off-by-one errors?
Notice that it's not just the interpretation of PATH_MAX that differs.
They disagree on the interpretation of _POSIX_PATH_MAX too.

255 for _POSIX_PATH_MAX is right for all environments except XPG6+.

Where did you get the PATH_MAX = 1023 output from? I can't reproduce
it anywhere.

Casper

[Heny Townsend]

Post by Casper H.S. Dik

Post by Heny Townsend
% getconf -a | grep PATH_MAX
PATH_MAX: 1023
_POSIX_PATH_MAX: 255

/bin/getconf -a | grep PATH_MAX
PATH_MAX: 1024
_POSIX_PATH_MAX: 255
on everything from Solaris 7 to 10. (may not have checked 8).
What are you running, which shell?

I brought up a new shell to verify my previous results and instead got
the same as you. For a few minutes I thought I was going crazy because
the previous 1023 value was cut and pasted on the exact same machine.
But then I figured it out. I have ClearCase installed here. In normal
UFS space getconf returns 1024 while in MVFS space it shows 1023.

So apparently the 255/256 difference is explained by evolution of
standards, while the 1023/1024 difference is something the makers of
ClearCase would be best equipped to explain. Sorry for the FUD.